Papers by Keyword: Loading Rate

Abstract: . A primary current focus in concrete shear design is how to ensure the shear resistance of the concrete structures to withstand the possible adverse creep effects during the service life. All shear-carrying actions are supposed to depreciate due to the enhanced critical shear cracks under sustained loads. However, only a few studies that evaluated the performance of concrete structures failing in shear due to long-term loading. As the longitudinal tensile reinforcement strain influences the shear strength of RC beam, the shear resistance of the beam under sustained load may also be affected by the amount of longitudinal reinforcement. The present study aims at investigating the influence of flexural reinforcement ratio on the shear creep failures of reinforced concrete (RC) beams without stirrups by non-linear finite element analysis. In this study, the numerical model of RC beams with reinforcement ratios varying from 0.4% to 3.2% was evaluated under different loading rates. A loading rate of 1000 and 10000 times slower than the static loading rate were adopted to reveal the creep effects of RC beams.

Abstract: Molecular dynamics (MD) simulations of metal-metallic glass (Al-Cu₅₀Zr₅₀) multilayer during nanoindentation is carried out to investigate the load-displacement response, mechanical properties and deformation mechanisms. The indentation study is carried out at temperatures in the range of cryogenic to room temperature (10 K-300 K). The indenter speeds are varied between 0.5-5 Å/ps to study the effect of loading rate. The interaction between Al-Cu-Zr atoms are defined by EAM (Embedded Atom Method) potential. A sample size of 200 Å × 200 Å × 200 Å (in x y z-direction) comprising of 538538 atoms is used for nanoindentation. P P S boundary condition (BC) in x y z direction and NVT ensemble are used. We observed a peak load of 117 nN, at a temperature of 10 K with a loading rate of 5 Å/ps. We found that as the loading rate increase, the peak load also increases. As anticipated, the increase in temperature decreases the strength of the multilayer. The atomic displacement vector plots reveal that MG act as hurdles to the movement of dislocations nucleated at the interface.

Abstract: The spherical indentation combined with acoustic emission was used to evaluate the local strength of glass, which is a nondestructive testing approach. However, stress time effect on the local strength of glass during spherical indentation has not been studied before. In the present work, stress time effect was investigated by examining the local strength of unstrengthened and strengthened glass at different loading rates. It is discovered that the local strength of glass increased greatly with the loading rate, which confirmed the time dependence of the fracture on glass. As a typical brittle material, the discreteness of strength date of glass measured by spherical indentation was also analyzed to evaluate the strength of glass correctly.

Abstract: In this study, the influence of sheet thickness, loading rate, and punch diameter on the bending behaviour of twin-roll cast, rolled and heat-treated AZ31 magnesium alloy was investigated. Therefore, the 3-point bending test was performed at room temperature using an electromechanical testing machine (v = 0.1−10 mm/s) with different punch diameters (D = 2 mm, 8 mm, 16 mm). The initial material has a recrystallized microstructure with grain sizes of 6−9 µm. It is shown by the mechanical investigations that the bending force increases with the sheet thickness. In contrast to this, the bending angle is independent of the sheet thickness. In addition, the punch diameter and the loading rate do not influence the maximum force and the bending angle significantly.

Abstract: The essential work of fracture (EWF) method is gaining attention for the toughness evaluation of ductile polymers. However its establishment as a toughness criteria requires that the parameters influencing it and their extent of influence be identified. In the current study the effect of the loading rate on the EWF of pure polypropylene (PP) is investigated. Tensile tests are performed at room temperature on DENT samples with ligament lengths of 7 to 15 mm at loading rates of 2 to 32 mm/min. The results confirm the dependency of the EWF on the loading rate, though a regular trend is not observed. The nonregularity of the EWF on the loading rate is explained by the ligament dependency of the loading rate effect on the specific work of fracture. This study reveals that the similarity of the ligament lengths and loading rate are necessities to yielding comparable values of the EWF.

Abstract: Magnesium and its alloys have high potential for lightweight applications in the automotive and aerospace industries. In order to design parts for new applications with optimized mechanical properties and higher, more economic production rates, the forming limit behaviour of thin sheets (t < 1.0 mm) has to be known for different temperatures and loading rates. In this study, forming limit curves of 0.8 mm thick AZ31 sheet were measured for deformation at 200 °C and 250 °C and at loading rates of 1 mm/s and 10 mm/s with the Nakajima test. The investigations showed that an increase in temperature from 200 °C to 250 °C tends toward higher forming limit values for all stress states. In contrast, an increase in the loading rate from 1 mm/s to 10 mm/s induces a reduction in formability. It can be seen that the temperature, loading rate, and stress state influence the force-distance curves, the distribution of the local major strains, and the sheet thickness reduction.

Abstract: Kenaf natural fibre has become the subject of interest for a wide range of engineering sectors due to its biodegradable and outstanding mechanical properties. In this study, the effect of loading rate on the indentation behaviour of fibre metal laminates (FMLs) based on kenaf/epoxy subjected to static indentation loading was investigated. The fibre metal laminates were made of chopped strand mat (CSM) kenaf fibre with epoxy resin composite and 0.6 mm thickness of 1100-O aluminium alloy sheet by using vacuum infusion process (VIP) and hydraulic pressing technique. The experiments were conducted by using a universal testing machine with loading rate of 1 mm/min, 10 mm/min and 100 mm/min. The results of indentation resistance, energy absorption and corresponding indentation failure mechanisms were compared and discussed in this study. For 2/1 FMLs, the maximum contact force increased when the loading rate increased. The loading rate did not affect the indentation failure mechanisms of the 2/1 FMLs. However, for 3/2 FMLs, delamination occurred when the specimens were indented with loading rate of 10 mm/min.

Abstract: For studying on the effects of loading rate on modulus and strength of sandstone, uniaxial compression experiment of the samples, from Balikun mine, was performed at different loading rates. The influence of loading rate on average modulus, uniaxial compressive strength and post-peak strength degradation angle was analyzed, and the results indicate that:: The average modulus of sandstone samples increases with loading rate increasing; the both almost obey linear relationship. The peak strength of sandstone grows with the increase of loading rate; there is an approximately exponential relationship between the two. With loading rate increasing, the post-peak strength degradation angle decreases; the relationship between the both is approximately exponential.

Abstract: Effect of loading rate on bond property between corroded concrete and steel bar are studied. Simulation test and finite element are used to study the pull-out test of corroded reinforcement concrete members in present literature. Considering the corrosion of steel bar and concrete and their rate dependent characteristics, the bond property of corroded reinforcement and concrete under the different loading rate (10^-4 s^-1-10^-2 s^-1) are studied. It concluded that the bond property was improved when the rating rate form 10^-4 s^-1 to the static load; the bond property would decreased when the loading rate reached the fixed value (10^-3s^-1-10^-2s^-1), the members was failed under the smaller load.

Abstract: The aim of this study was to investigate the dynamic shear failure behavior of RC beams under rapid loading through an experimental study and also to set up a strut-and-tie model with loading rate effect to predict the dynamic shear resistance of RC beams. Thus, rapid loading test with 24 RC beams with a shear span-to-deep ratio of 1.9 was performed, in which shear reinforcement ratio and loading rate were variable. All of the RC beams exhibited shear compression failure. Although the shear resistance increases with increasing loading rate, the influence of loading rate on the shear resistance clearly depends on shear reinforcement ratio. The strut-and-tie model with loading rate effect was finally developed, in which the thickness of the compression strut was formulated to be increased with an increase in loading rate. The developed strut-and-tie model was good agreement with the experimental results.