Search results for: stress strain relation

Authors: Djamal Hamadi, Sifeddine Abderrahmani, Toufik Maalem, Oussama Temami

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In recent years many finite elements have been developed for plate bending analysis. The formulated elements are based on the strain based approach. This approach leads to the representation of the displacements by higher order polynomial terms without the need for the introduction of additional internal and unnecessary degrees of freedom. Good convergence can also be obtained when the results are compared with those obtained from the corresponding displacement based elements, having the same total number of degrees of freedom. Furthermore, the plate bending elements are free from any shear locking since they converge to the Kirchhoff solution for thin plates contrarily for the corresponding displacement based elements. In this paper the efficiency of the strain based approach compared to well known displacement formulation is presented. The results obtained by a new formulated plate bending element based on the strain approach and Kirchhoff theory are compared with some others elements. The good convergence of the new formulated element is confirmed.

Keywords: displacement fields, finite elements, plate bending, Kirchhoff theory, strain based approach

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Authors: V. K. Gupta, Tejeet Singh

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In many whisker reinforced composites, anisotropy may result due to material flow during processing operations such as forging, extrusion etc. The consequence of anisotropy, introduced during processing of disc material, has been investigated on the steady state creep deformations of the rotating disc. The disc material is assumed to undergo plastic deformations according to Hill’s anisotropic criterion. Steady state creep has been analyzed in a constant thickness rotating disc made of functionally graded 6061Al-SiCw (where the subscript ‘w’ stands for whisker) using Hill’s The content of reinforcement (SiCw) in the disc is assumed to decrease linearly from the inner to outer radius. The stresses and strain rates in the disc are estimated by solving the force equilibrium equation along with the constitutive equations describing multi-axial creep. The results obtained for anisotropic FGM disc have been compared with those estimated for isotropic FGM disc having the same average whisker content. The anisotropic constants, appearing in Hill’s yield criterion, have been obtained from the available experimental results. The results show that the presence of anisotropy reduces the tangential stress in the middle of the disc but near the inner and outer radii the tangential stress is higher when compared to isotropic disc. On the other hand, the steady state creep rates in the anisotropic disc are reduced significantly over the entire disc radius, with the maximum reduction observed at the inner radius. Further, in the presence of anisotropy the distribution of strain rate becomes relatively uniform over the entire disc, which may be responsible for reducing the extent of distortion in the disc.

Keywords: anisotropy, creep, functionally graded composite, rotating disc

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Authors: Ram Mohan, Mahendran Samykano, Shyam Aravamudhan

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Metallic nanowires with sub-micron and hundreds of nanometer diameter have a diversity of applications in nano/micro-electromechanical systems (NEMS/MEMS). Characterizing the mechanical properties of such sub-micron and nano-scale metallic nanowires are tedious; require sophisticated and careful experimentation to be performed within high-powered microscopy systems (scanning electron microscope (SEM), atomic force microscope (AFM)). Also, needed are nanoscale devices for placing the nanowires; loading them with the intended conditions; obtaining the data for load–deflection during the deformation within the high-powered microscopy environment poses significant challenges. Even picking the grown nanowires and placing them correctly within a nanoscale loading device is not an easy task. Mechanical characterizations through experimental methods for such nanowires are still very limited. Various techniques at different levels of fidelity, resolution, and induced errors have been attempted by material science and nanomaterial researchers. The methods for determining the load, deflection within the nanoscale devices also pose a significant problem. The state of the art is thus still at its infancy. All these factors result and is seen in the wide differences in the characterization curves and the reported properties in the current literature. In this paper, we discuss and present our experimental method, results, and discussions of uniaxial tensile loading and the development of subsequent stress–strain characteristics curves for Nickel nanowires. Nickel nanowires in the diameter range of 220–270 nm were obtained in our laboratory via an electrodeposition method, which is a solution based, template method followed in our present work for growing 1-D Nickel nanowires. Process variables such as the presence of magnetic field, its intensity; and varying electrical current density during the electrodeposition process were found to influence the morphological and physical characteristics including crystal orientation, size of the grown nanowires1. To further understand the correlation and influence of electrodeposition process variables, associated formed structural features of our grown Nickel nanowires to their mechanical properties, careful experiments within scanning electron microscope (SEM) were conducted. Details of the uniaxial tensile characterization, testing methodology, nanoscale testing device, load–deflection characteristics, microscopy images of failure progression, and the subsequent stress–strain curves are discussed and presented.

