Search results for: strength tests

Authors: Milad Abolfazli, Milad Bazli

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In this critical review, the topic of how composites maintain their tensile strength when exposed to elevated temperatures will be studied. A comprehensive database of 761 tests have been analyzed and closely examined to study the various factors that affect the strength retention. Conclusions are drawn from the collective research efforts of numerous scholars who have investigated this subject. Through the analysis of these tests, the relationships between the tensile strength retention and various effective factors are investigated. This review is meant to be a practical resource for researchers and engineers. It provides valuable information that can guide the development of composites tailored for high-temperature applications. By offering a deeper understanding of how composites behave in extreme heat, the paper contributes to the advancement of materials science and engineering.

Keywords: tesnile tests, high temperatures, FRP composites, mechanical perfomance

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Authors: Feng Fu, Maria Karli

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In this paper, experimental studies were carried out to investigate the behaviour of recycled aggregate concrete (RAC). A number of compressive tests, tensile splitting tests, as well as impact tests were conducted. In the tests, different recycled aggregate replacement ratio, different mix design and different water to cement ratio have been chosen in the investigation. The behavior of the RAC concrete was investigated in detail. The results of the tests show that the water-cement ratio plays an important role in the strength of the concrete and RAC concrete exhibit sufficient strength in comparison to the normal aggregate concrete; the relevant design recommendations are also made.

Keywords: recycled aggregate concrete, compressive test, tensile splitting test, flexural strength test, impact test

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Authors: Jian Zheng, Li Li, Maxime Daviault

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In several cases, one needs apply lubrication materials in laboratory tests to reduce the friction (shear strength) along the interfaces between a tested soil and the side walls of container. Several types of lubricants are available. Their effectiveness had been tested mostly through direct shear tests. These testing conditions are quite different than those when the tested soil is placed in the container. Thus, the shear strengths measured from direct shear tests may not be totally representative of those of interfaces between the tested soil and the sidewalls of container. In this paper, the effectiveness of different lubricants used to reduce the friction (shear strength) of soil-structure interfaces has been studied. Results show that the selected lubricants do not significantly reduce the sidewall friction (shear strength). Rather, the application of wax, graphite, grease or lubricant oil has effect to increase the sidewall shear strength due probably to the high viscosity of such materials. Subsequently, the application of lubricants between tested soil and sidewall and neglecting the friction (shear strength) along the sidewalls may lead to inaccurate test results.

Keywords: arching, friction, laboratory tests, lubricants

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Authors: Aliakbar Golshani, Armin Ramezanzad

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Tensile strength which is an important parameter of the rock for engineering applications is difficult to measure directly through physical experiment (i.e. uniaxial tensile test). Therefore, indirect experimental methods such as Brazilian test have been taken into consideration and some relations have been proposed in order to obtain the tensile strength for rocks indirectly. In this research, to calculate numerically the tensile strength for granitic rocks, Particle Flow Code in three-dimension (PFC3D) software were used. First, uniaxial compression tests were simulated and the tensile strength was determined for Inada granite (from a quarry in Kasama, Ibaraki, Japan). Then, by simulating Brazilian test condition for Inada granite, the tensile strength was indirectly calculated again. Results show that the tensile strength calculated numerically agrees well with the experimental results obtained from uniaxial tensile tests on Inada granite samples.

Keywords: numerical simulation, particle flow code, PFC, tensile strength, Brazilian Test

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Authors: Ahmad Saadiq, Neeraj Sahu

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The partial or full replacement of natural coarse aggregate by recycled concrete aggregate (RCA) is of great benefit to the environment, as the demand of natural coarse aggregate reduces. In the modern construction and practice, the use of RCA is limited to backfilling and road construction. The establishment of RCA for its wide application can only be done after having an understanding of the use of RCA in conventional concrete. To have an insight to this, various tests to determine the compressive strength, elastic strength, workability, durability and drying shrinkage tests can be done and the test results may be different from that obtained from natural coarse aggregates, by using natural coarse aggregate in concrete. This paper gives a comprehensive review of the said tests done on RCA concrete. The results obtained from the tests indicate that RCA concrete gives comparable compressive strength, stiffness, and workability relative to the corresponding results obtained from the natural coarse aggregates. However, the durability and drying shrinkage had more variance but well within recommended limits.

