Papers by Keyword: Strain Rate

Abstract: Research on the dynamic strength of various materials such as metallic materials, polymers, concrete has been done by many researchers. The Split Hopkinson Bar method is still used to produce a high strain rate. In this method, a striker bar is usually launched using pressurized gas. However, high security system is required to prevent leakage as the operating pressure is very high. Avoiding the use of high-pressure gas, in this study, a mechanical system of springs used to propel the Striker Bar. By varying the spring deflection of 1 cm to 8 cm, a linear Striker Bar velocity from 2.17 m/s until 19.45 m/s is obtained. Aluminum alloy Al-2024 has been tested with this tool and it is found that at the maximum Striker Bar velocity, strain rate on the material can be reach 1132 s^-1, and dynamic compression yield strength increase 56% from quasi-static compression yield strength.

Abstract: The technique of recording the changes in the dynamic deformation field of non-equilibrium processes in the alloys of aluminum. It was established experimentally that the structural changes are implemented in the propagation of elastic waves in the material deformation. Qualitatively be characterized distribution of high plasticity surface of the specimen and determined its size after realization of dynamic non-equilibrium processes.

Abstract: Concrete structure in reality mostly in complicated stress state, dynamic characteristics and static characteristics under earthquakes and other dynamic loads are very different. For a further understanding of the dynamic characteristics of the concrete, true triaxial testing machine system was used to the C30 concrete at different strain rates and different side of the cube concrete specimens stress biaxial dynamic compression tests. Biaxial stress state concrete elasticity modulus, peak stress, peak strain, was obtained by the experimental study, and carries on the comparative analysis. Results show that: the dynamic characteristics of concrete under biaxial compression state of concrete and uniaxial condition are very different.

Abstract: Composite materials are widely used in aircraft, automotive, marine and railway applications and are exposed to impact loads, in particular low velocity impact. As material properties of composites are affected by strain-rate [, finite element analysis (FEA) by using static properties would not predict their impact behaviour accurately. Thus, the objective of this study was to include strain-rate effects in the simulation of composite laminates under low velocity impact. This was achieved using ABAQUS anisotropic damage model (ADM) by taking account of material properties changes as a function of log strain-rate using user-defined ABAQUS/VUSDFLD subroutine Strain-Rate Dependent ADM (SRD ADM). Results obtained from SRD ADM were validated using simple tensile test done by Okoli [. Subsequently a three-point bending impact event of a simple composite laminate beam by a cylindrical steel impactor was simulated using both the original ABAQUS Static ADM and the user-defined SRD ADM, and compared with experimental impact test results done by [. The results show that reductions in errors of predicted maximum impact reaction force (compared to experimental data) were achieved from 29% using Static ADM to 14% using SRD ADM and from 35% using Static ADM to 15% using SRD ADM respectively for impactor speeds of 2 ms^-1 and 5 ms^-1.

Abstract: Advanced polymeric materials, such as ultra-high molecular weight polyethylene (UHMWPE) are used in lightweight body armour because of their combination of good impact resistance with light weight. However, a broader use of such materials is limited by the complexity and cost of the manufacturing processes and the lack of experimental data on their behaviour and failure evolution under high strain-rate loading conditions. The current study deals with an investigation of the internal heat generation during the tensile testing of UHWMPE and polymer nano-composite blends at various strain rates. A 3D finite element (FE) model of the tensile test is developed and validated with the experimental work. An elastic-plastic material model is used with adiabatic heat generation. The temperature and stresses obtained with the FE analysis are found to be in a good agreement with the experimental results for UHMWPE materials. The model can be used as a simple and cost effective tool to predict the thermo-mechanical behaviour of parts made from these materials under various loading conditions.

Abstract: The tensile properties of alloy steel 35CrMoA were measured by dynamic tension experimental apparatus, and the stress-strain curves of the material at strain rate range from 10^-2/s to 10³/s were obtained. The fracture appearance and metallurgical structure were observed for the recovered specimens. The influence of strain rates on mechanical properties and microstructure of the 35CrMoA steel was analyzed. Based on the experimental data of mechanical properties, the JC constitutive parameters were fitted for 35CrMoA.

Abstract: An improved dynamic constitutive model is presented, aiming to describe the key mechanical properties and predict the bearing strength of concrete structure under static and dynamic load. This model is based on the concept of equivalent uniaxial strains and strain rate. In this paper, an equivalent uniaxial stressstrain curves are obtained by the WillamWarnke curve and take the same form as in Saenz models. Then, the bending strength of a concrete beam under different static and dynamic load was discussed.

Abstract: In this study, the local stress of unidirectional fiber reinforced marine composites under transverse direction tension is conducted by using a representative volume element (RVE). With the application of fracture mechanics theory, the strength and debonding evolution of the fibre-matrix interface is analyzed and simulated by cohesive elements in FEA. The modeling results fit the experimental results in quasi-static conditions well, which demonstrates a proper simulation method for assessing the transverse mechanical properties of marine composites. Considering the complex work environment in ocean, transverse mechanical behaviors of marine composites under different strain rates is investigated, which would provide guidance for the marine composite designers.

Abstract: River ice exists in the most countries and regions and brings much damage to the structures in the river. However, the mechanical properties of the river ice are still unclear. In the present study, over 150 specimens of river ice taken from Songhua River of China have been investigated using the MTS machine to measure the flexural strength and the effective modules at various test temperature and strain rate. The test temperature was set at three different point (-5°C,-10°C,-20°C), the strain rate was set at the range from 3.33E-5/S to 3.33E-3/S. The test results show that the flexural strength of river ice depends on the temperature and strain rate. It increases with the decreasing test temperature. The flexural strength of river ice changes at the various strain rate, however, it is non-monotonic. The variation curve looks like a inversed "W" shape. Under flexural loading condition, the effective modules of Songhua River ice is about 0.568~0.825GPa. And The modules of river ice increases with the increasing of the strain rate. The effective modules of river ice also increases with the decreasing of the test temperature slightly.

Abstract: Taylor impact tests are used as experimental and numerical tests for determining the mechanical behavior of materials subjected to high strain rates. Taylor impact tests are numerically simulated in the velocity range from 150m/s to 250m/s. Deformations of different impact velocity; impact damages of the axis centre; and the reasons of impact damage are discussed in the numerical simulation of Taylor impact test.