Keywords: uniaxial tensile characterization, nanowires, electrodeposition, stress-strain, nickel

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Authors: Eshwara Prasad Koorapati, R. Raman Goud, Swadesh Kumar Singh

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In the present work forming limit diagrams and strain distribution profile diagrams for extra deep drawing steel at room and elevated temperatures have been determined experimentally by conducting stretch forming experiments by using designed and fabricated warm stretch forming tooling setup. With the help of forming Limit Diagrams (FLDs) and strain distribution profile diagrams the formability of Extra Deep Drawing steel has been analyzed and co-related with mechanical properties like strain hardening coefficient (n) and normal anisotropy (r−).Mechanical properties of EDD steel from room temperature to 4500 C were determined and discussed the impact of temperature on the properties like work hardening exponent (n) anisotropy (r-) and strength coefficient of the material. Also, the fractured surfaces after stretching have undergone the some metallurgical investigations and attempt has been made to co-relate with the formability of EDD steel sheets. They are co-related and good agreement with FLDs at various temperatures.

Keywords: FLD, micro hardness, strain distribution profile, stretch forming

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Authors: Junior Nomani

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This paper presents a novel approach to modelling the metal cutting of duplex stainless steels, a two-phase alloy regarded as a difficult-to-machine material. Calculation and control of shear strain and stresses during cutting are essential to achievement of ideal cutting conditions. Too low or too high leads to higher required cutting force or excessive heat generation causing premature tool wear failure. A 2D finite element cutting model was created based on electron backscatter diffraction (EBSD) data imagery of duplex microstructure. A mesh was generated using ‘object-oriented’ software OOF2 version V2.1.11, converting microstructural images to quadrilateral elements. A virtual workpiece was created on ABAQUS modelling software where a rigid body toolpiece advanced towards workpiece simulating chip formation, generating serrated edge chip formation cutting. Model results found calculated stress strain contour plots correlated well with similar finite element models tied with austenite stainless steel alloys. Virtual chip form profile is also similar compared experimental frozen machining chip samples. The output model data provides new insight description of strain behavior of two phase material on how it transitions from workpiece into the chip.

Keywords: Duplex stainless steel, ABAQUS, OOF2, Chip formation

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Authors: Parveen K. Saini, Tarun Agarwal

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An investigation into the effect of countersunk depth, plate thickness, countersunk angle and plate width on the stress concentration around countersunk hole is carried out with the help of finite element analysis. The variation of stress concentration with respect to these parameters is studied for three types of loading viz. uniformly distributed load, uniformly varying load and functionally distributed load. The results of the finite element analysis are interpreted and some conclusions are drawn. The distribution of stress concentration around countersunk hole in isotropic plates simply supported at all the edges is found similar and is independent of loading. The maximum stress concentration also occurs at a particular point irrespective of the loading conditions.

Keywords: stress concentration factor, countersunk hole, finite element, ANSYS

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Authors: Naeim Akbari Shahkhosravi, Reza Kakavand, Helen M. S. Davies, Amin Komeili

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Equine locomotion and performance are significantly affected by hoof health. One of the most critical diseases of the hoof is laminitis, which can lead to horse lameness in a severe condition. This disease exhibits the mechanical properties degradation of the laminar junction tissue within the hoof. Therefore, it is essential to investigate the biomechanics of the hoof, focusing specifically on excessive and cumulatively accumulated stresses within the laminar junction tissue. For this aim, the current study generated a novel equine hoof Finite Element (FE) model under dynamic physiological loading conditions and employing a hyperelastic material model. Associated tissues of the equine hoof were segmented from computed tomography scans of an equine forelimb, including the navicular bone, third phalanx, sole, frog, laminar junction, digital cushion, and medial- dorsal- lateral wall areas. The inner tissues were connected based on the hoof anatomy, and the hoof was under a dynamic loading over cyclic strides at the trot. The strain distribution on the hoof wall of the model was compared with the published in vivo strain measurements to validate the model. Then the validated model was used to study the development of laminitis. The ultimate stress tolerated by the laminar junction before rupture was considered as a stress threshold. The tissue damage was simulated through iterative reduction of the tissue’s mechanical properties in the presence of excessive maximum principal stresses. The findings of this investigation revealed how damage initiates from the medial and lateral sides of the tissue and propagates through the hoof dorsal area.

Keywords: horse hoof, laminitis, finite element model, continuous damage

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Authors: Alexander Pesin, Denis Pustovoytov, Mikhail Sverdlik

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Materials with ultrafine-grained structure and unique physical and mechanical properties can be obtained by methods of severe plastic deformation, which include processes of asymmetric rolling (AR). Asymmetric rolling is a very effective way to create ultrafine-grained structures of metals and alloys. Since the asymmetric rolling is a continuous process, it has great potential for industrial production of ultrafine-grained structure sheets. Basic principles of asymmetric rolling are described in detail in scientific literature. In this work finite element modeling of asymmetric rolling and metal forming processes in multiroll gauge was performed. Parameters of the processes which allow achieving significant values of shear strain were defined. The results of the study will be useful for the research of the evolution of ultra-fine metal structure in asymmetric rolling.