Keywords: aggregate, compressive strength, durability, modulus of elasticity, recycled concrete, shrinkage, workability

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Authors: R. Alias, A. Kasa, M. R. Taha

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The effect of particle size on shear strength of granular materials are investigated using direct shear tests. Small direct shear test (60 mm by 60 mm by 24 mm deep) were conducted for particles passing the sieves with opening size of 2.36 mm. Meanwhile, particles passing the standard 20 mm sieves were tested using large direct shear test (300 mm by 300 mm by 200 mm deep). The large direct shear tests and the small direct shear tests carried out using the same shearing rate of 0.09 mm/min and similar normal stresses of 100, 200, and 300 kPa. The results show that the peak and residual shear strength decreases as particle size increases.

Keywords: particle size, shear strength, granular material, direct shear test

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Authors: Ghulam Hussain, Herrington Lee, Comfort Paul, Jones Richard

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Background: To determine the functional limitations of the lower limbs or readiness to return to sport, most rehabilitation programs use some form of testing; however, it is still unknown what the pass criteria is. This study aims to investigate the differences between the dominant and non-dominant leg performances across several lower limb tasks, which are hop tests, two-dimensional (2D) frontal plane projection angle (FPPA) tests, and isokinetic muscle tests. This study also provides the reference values for the limb symmetry index (LSI) for the hop and isokinetic muscle strength tests. Twenty recreationally active participants were recruited, 11 males and 9 females (age 23.65±2.79 years; height 169.9±3.74 cm; and body mass 74.72±5.81 kg. All tests were undertaken on the dominant and non-dominant legs. These tests are (1) Hop tests, which include horizontal hop for distance and crossover hop tests, (2) Frontal plane projection angle (FPPA): 2D capturing from two different tasks, which are forward hop landing and squatting, and (3) Isokinetic muscle strength tests: four different muscles were tested: quadriceps, hamstring, ankle plantar flexor, and hip extensor muscles. The main outcome measurements were, for the (1) hop tests: maximum distance was taken when undertaking single/crossover hop for distance using a standard tape measure, (2) for the FPPA: the knee valgus angle was measured from the maximum knee flexion position using a single 2D camera, and (3) for the isokinetic muscle strength tests: three different variables were measured: peak torque, peak torque to body weight, and the total work to body weight. All the muscle strength tests have been applied in both concentric and eccentric muscle actions at a speed of 60°/sec. This study revealed no differences between the dominant and non-dominant leg performance, and 85% of LSI was achieved by the majority of the subjects in both hop and isokinetic muscle tests, and; therefore, one leg’s hop performance can define the other.

Keywords: 2D FPPA, hop tests, isokinetic testing, LSI

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Authors: Tahar Ayadat

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The undrained shear strength is an essential parameter for determining the consistency and the ultimate bearing capacity of a clay layer. The undrained shear strength can be determined by field tests such as the in situ vane test or in laboratory, including hand vane test, triaxial, simple compression test, and the consistency penetrometer (i.e. Swedish cone). However, the field vane test and the Swedish cone are the most commonly used tests by geotechnical experts. In this technical note, a comparison between the shear strength results obtained by the in situ vane test and the cone penetration test (Swedish cone) was conducted. A correlation between the results of these two tests, concerning the undrained shear strength of the Champlain sea clay, has been developed. Moreover, some applications of the proposed correlation on some geotechnical problems have been included, such as the determination of the consistency and the bearing capacity of a clay layer.

Keywords: correlation, shear strength, clay, vane test, Swedish cone

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Authors: M. Etezadi, A. Fahimifar

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In many geotechnical designs in rocks and rock masses, tensile strength of rock and rock mass is needed. The difficulties associated with performing a direct uniaxial tensile test on a rock specimen have led to a number of indirect methods for assessing the tensile strength that in the meantime the Brazilian test is more popular. Brazilian test is widely applied in rock engineering because specimens are easy to prepare, the test is easy to conduct and uniaxial compression test machines are quite common. This study compares experimental results of direct and Brazilian tensile tests carried out on two rock types and three concrete types using 39 cylindrical and 28 disc specimens. The tests are performed using Servo-Control device. The relationship between direct and indirect tensile strength of specimens is extracted using linear regression. In the following, tensile strength of direct and indirect test is evaluated using finite element analysis. The results are analyzed and effective factors on results are studied. According to the experimental results Brazilian test is shown higher tensile strength than direct test. Because of decreasing the contact surface of grains and increasing the uniformity in concrete specimens with fine aggregate (largest grain size= 6mm), higher tensile strength in direct test is shown. The experimental and numerical results of tensile strength are compared and empirical relationship witch is obtained from experimental tests is validated.