Keywords: asymmetric rolling, equivalent strain, FEM, multiroll gauge, profile, severe plastic deformation, shear strain, sheet

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Authors: Mohammad Vahedi Torshizi

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In this investigation, at first, bending stress, contact stress, Safety factor of bending and Safety factor of contact between sun gear and planet gear tooth was determined using mathematical equations. Also, The amount of Sun Revolution in, Speed carrier, power Transmitted of the sun, sun torque, sun peripheral speed, Enter the tangential force gears, was calculated using mathematical equations. According to the obtained results, maximum of bending stress and contact stress occurred in three plantary and low status of four plantary. Also, maximum of Speed carrier, sun peripheral speed, Safety factor of bending and Safety factor of contact obtained in four plantary and maximum of power Transmitted of the sun, Enter the tangential force gears, bending stress and contact stress was in three pantry and factors And other factors were equal in the two planets.

Keywords: bending stress, contact stress, plantary, mathematical equations

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Authors: Onwumere O. J.

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The teaching of stress at any level of education could be a daunting task for the second language teacher because most times, they are bereft of the right approach to use in teaching it even at the fact is that, teaching it. But the fact is that teaching stress even at the middle basic could be interesting if the right approach is employed. To this end, the researcher was of the view that grouping could be a very good strategy to employ in order to sustain the interest of the learner and that the use at drums would be a good way to concretise the teaching of stress at this level. He was able to do this by discussing stress, grouping as a good technique, and the use of drums in teaching stress. To establish the fact that the use of drums would be very effective, four research questions contained in a questionnaire were structured. Three hundred (300) teachers of English in four tertiary institutions, three secondary schools and three primary schools in Nigeria were used. Based on the data analysis and findings, suggestions were given on how teachers and learners could use drums to make the teaching and learning of stress enjoyable for both teachers and learners at the middle basic of education.

Keywords: concretise, grouping, right approach, second language

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Authors: Won Mog Choi, Seong Kyeong Hong, Seok Young Jeong

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The stress on the buried pipeline under pavement is significantly affected by vehicle loads and elastic modulus of the soil surrounding the pipeline. The correct elastic modulus of soil has to be applied to the finite element model to investigate the effect of the vehicle loads on the buried pipeline using finite element analysis. The purpose of this study is to establish the approach to calculating the correct elastic modulus of soil using the optimization process. The optimal elastic modulus of soil, which minimizes the difference between the strain measured from vehicle driving test at the velocity of 35km/h and the strain calculated from finite element analyses, was calculated through the optimization process using multi-response surface methodology. Three elastic moduli of soil (road layer, original soil, dense sand) surrounding the pipeline were defined as the variables for the optimization. Further analyses with the optimal elastic modulus at the velocities of 4.27km/h, 15.47km/h, 24.18km/h were performed and compared to the test results to verify the applicability of multi-response surface methodology. The results indicated that the strain of the buried pipeline was mostly affected by the elastic modulus of original soil, followed by the dense sand and the load layer, as well as the results of further analyses with optimal elastic modulus of soil show good agreement with the test.

Keywords: pipeline, optimization, elastic modulus of soil, response surface methodology

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Authors: Rafik Baouche, Rabah Chaouchi

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This work reports the first comprehensive stress field interpretation from the eleven recently drilled wells in the Berkaoui Basin, Algerian Sahara. A cumulative length of 7000+m acoustic image logs from 06 vertical wells were investigated, and a mean NW-SE (128°-145° N) maximum horizontal stress (SHMax) orientation is inferred from the B-D quality wellbore breakouts. The study integrates log-based approach with the downhole measurements to infer pore pressure, in-situ stress magnitudes. Vertical stress (Sv), interpreted from the bulk-density profiles, has an average gradient of 22.36 MPa/km. The Ordovician and Cambrian reservoirs have a pore pressure gradient of 13.47-13.77 MPa/km, which is more than the hydrostatic pressure regime. A 17.2-18.3 MPa/km gradient of minimum horizontal stress (Shmin) is inferred from the fracture closure pressure in the reservoirs. Breakout widths constrained the SHMax magnitude in the 23.8-26.5 MPa/km range. Subsurface stress distribution in the central Saharan Algeria indicates that the present-day stress field in the Berkaoui Basin is principally strike-slip faulting (SHMax > Sv > Shmin). Inferences are drawn on the regional stress pattern and drilling and reservoir development.