Keywords: tensile strength, brittle materials, direct and indirect tensile test, numerical modeling

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Authors: İsmail İnce, Mustafa Fener, Sair Kahraman

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The uniaxial compressive strength (UCS) of rocks is an important input parameter for the design of rock engineering project. Compressive strength can be determined in the laboratory using the uniaxial compressive strength (UCS) test. Although the test is relatively simple, the method is time consuming and expensive. Therefore many researchers have tried to assess the uniaxial compressive strength values of rocks via relatively simple and indirect tests (e.g. point load strength test, Schmidt Hammer hardness rebound test, P-wave velocity test, etc.). Pyroclastic rocks are widely exposed in the various regions of the world. Cappadocia region located in the Central Anatolia is one of the most spectacular cite of these regions. It is important to determine the mechanical behaviour of the pyroclastic rocks due to their ease of carving, heat insulation properties and building some civil engineering constructions in them. The purpose of this study is to estimate a widely varying uniaxial strength of pyroclastic rocks from Cappadocia region by means of point load strength, porosity, dry density and saturated density tests utilizing gene expression programming.

Keywords: pyroclastic rocks, uniaxial compressive strength, gene expression programming (GEP, Cappadocia region

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Authors: Marouen Hamdi, Johannes A. Poulis

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This study investigates the impact of UV/ozone treatment on the adhesion of ethylene propylene diene methylene (EPDM) rubber, polyvinyl chloride (PVC), and acrylonitrile butadiene styrene (ABS) materials. The experimental tests consist of contact angle measurements, standardized adhesion tests, and spectroscopic and microscopic observations. Also, commonly-used surface free energy models were applied to characterize the wettability of the materials. Preliminary results show that the treatment enhances the wettability of the examined polymers. Also, it considerably improved the adhesion strength of PVC and ABS and shifted their failure modes from adhesive to cohesive, without a significant effect on EPDM. Spectroscopic characterization showed significant oxidation-induced changes in the chemical structures of treated PVC and ABS surfaces. Also, new morphological changes (microcracks, micro-holes, and wrinkles) were observed on these two materials using the SEM. These chemical and morphological changes on treated PVC and ABS promote more reactivity and mechanical interlocking with the adhesive, which explains the improvement in their adhesion strength. After characterizing the adhesion strength of the systems, accelerated ageing tests in controlled environment chambers will be conducted to determine the effect of temperature, moisture, and UV radiation on the performance of the polymeric bonded joints.

Keywords: accelerated tests, adhesion strength, ageing of polymers, UV/ozone treatment

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Authors: Xuan Sun, Mingbo Tong

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In order to study the effect of hydrothermal environment on the fatigue properties of carbon fiber fabric composites, the experiments on fatigue and residual compressive strength with the center-hole laminates were carried out. For the experiments on fatigue in hydrothermal environment, an environmental chamber used for hydrothermal environment was designed, and the FLUENT was used to simulate the field of temperature in the environmental chamber, it proved that the design met the test requirements. In accordance with ASTM standard, the fatigue test fixture and compression test fixture were designed and produced. Then the tension-compression fatigue tests were carried out in conditions of standard environment (temperature of 23+2℃, relative humidity of 50+/-5%RH) and hydrothermal environment (temperature of 70 +2℃, relative humidity of 85+/-5%RH). After that, the residual compressive strength tests were carried out, respectively. The residual compressive strength after fatigue in condition of standard environment was set as a reference value, compared with the value in condition of hydrothermal environment, calculating the difference between them. According to the result of residual compressive strength tests, it shows that the residual compressive strength after fatigue in condition of hydrothermal environment was decreased by 13.5%,so the hydrothermal environment has little effect on the residual compressive strength of carbon fiber fabric composites laminates after fatigue under load spectrum in this research.