Keywords: stress, imagery, breakouts, sahara

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Authors: Thomas P. Roper, Brad Forbes, Jurij Karlovšek

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Shear displacement along bedding defects is a well-recognised behaviour when tunnelling and mining in stratified rock. This deformation can affect the durability and integrity of installed rock bolts. In-situ monitoring of rock bolt deformation under bedding shear cannot be accurately derived from traditional strain gauge bolts as sensors are too large and spaced too far apart to accurately assess concentrated displacement along discrete defects. A possible solution to this is the use of fiber optic technologies developed for precision monitoring. Distributed Optic Sensor (DOS) embedded rock bolts were installed in a tunnel project with the aim of measuring the bolt deformation profile under significant shear displacements. This technology successfully measured the 3D strain distribution along the bolts when subjected to bedding shear and resolved the axial and lateral strain constituents in order to determine the deformational geometry of the bolts. The results are compared well with the current visual method for monitoring shear displacement using borescope holes, considering this method as suitable.

Keywords: distributed optical strain sensing, rock bolt, bedding shear, sandstone tunnel

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Authors: Aneesh Joshi, Sagil James

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Cold Spray (CS) process is deposition of solid particles over a substrate above a certain critical impact velocity. Unlike thermal spray processes, CS process does not melt the particles thus retaining their original physical and chemical properties. These characteristics make CS process ideal for various engineering applications involving metals, polymers, ceramics and composites. The bonding mechanism involved in CS process is extremely complex considering the dynamic nature of the process. Though CS process offers great promise for several engineering applications, the realization of its full potential is limited by the lack of understanding of the complex mechanisms involved in this process and the effect of critical process parameters on the deposition efficiency. The goal of this research is to understand the complex nanoscale mechanisms involved in CS process. The study uses Molecular Dynamics (MD) simulation technique to understand the material deposition phenomenon during the CS process. Impact of a single crystalline copper nanoparticle on copper substrate is modelled under varying process conditions. The quantitative results of the impacts at different velocities, impact angle and size of the particles are evaluated using flattening ratio, von Mises stress distribution and local shear strain. The study finds that the flattening ratio and hence the quality of deposition was highest for an impact velocity of 700 m/s, particle size of 20 Å and an impact angle of 90°. The stress and strain analysis revealed regions of shear instabilities in the periphery of impact and also revealed plastic deformation of the particles after the impact. The results of this study can be used to augment our existing knowledge in the field of CS processes.

Keywords: cold spray process, molecular dynamics simulation, nanoparticles, particle impact

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Authors: Mohamed Boualem Salah

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The size and shape of soil particles reflect the formation history of the grains. In turn, the macro scale behavior of the soil mass results from particle level interactions which are affected by particle shape. Sphericity, roundness and smoothness characterize different scales associated to particle shape. New experimental data and data from previously published studies are gathered into two databases to explore the effects of particle shape on packing as well as small and large-strain properties of sandy soils. Data analysis shows that increased particle irregularity (angularity and/or eccentricity) leads to: an increase in emax and emin, a decrease in stiffness yet with increased sensitivity to the state of stress, an increase in compressibility under zero-lateral strain loading, and an increase in critical state friction angle φcs and intercept Γ with a weak effect on slope λ. Therefore, particle shape emerges as a significant soil index property that needs to be properly characterized and documented, particularly in clean sands and gravels. The systematic assessment of particle shape will lead to a better understanding of sand behavior.

Keywords: angularity, eccentricity, shape particle, behavior of soil

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Authors: Priyakant Vaghela, Jagdish Prajapati

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Bending stress at the root of the gear tooth is the very important criteria in gear design and it should be kept the minimum. Minimization of bending stress at the root of the gear tooth is a recent demand from industry. This paper presents an innovative approach to obtain minimum bending stress at the root of a tooth by optimizing tooth root profile and drive side pressure angle. Circular-filleted at the root of the tooth is widely used in the design. Circular fillet creates discontinuity at the root of the tooth. So, at root stress concentration occurs. In order to minimize stress concentration, an important criterion is a G2 continuity at the blending of the gear tooth. A Bezier curve is used with G2 continuity at the root of asymmetric spur gear tooth. The comparison has been done between normal and modified tooth using ANSYS simulation. Tooth root profile and drive side pressure angle are optimized to minimize bending stress at the root of the tooth of the asymmetric involute spur gear. Von Mises stress of optimized profile is analyzed and compared with normal profile symmetric gear. Von Mises stress is reducing by 31.27% by optimization of drive side pressure angle and root profile. Stress concentration of modified gear was significantly reduced.

Keywords: asymmetric spur gear tooth, G2 continuity, pressure angle, stress concentration at the root of tooth, tooth root stress

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Authors: F. Husem, M. E. Turan, Y. Sun, H. Ahlatci, I. Tozlu

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Residual stress and fatigue crack growth rates are important to determine mechanical behavior of rails. This study aims to make relationship between residual stress and fatigue crack growth values in rails. For this purpose, three R260 quality rails (0.6-0.8% C, 0.6-1.25 Mn) were chosen. Residual stress of samples was measured by cutting method that is related in railway standard. Then samples were machined for fatigue crack growth test and analyze was completed according to the ASTM E647 standard which gives information about parameters of rails for this test. Microstructure characterizations were examined by Light Optic Microscope (LOM). The results showed that residual stress change with fatigue crack growth rate. The sample has highest residual stress exhibits highest crack growth rate and pearlitic structure can be seen clearly for all samples by microstructure analyze.