Keywords: carbon fiber, hydrothermal environment, fatigue, residual compressive strength

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Authors: I Lamri, L Arabet, M. Hidjeb

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The direct shear test was used to determine the shear strength parameters C and Ø of a series of samples with different cement content. Samples stabilized with a certain percentage of cement showed a substantial gain in compressive strength and a significant increase in shear strength parameters. C and Ø. The laboratory equipment used in UCS tests consisted of a conventional 102mm diameter sample triaxial loading machine. Beyond 4% cement content a very important increase in shear strength was observed. It can be deduced from a comparative study of shear strength of soil samples with 4%, 7%, and 10% cement with sample containing 2 %, that the sample with a 4% cement content showed 90% increase in shear strength while those with 7% and 10% showed an increase of around 13 and 21 fold.

Keywords: cement, compression strength, shear stress, cohesion, angle of internal friction

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Authors: Jairo Alejandro Fernandez Ortega

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Objective: Regarding effects of training velocity on strength in the functional condition of older adults controversy exists. The purpose of this study was to examine the effects of a twelve-week strength training program (PE) performed at high speed (GAV) versus a traditionally executed program (GBV), on functional performance, maximum strength and muscle power in a group of older adult women. Methodology: 86 women aged between 60-81 years participated voluntarily in the study and were assigned randomly to the GAV (three series at 40% 1RM at maximum speed, with maximum losses of 10% speed) or to the GBV (three series with three sets at 70% of 1RM). Both groups performed three weekly trainings. The maximum strength of upper and lower limbs (1RM), prehensile strength, walking speed, maximum power, mean propulsive velocity (MPV) and functional performance (senior fitness test) were evaluated before and after the PE. Results: Significant improvements were observed (p < 0.05) in all the tests in the two groups after the twelve weeks of training. However, the results of GAV were significantly (P < 0.05) higher than those of the GBV, in the tests of agility and dynamic equilibrium, stationary walking, sitting and standing, walking speed over 4 and 6 meters, MPV and peak power. In the tests of maximum strength and prehensile force, the differences were not significant. Conclusion: Strength training performed at high speeds seems to have a better effect on functional performance and muscle power than strength training performed at low speed.

Keywords: power training, resistance exercise, aging, strength, physical performance, high-velocity, resistance training

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Authors: D. Jagath Kumari, K. Srinivasa Rao

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Quality assurance of the structures subjected to high temperatures is now enforcing measure for the Structural Engineers. The existing relations between strength and nondestructive measurements have been established under normal conditions are not suitable to concretes that have been exposed to high temperatures. The scope of the work is to investigate the influence of high temperatures of short durations on the residual properties of reinforced HVFA concrete columns that affect the strength by non-destructive tests (NDT). Fly ash concrete is increasingly used in the design of normal strength, high strength and high performance concretes. In this paper, the authors revealed the influence of high temperatures on HVFA concrete columns. These columns are heated from 100oC to 800oC with increments of 100oC and allowed to cool to room temperature by two methods one is air cooling method and the other immediate water quenching method. All the specimens were tested identically, before heating and after heating for compressive strength and material integrity by rebound hammer and ultrasonic pulse velocity (UPV) meter respectively. HVFA concrete retained more residual strength by water quenching method than air-cooling method.

Keywords: HVFA concrete, NDT methods, residual strength, non-destructive tests

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Authors: Nimesh D. Chaudhari

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The purpose of this study was to find out the interrelationship of BMI with strength, i.e. endurance strength of abdominal muscles and explosive strength of leg muscles, speed and flexibility which are respectively assessed by sit up, standing broad jump, 50 yard dash and sit and reach tests. 48 boys, aged 7 to 13 years as group A and 40 boys, aged 17 to 28 years asgroup B were selected as the subjects for the study. Product moment correlation coefficient test (r at 0.05 level of significance) was applied to test hypothesis. The findings of the study shows that there is significant relationship of BMI with endurance strength of abdominal muscles, explosive strength of leg muscles, and flexibility whereas a negative significant relationship was found between BMI and speed in group A, i.e. aged from 7 to 13 years. However, there was no significant relationship of BMI with endurance strength of abdominal muscles, explosive strength of leg muscles, speed and flexibility in higher age group.