Keywords: residual stress, fatigue crack growth, R260, SEM, ASTM E647

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Authors: Amin Derakhshan, Mohammad Mikaili, Mohammad Ali Khalilzadeh, Amin Mohammadian

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This paper proposes a stress recognition system from multi-modal bio-potential signals. For stress recognition, Support Vector Machines (SVM) and LDA are applied to design the stress classifiers and its characteristics are investigated. Using gathered data under psychological polygraph experiments, the classifiers are trained and tested. The pattern recognition method classifies stressful from non-stressful subjects based on labels which come from polygraph data. The successful classification rate is 96% for 12 subjects. It means that facial thermal imaging due to its non-contact advantage could be a remarkable alternative for psycho-physiological methods.

Keywords: stress, thermal imaging, face, SVM, polygraph

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Authors: Faycal Boughalleb, Raoudha Abdellaoui

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The effect of NaCl stress on root and leaf anatomy was investigated in three Astragalus species grown in 0-300 mM NaCl for 30 days under greenhouse conditions. Root cross section and cortex thickness was reduced under salt stress in both species while A. tenuifolius showed thinner cortex and the root cross section was unchanged. The epidermis stele thickness was unaffected by salinity in A. armatus and A. tenuifolius and was reduced in A. mareoticus with smaller xylem vessel size. In addition, vessel density and wall thickness of xylem was increased under salt conditions in the studies species. The entire lamina and mesophyll of the three species were thinner in salt-stressed plants. A. armatus and A. tenuifolius showed the higher thickness with increased size of the lower epidermis. NaCl (300 mM) reduced leaf water content by 41.5 % in A. mareoticus while it was unchanged in the other species. The size of the vascular bundle increased under salinity in A. tenuifolius leaves and it was unchanged in the other ones. A longer distance between leaf vascular bundle was occurred in A. mareoticus. The effects of NaCl on root and leaf ultrastructure are discussed in relation to the degree of salt resistance of these species. The unchanged biomass production under salt stress confirmed the higher tolerance oft A. tenuifolius to salinity. A. armatus was moderately salt tolerant with decrease of biomass production by 14.2 % while A. mareoticus was considered as salt sensitive plant when the decrease in biomass production reached 56.8%.

Keywords: Astragalus species, leaf ultrastructure, root anatomy, salt stress

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Authors: Rekha S., S. J. Nalini, S. Bhuvana, S. Kanmani, Vidhya Venugopal

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Introduction: Pregnant women's occupational heat exposure has been linked to foetal abnormalities and pregnancy complications. The presence of heat in the workplace is expected to lead to Adverse Pregnancy Outcomes (APO), especially in tropical countries where temperatures are rising and workplace cooling interventions are minimal. For effective interventions, in-depth understanding and evidence about occupational heat stress and APO are required. Methodology: Approximately 800 pregnant women in and around Chennai who were employed in jobs requiring moderate to hard labour participated in the cohort research. During the study period (2014-2019), environmental heat exposures were measured using a Questemp WBGT monitor, and heat strain markers, such as Core Body Temperature (CBT) and Urine Specific Gravity (USG), were evaluated using an Infrared Thermometer and a refractometer, respectively. Using a valid HOTHAPS questionnaire, self-reported health symptoms were collected. In addition, a postpartum follow-up with the mothers was done to collect APO-related data. Major findings of the study: Approximately 47.3% of pregnant workers have workplace WBGTs over the safe manual work threshold value for moderate/heavy employment (Average WBGT of 26.6°C±1.0°C). About 12.5% of the workers had CBT levels above the usual range, and 24.8% had USG levels above 1.020, both of which suggested mild dehydration. Miscarriages (3%), stillbirths/preterm births (3.5%), and low birth weights (8.8%) were the most common unfavorable outcomes among pregnant employees. In addition, WBGT exposures above TLVs during all trimesters were associated with a 2.3-fold increased risk of adverse fetal/maternal outcomes (95% CI: 1.4-3.8), after adjusting for potential confounding variables including age, education, socioeconomic status, abortion history, stillbirth, preterm, LBW, and BMI. The study determined that WBGTs in the workplace had direct short- and long-term effects on the health of both the mother and the foetus. Despite the study's limited scope, the findings provided valuable insights and highlighted the need for future comprehensive cohort studies and extensive data in order to establish effective policies to protect vulnerable pregnant women from the dangers of heat stress and to promote reproductive health.