Keywords: body mass index, strength of abdominal muscles, explosive strength of leg muscles, flexibility of lower back and hamstring muscles

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Authors: Elie Awwad, Bilal Hamad, Mounir Mabsout, Helmi Khatib

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The paper reports test results on the long-term behavior of sustainable hemp-concrete material prepared in research work conducted at the American University of Beirut. The tests results are in terms of compressive and splitting tensile tests conducted on standard 150x300 mm cylinders. A control mix without fibers, one polypropylene-concrete mix, and ten hemp-concrete mixes were prepared with different percentages of industrial hemp fibers and reduced coarse aggregate contents. The objective was to investigate the strength properties of hemp-reinforced concrete at 1.5 years age as compared with control mixes. The results indicated that both the compressive strength and the splitting tensile strength results of all tested cylinders increased as compared with the 28-days values. Also, the difference between the hemp-concrete samples and the control samples at 28 days was maintained at 1.5 years age indicating that hemp fibers did not exhibit any negative effect on the long-term strength properties of concrete.

Keywords: hemp-reinforced concrete, natural fibers, compressive strength, splitting tensile strength

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Authors: Ayad Salih Sabbar, Amin Chegenizadeh, Hamid Nikraz

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Utilizing waste materials in civil engineering applications has a positive influence on the environment by reducing carbon dioxide emissions and issues associated with waste disposal. Granulated blast furnace slag (GBFS) is a by-product of the iron and steel industry, with millions of tons of slag being annually produced worldwide. Slag has been widely used in structural engineering and for stabilizing clay soils; however, studies on the effect of slag on sandy soils are scarce. This article investigates the effect of slag content on shear strength parameters through direct shear tests and unconsolidated undrained triaxial tests on mixtures of Perth sand and slag. For this purpose, sand-slag mixtures, with slag contents of 2%, 4%, and 6% by weight of samples, were tested with direct shear tests under three normal stress values, namely 100 kPa, 150 kPa, and 200 kPa. Unconsolidated undrained triaxial tests were performed under a single confining pressure of 100 kPa and relative density of 80%. The internal friction angles and shear stresses of the mixtures were determined via the direct shear tests, demonstrating that shear stresses increased with increasing normal stress and the internal friction angles and cohesion increased with increasing slag. There were no significant differences in shear stresses parameters when slag content rose from 4% to 6%. The unconsolidated undrained triaxial tests demonstrated that shear strength increased with increasing slag content.

Keywords: direct shear, shear strength, slag, UU test

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Authors: H. I. Beloufa, M. Tarfaoui

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For many applications, adhesively bonded assemblies have gained an increasing interest in the industry due to several advantages over welding, riveting and bolting, such as reduction of stress concentrations, lightness, low cost and easy manufacturing. This work is largely concerned to show the effects of the loading rate of the adhesively bonded joints under different speed rates. The tensile tests were conducted at four different rates; static (5mm/min, 50mm/min) and dynamic tests (1m/s, and 10m/s). An attempt was made to determine the damage kinetic and a comparison between the use of aluminium and composite laminate substrates is introduced. Aluminum T6082 and glass/vinylester laminated composite Substrates were used to construct aluminum/aluminum and laminate/laminate specimens. The adhesive used in this study was Araldite 2015. The results showed the effects of the loading rate évolution on the double joint strength. The comparison of the results of static and dynamic tests showed a raise of the strength of the specimens while the load velocity is elevated. In the case of composite substrates double joint lap, the stiffness increased by more than 60% between static and dynamic tests. However, in the case of aluminum substrates, the rigidity improved about 28% from static to moderately high velocity loading. For both aluminum and composite double joint lap, the strength increased by approximately 25% when the tensile velocity is increased from 5 mm/min to 50 mm/min (static tests). Nevertheless, the tensile velocity is extended to 1m/s the strength increased by 13% and 25% respectively for composite and aluminum substrates.