Keywords: adverse outcome, heat stress, interventions, physiological strain, pregnant women

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Authors: Jeonghun Lee

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Thyroid-stimulating hormone (TSH) is regulated by the negative feedback of T3 and T4 but is affected by cortisol and cytokines during allostasis. Hence, TSH levels can be influenced by stress through cortisol. In the present study, changes in TSH levels under stress and the potential of TSH as a stress marker were examined in patients lacking T3 or T4 feedback after thyroid surgery. The three stress questionnaires (Korean version of the Daily Stress Inventory, Social Readjustment Rating Scale, and Stress Overload Scale-Short [SOSS]), open-ended question (OQ), and thyroid function tests were performed twice in 106 patients enrolled from January 2019 to October 2020. Statistical analysis was performed using the generalized linear mixed effect model (GLMM) in R software version 4.1.0. In a multiple LMM involving 106 patients, T3, T4, SOSS (category), open-ended questions, the extent of thyroidectomy, and preoperative TSH were significantly correlated with lnTSH. T3 and T4 increased by 1 and lnTSH decreased by 0.03, 3.52, respectively. In case of a stressful event on OQ, lnTSH increased by 1.55. In the high-risk group, lnTSH increased by 0.79, compared with the low group (p<0.05). TSH had a significant relationship with stress, together with T3, T4, and the extent of thyroidectomy. As such, it has the potential to be used as a stress marker, though it showed a low correlation with other stress questionnaires. To address this limitation, questionnaires on various social environments and research on copy strategies are necessary for future studies.

Keywords: stress, surgery, thyroid stimulating hormone, thyroidectomy

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Authors: Kwak, Hyo-Gyung, Gang, Han Gul

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In the context of an increasing need for reliability and safety in concrete structures under blast and impact loading condition, the behavior of concrete under high strain rate condition has been an important issue. Since concrete subjected to impact loading associated with high strain rate shows quite different material behavior from that in the static state, several material models are proposed and used to describe the high strain rate behavior under blast and impact loading. In the process of modelling, in advance, mesh dependency in the used finite element (FE) is the key problem because simulation results under high strain-rate condition are quite sensitive to applied FE mesh size. It means that the accuracy of simulation results may deeply be dependent on FE mesh size in simulations. This paper introduces an improved criterion which can minimize the mesh-dependency of simulation results on the basis of the fracture energy concept, and HJC (Holmquist Johnson Cook), CSC (Continuous Surface Cap) and K&C (Karagozian & Case) models are examined to trace their relative sensitivity to the used FE mesh size. To coincide with the purpose of the penetration test with a concrete plate under a projectile (bullet), the residual velocities of projectile after penetration are compared. The correlation studies between analytical results and the parametric studies associated with them show that the variation of residual velocity with the used FE mesh size is quite reduced by applying a unique failure strain value determined according to the proposed criterion.

Keywords: high strain rate concrete, penetration simulation, failure strain, mesh-dependency, fracture energy

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Authors: Anurag Niranjan, Michael Fitzpatrick, Yin Jin Janin, Jazeel Chukkan, Niall Smyth

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Fillet welds are used in joining longitudinal stiffeners in ship structures. Welding residual stresses in fillet welds are generally distributed in a non-uniform manner, as shown in previous research the residual stress redistribution occurs under the cyclic loading that is experienced by such joints during service, and the combination of the initial residual stress, local constraints, and loading can alter the stress field in ways that are extremely difficult to predict. As the residual stress influences the crack propagation originating from the toe of the fillet welds, full understanding of the residual stress field and how it evolves is very important for structural integrity calculations. Knowledge of the residual stress redistribution in the presence of a flaw is therefore required for better fatigue life prediction. Moreover, defect assessment procedures such as BS7910 offer very limited guidance for flaw acceptance and the associated residual stress redistribution in the assessment of fillet welds. Therefore the objective of this work is to study a surface-breaking flaw at the weld toe region in a fillet weld under cyclic load, in conjunction with residual stress measurement at pre-defined crack depths. This work will provide details of residual stress redistribution under cyclic load in the presence of a crack. The outcome of this project will inform integrity assessment with respect to the treatment of residual stress in fillet welds. Knowledge of the residual stress evolution for this weld geometry will be greatly beneficial for flaw tolerance assessments (BS 7910, API 591).

Keywords: fillet weld, fatigue, residual stress, structure integrity

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Authors: Terri A. Croteau, Todd G. Morrison

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Despite increased scholarly attention paid to minority stress and sexual satisfaction among sexual minorities, to the authors’ knowledge, no researchers, to date, have attempted to synthesize this literature. To address this omission, the authors conducted a meta-analytic review of the association between sexual minority stress (i.e., sexual identity stigma, internalized sexual identity stigma, and sexual identity concealment) and sexual satisfaction. Twenty-seven articles containing 58 effect sizes were analyzed (N = 183,582). Findings indicated a small, inverse relationship between these constructs, indicating that minority stress may lead to diminished sexual satisfaction among gay/lesbian and bisexual individuals. Further, the overall effect size varied as a function of minority stress type, such that the effect for internalized stigma was significantly larger than the effects for stigma or concealment. Age also moderated the relationship between minority stress and sexual satisfaction; specifically, older age was associated with a smaller effect, suggesting that older adults may be better at coping with minority stress than younger adults. Limitations, implications, and directions for future research are discussed.

Keywords: minority stress, stigma, sexual satisfaction, sexual minorities

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Authors: Khodamorad Nabaki, Jianhu Shen, Xiaodong Huang

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This paper develops a method for considering the critical fatigue stress as a constraint in the Bi-directional Evolutionary Structural Optimization (BESO) method. Our aim is to reach an optimal design in which high cycle fatigue failure does not occur for a specific life time. The critical fatigue stress is calculated based on modified Goodman criteria and used as a stress constraint in our topology optimization problem. Since fatigue generally does not occur for compressive stresses, we use the p-norm approach of the stress measurement that considers the highest tensile principal stress in each point as stress measure to calculate the sensitivity numbers. The BESO method has been extended to minimize volume an object subjected to the critical fatigue stress constraint. The optimization results are compared with the results from the compliance minimization problem which shows clearly the merits of our newly developed approach.

Keywords: topology optimization, BESO method, p-norm, fatigue constraint

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Authors: Yee-Seul So, Guiseppe Ianiri, Alex Idnurm, Yong-Sun Bahn

Abstract:

Tor1 is a serine/threonine protein kinase that is widely conserved across eukaryotic species. Tor1 was first identified in Saccharomyces cerevisiae as a target of rapamycin (TOR). The TOR pathway has been implicated in regulating cellular responses to nutrients, proliferation, translation, transcription, autophagy, and ribosome biogenesis. Here we identified two homologues of S. cerevisiae Tor proteins, CNAG_06642 (Tor1) and CNAG_05220 (Tlk1, TOR-like kinase 1), in Cryptococcus neoformans causing a life-threatening fungal meningoencephalitis. Both Tor1 and Tlk1 have rapamycin-binding (RB) domains but Tlk1 has truncated RB form. To study the TOR-signaling pathway in the fungal pathogen, we attempt to construct the tor1Δ and tlk1Δ mutants and phenotypically analyze them. Although we failed to construct the tor1Δ mutant, we successfully construct the tlk1Δ mutant. The tlk1Δ mutant does not exhibit any discernable phenotypes, suggesting that Tlk1 is dispensable in C. neoformans. The essentiality of TOR1 is independently confirmed by constructing the TOR1 promoter replacement strain by using a copper transporter 4 (CTR4) promoter and the TOR1/tor1 heterozygous mutant in diploid C. neoformans strain background followed by sporulation analysis. To further analyze the function of Tor1, we construct TOR1 overexpression mutant using a constitutively active histone H3 in C. neoformans. We find that the Tor1 overexpression mutant is resistant to rapamycin but the tlk1Δ mutant does not exhibit any altered resistance to rapamycin, further confirming that Tor1, but not Tlk1, is critical for TOR signaling. Furthermore, we found that Tor1 is involved in response to diverse stresses, including genotoxic stress, oxidative stress, thermo-stress, antifungal drug treatment, and production of melanin. To identify any TOR-related transcription factors, we screened C. neoformans transcription factor library that we constructed in our previous study and identified several potential downstream factors of Tor1, including Atf1, Crg1 and Bzp3. In conclusion, the current study provides insight into the role of the TOR signaling pathway in human fungal pathogens as well as C. neoformans.

Keywords: fungal pathogen, serine/threonine kinase, target of rapamycin, transcription factor

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Authors: Jeries J. Abou-Hanna

Abstract:

Several techniques exist for determining stress-intensity factors in linear elastic fracture mechanics analysis. These techniques are based on analytical, numerical, and empirical approaches that have been well documented in literature and engineering handbooks. However, not all techniques share the same merit. In addition to overly-conservative results, the numerical methods that require extensive computational effort, and those requiring copious user parameters hinder practicing engineers from efficiently evaluating stress-intensity factors. This paper investigates the prospects of reducing the complexity and required variables to determine stress-intensity factors through the utilization of the stress gradient and a weighting function. The heart of this work resides in the understanding that fracture emanating from stress concentration locations cannot be explained by a single maximum stress value approach, but requires use of a critical volume in which the crack exists. In order to understand the effectiveness of this technique, this study investigated components of different notch geometry and varying levels of stress gradients. Two forms of weighting functions were employed to determine stress-intensity factors and results were compared to analytical exact methods. The results indicated that the “exponential” weighting function was superior to the “absolute” weighting function. An error band +/- 10% was met for cases ranging from a steep stress gradient in a sharp v-notch to the less severe stress transitions of a large circular notch. The incorporation of the proposed method has shown to be a worthwhile consideration.