Keywords: adhesive, double lap joints, static and dynamic behavior, tensile tests

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Authors: Waheed Ahmad Safi, Shunichi Nakamura

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Steel/concrete composite bridge with the concrete filled steel I-girder (CFIG) was proposed, and the bending and shear strength was studied by experiments and FEM analysis. The area surrounded by the upper and lower flanges and the web is filled with concrete in CFIG, which is used at the intermediate support of a continuous girder. The bending and shear tests of the CFIG were carried out, showing that the bending strength of CFIG was 2.8 times of the conventional steel I-girder and the shear strength was 3.0 times of the steel I-girder. Finite element models were established to clarify bending and shear behaviors and the load transfer mechanism of CFIG. FEM result agreed very well with the test results. The FEM model was also applied to simulate the shear tests of the CFIG specimens. A trail design was carried out for a four-span continuous highway bridge and the design method was established.

Keywords: bending strength, concrete filled steel I-girder, steel I-girder, FEM, limit states design and shear strength

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Authors: Henok Marie Shiferaw, Barbara Schneider-Muntau

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Test repeatability and data reproducibility are a concern in many geotechnical laboratory tests due to inherent soil variability, inhomogeneous sample preparation and measurement inaccuracy. Test results on comparable test specimens vary to a considerable extent. Thus, also the derived shear strength parameters from triaxial tests are affected. In this contribution, we present the reproducibility of effective shear strength parameters from consolidated undrained triaxial tests on plain soil and cement-treated soil specimens. Six remolded test specimens were prepared for the plain soil and for the cement-treated soil. Conventional three levels of consolidation pressure testing were considered with an effective consolidation pressure of 100 kPa, 200 kPa and 300 kPa, respectively. At each effective consolidation pressure, two tests were done on comparable test specimens. Focus was laid on the same mean dry density and same water content during sample preparation for the two specimens. The cement-treated specimens were tested after 28 days of curing. Shearing of test specimens was carried out at a deformation rate of 0.4 mm/min after sample saturation at a back pressure of 900 kPa, followed by consolidation. The effective peak and residual shear strength parameters were then estimated from regression analysis of 21 different combinations of the failure stresses from the six tests conducted for both the plain soil and cement-treated soil samples. The 21 different stress combinations were constructed by picking three, four, five and six failure tresses at once at different combinations. Results indicate that the effective shear strength parameters estimated from the regression of different combinations of the failure stresses vary. Effective critical friction angle was found to be more consistent than effective peak friction angle with a smaller standard deviation. The reproducibility of the shear strength parameters for the cement-treated specimens was even lower than that of the untreated specimens.

Keywords: shear strength parameters, test repeatability, data reproducibility, triaxial soil testing, cement improvement of soils

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Authors: Najibullah Arsalan, Masaru Akaishi, Motohiro Sugiyama

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When constructing a structure on soft rock, adequate research and study are required concerning the shear behavior in the over-consolidation region because soft rock is considered to be in a heavily over-consolidated state. In many of the existing studies concerning the strength of soft rock, triaxial compression tests were conducted using isotropically consolidated samples. In this study, the strength of diatomaceous soft rock anisotropically consolidated under a designated consolidation pressure is examined in undrained triaxial compression tests, and studies are made of the peak and residual strengths of the sample in the over-consolidated state in the initial yield surface and the anisotropic yield surface.

Keywords: diatomaceouse mudstone, shear strength, yield surface, triaxial compression test

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Authors: Dogan Cetin, Omar Hamdi Jasim

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Using some additives is very common method to improve the soil properties such as shear strength, bearing capacity; and to reduce the settlement and lateral deformation. Soil reinforcement with natural materials is an attractive method to improve the soil properties because of their low cost. However, the studies conducted by using natural additive are very limited. This paper presents the results of an investigation on the immediate and long-term effects of the sawdust on the shear strength behavior of a clayey silt soil obtained in Arnavutkoy in Istanbul with sawdust. Firstly, compaction tests were conducted to be able to optimum moisture content for every percentage of sawdust. The samples were obtained from compacted soil at optimum moisture content. UU Triaxial Tests were conducted to evaluate the response of randomly distributed sawdust on the strength of low plasticity clayey silt soil. The specimens were tested with 1%, 2% and 3% content of sawdust. It was found that the undrained shear strength of clay soil with 1%, 2% and 3% sawdust were increased respectively 4.65%, 27.9% and 39.5% higher than the soil without additive. At 5%, shear strength of clay soil decreased by 3.8%. After 90 days cure period, the shear strength of the soil with 1%, 2%, 3% and %5 increased respectively 251%, 302%, 260% and 153%. It can be said that the effect of the sawdust usage has a remarkable effect on the undrained shear strength of the soil. Besides the increasing undrained shear strength, it was also found that the sawdust decreases the liquid limit, plastic limit and plasticity index by 5.5%, 2.9 and 10.9% respectively.