Keywords: fracture mechanics, finite element method, stress intensity factor, stress gradient

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Authors: A. Goodarzian, A. Ghasemipanah, R. Ziaie Moayed, H. Niroumand

Abstract:

The problem of soil stabilization has been one of the important issues in geotechnical engineering. Nowadays, nanomaterials have revolutionized many industries. In this research, improvement of the Kerman fine-grained soil by nanozeolite and nanobentonite additives separately has been investigated using Atterberg Limits and unconfined compression test. In unconfined compression test, the samples were prepared with 3, 5 and 7% nano additives, with 1, 7 and 28 days curing time with strain control method. Finally, the effect of different percentages of nanozeolite and nanobentonite on the geotechnical behavior and characteristics of Kerman fine-grained soil was investigated. The results showed that with increasing the amount of nanozeolite and also nanobentonite to fine-grained soil, the soil exhibits more compression strength. So that by adding 7% nanozeolite and nanobentonite with 1 day curing, the unconfined compression strength is 1.18 and 2.1 times higher than the unstabilized soil. In addition, the failure strain decreases in samples containing nanozeolite, whereas it increases in the presence of nanobentonite. Increasing the percentage of nanozeolite and nanobentonite also increased the elasticity modulus of soil.

Keywords: nanoparticles, soil improvement, clayey soil, unconfined compression stress

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Authors: Aisha Bano, Rizwan Nazir

Abstract:

The present study aimed at exploring the impact of meaning in life on psychological well-being and stress among university students. Victor Frankl's paradigm provided the theoretical foundation for this study. A sample of 560 university students was drawn from Quaid-i-Azam University Islamabad. The sample was drawn using stratified random sampling technique. Data were collected using Existence Scale, Warwick-Edinburg Mental Well-Being Scale, and Stress Scale. Results of linear regression analysis reveals that high perception of meaning in life will lead to high psychological well-being and low stress among university students. Non-significant differences are found on meaning in life variable with regard to gender in the sample using t-test. Together these results suggest that meaning in life independent of gender, is a significant predictor of the levels of stress and psychological well-being being directly related to psychological well-being and inversely related to stress levels.

Keywords: existential meaning in life, psychological well-being, stress, students

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Authors: Petnamnueng Dettipponpong, Shuen E. Chen

Abstract:

Heat stress is known to have negative effects on reproductive functions, such as follicular development and ovulation. This study aimed to investigate the specific effects of heat stress on steroid hormone secretion of ovarian follicle cells, particularly in relation to the expression of Apolipoprotein B (ApoB) and microsomal triglyceride transfer protein (MTP). The aim of the study was to understand the impact of heat stress on steroid hormone secretion in ovarian follicle cells and to explore the role of ApoB and MTP in this process. Primary granulosa and theca cells were collected from follicles and cultured under heat stress conditions (42 °C) for various time periods. Controls were maintained under normal conditions (37.5 °C ). The culture medium was collected at different time points to measure levels of progesterone and estradiol using ELISA kits. ApoB and MTP expression levels were analyzed using homemade antibodies and western blot. Data were assessed by a one-way ANOVA comparison test with Duncan’s new multiple-range test. Results were expressed as mean±S.E. Difference was considered significant at P<0.05. The results showed that heat stress significantly increased progesterone secretion in granulosa cells, with the peak observed after 13 hours of recovery under thermoneutral conditions. Estradiol secretion by theca cells was not affected. Heat stress also had a significant negative effect on granulosa cell viability. Additionally, the expression of ApoB and MTP was found to be differentially regulated by heat stress. ApoB expression in theca cells was transiently promoted, while ApoB expression in granulosa cells was consistently suppressed. MTP expression increased after 5 hours of recovery in both cell types. These findings suggest a mechanism by which chicken follicle cells export cellular lipids as very low-density lipoprotein (VLDL) in response to thermal stress. These contribute to our understanding of the role of ApoB and MTP steroidogenesis and lipid metabolism under heat stress conditions. The study involved the collection of primary granulosa and theca cells, culture under different temperature conditions, and analysis of the culture medium for hormone levels using ELISA kits. ApoB and MTP expression levels were assessed using homemade antibodies and western blot. This study aimed to address the effects of heat stress on steroid hormone secretion in ovarian follicle cells, as well as the role of ApoB and MTP in this process. The study demonstrates that heat stress stimulates steroidogenesis in granulosa cells, affecting progesterone secretion. ApoB and MTP expression were found to be differentially regulated by heat stress, indicating a potential mechanism for the export of cellular lipids in response to thermal stress.

Keywords: heat stress, granulosa cells, theca cells, steroidogenesis, chicken, apolipoprotein B, microsomal triglyceride transfer protein

Procedia PDF Downloads 47