Keywords: compaction test, sawdust, shear strength, UU Triaxial Test

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Authors: G. Minak, D. Ghelli, A. Zucchelli

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This paper presents the results of an experimental characterization of a glass fibre-epoxy composite. The behavior of the traditional two-phase composite has been compared with the one of a new three-phase composite where the epoxy matrix was modified by addition of a 3% weight fraction of montmorillonite nano-particles. Two different types of nano-clays, Cloisite® 30B and RXG7000, produced by Southern Clay Products Inc., have been considered. Three-point bending tests, both monotonic and cyclic, were carried out. A strong reduction of the ultimate flexural strength upon nano-modification has been observed in quasi-static tests. Fatigue tests yielded a smaller strength loss. In both quasi-static and fatigue tests a more pronounced tendency to delamination has been noticed in three-phase composites, especially in the case of 30B nano-clay, with respect to the standard two-phase glass fiber composite.

Keywords: bending fatigue, epoxy resin, glass fiber, montmorillonite

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Authors: K. M. Aldossari, W. A. Elsaigh, M. J. Shannag

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An experimental study was conducted to investigate the effect of hooked-end steel fibers on the flexural behavior of normal and high strength concrete matrices. The fiber content appropriate for the concrete matrices investigated was also determined based on flexural tests on standard prisms. Parameters investigated include: Matrix compressive strength ranging from 45 MPa to 70 MPa, corresponding to normal and high strength concrete matrices respectively; Fiber volume fraction including 0, 0.5%, 0.76%, and 1%, equivalent to 0, 40, 60, and 80 kg/m3 of hooked-end steel fibers respectively. Test results indicated that flexural strength and toughness of normal and high strength concrete matrices were significantly improved with the increase in the fiber content added; Whereas a slight improvement in compressive strength was observed for the same matrices. Furthermore, the test results indicated that the effect of increasing the fiber content was more pronounced on increasing the flexural strength of high strength concrete than that of normal concrete.

Keywords: concrete, flexural strength, toughness, steel fibers

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Authors: Sujeet Kumar, Arun Prasad

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The present work investigates the effect of multiple parameters on the unconfined compressive strength of the bauxite residue-lime mix. A number of unconfined compressive strength tests considering various curing time, lime content, dry density and moisture content were carried out. The results show that an empirical correlation may be successfully developed using volumetric lime content, porosity, moisture content, curing time unconfined compressive strength for the range of the bauxite residue-lime mix studied. The proposed empirical correlations efficiently predict the strength of bauxite residue-lime mix, and it can be used as a generalized empirical equation to estimate unconfined compressive strength.

Keywords: bauxite residue, curing time, porosity/volumetric lime ratio, unconfined compressive strength

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Authors: A. Mudau, T. R. Stacey, R. A. Govender

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This paper reports for the first time the findings on the dynamic compressive strength data of Bushveld Complex brittle rock materials. These rocks were subjected to both quasi-static and impact loading tests to help understand their behaviour both under quasi-static and dynamic loading conditions. Unlike quasi-static tests, characterization of dynamic behaviour of materials is challenging, in particularly brittle rock materials. The split Hopkinson pressure bar (SHPB) results reported for anorthosite and norite showed relatively low values for dynamic compressive strength compared to the quasi-static uniaxial compressive strength data. It was noticed that the dynamic stress conditions were not fully attained during testing, as well as constant strain rate.

Keywords: Bushveld Complex, dynamic comperession, rock brittleness, stress equilibrium

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Authors: P. Cavlan, B. Kırmızıgil

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Introduction: Each exercise in suspension exercises offer the use of gravity and body weight; and is thought to develop the equilibrium, flexibility and body stability necessary for daily life activities and sports, in addition to creating the correct functional force. Suspension exercises based on body weight focus the human body as an integrated system. Total Resistance Exercises (TRX) suspension training that physiotherapists, athletic health clinics, exercise centers of hospitals and chiropractic clinics now use for rehabilitation purposes. The purpose of this study is to investigate and compare the effects of TRX suspension exercises on physical performance in healthy individuals. Method: Healthy subjects divided into two groups; the study group and the control group with 40 individuals for each, between ages 20 to 45 with similar gender distributions. Study group had 2 sessions of suspension exercises per week for 8 weeks and control group had no exercises during this period. All the participants were given explosive strength, flexibility, strength and endurance tests before and after the 8 week period. The tests used for evaluation were respectively; standing long jump test and single leg (left and right) long jump tests, sit and reach test, sit up and back extension tests. Results: In the study group a statistically significant difference was found between prior- and final-tests in all evaluations, including explosive strength, flexibility, core strength and endurance of the group performing TRX exercises. These values were higher than the control groups’ values. The final test results were found to be statistically different between the study and control groups. Study group showed development in all values. Conclusions: In this study, which was conducted with the aim of investigating and comparing the effects of TRX suspension exercises on physical performance, the results of the prior-tests of both groups were similar. There was no significant difference between the prior and the final values in the control group. It was observed that in the study group, explosive strength, flexibility, strength, and endurance development was achieved after 8 weeks. According to these results, it was shown that TRX suspension exercise program improved explosive strength, flexibility, especially core strength and endurance; therefore the physical performance. Based on the results of our study, it was determined that the physical performance, an indispensable requirement of our life, was developed by the TRX suspension system. We concluded that TRX suspension exercises can be used to improve the explosive strength and flexibility in healthy individuals, as well as developing the muscle strength and endurance of the core region. The specific investigations could be done in this area so that programs that emphasize the TRX's physical performance features could be created.

Keywords: core strength, endurance, explosive strength, flexibility, physical performance, suspension exercises

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Authors: Siti Nur Afifah Azraai, Lim Kar Sing, Nordin Yahaya, Norhazilan Md Noor

Abstract:

This experimental study consists of a characterization of epoxy grout where an amount of 2% of graphene nanoplatelets particles were added to commercial epoxy resin to evaluate their behavior regarding neat epoxy resin. Compressive tests, tensile tests and flexural tests were conducted to study the effect of graphene nanoplatelets on neat epoxy resin. By comparing graphene-based and neat epoxy grout, there is no significant increase of strength due to weak interface in the graphene nanoplatelets/epoxy composites. From this experiment, the tension and flexural strength of graphene-based epoxy grouts is slightly lower than ones of neat epoxy grout. Nevertheless, the addition of graphene has produced more consistent results according to a smaller standard deviation of strength. Furthermore, the graphene has also improved the ductility of the grout, hence reducing its brittle behaviour. This shows that the performance of graphene-based grout is reliably predictable and able to minimize sudden rupture. This is important since repair design of damaged pipeline is of deterministic nature.

Keywords: composite, epoxy resin, graphene nanoplatelets, pipeline

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Authors: Lubov Magerramova, Vladimir Isakov, Michail Petrov

Abstract:

A methodology for calculating and modeling technological modes of laser 3D printing of Ti6Al4V powder alloy samples has been developed. ProXDPM320 3D printer was used. The technological model that takes into account the multifactorial influence of modes and conditions of additive cultivation on characteristics and strength properties of titanium samples has been created. Process control parameters and an order parameter, to which the others are subordinate, were established. Using the iterative method, the optimal technological parameters for the additive growth of cylindrical samples were calculated. The calculations were combined with data obtained during virtual 3D printing in the Altair Inspire software environment. The samples were subjected to short-term tensile strength tests at normal temperature on a servo-hydraulic machine “LFV-100”. As a result, deformation diagrams were constructed, and mechanical characteristics such as proportionality limit, conditional yield strength, tensile strength, elastic modulus, relative elongation, and stress at break were obtained. Comparison of these characteristics with those for the industrial alloy Ti6Al4V showed acceptable agreement. Some of the synthesized samples were subjected to laser shock treatment to increase fatigue strength. The results obtained were used to validate the mathematical model of 3D printing of titanium alloys.

Keywords: additive technology, titanium alloy, numerical simulation, strength tests

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