Papers by Keyword: Strain Rate Effect

Abstract: Controlled chip breakage is important for machining process. In order to investigate the chip breakage behaviour in turning process, damage mechanics approach is applied in FE simulation of chip breakage. In this work, an advanced damage mechanics model is implemented for description of the plastic flow and damage behaviour of chip material in simulation. This material model takes the temperature, strain rate as well as state of stress into consideration, which are essential for application in machining processes.

Abstract: The high strength steel which was subjected with isothermal heat treatment at three different temperatures, namely 330°C, 350°Cand 380°C after different quenching temperature namely 880°C and 900°C,was investigated in this paper. The quasi-static and dynamic mechanical properties of new high strength steel was tested by universal material testing machine and Split Hopkinson Pressure Bar (SHPB). Experimental results have showed that the yield strength and tensile strength of the steel reach 1100MPa and 1400MPa respectively. Hardness, yield strength and toughness are found to decrease with the consequently increasing of isothermal temperature under the same quenching temperature. The compression properties of the steel under quenching temperature of 880°C are higher than that of 900°C with the same isothermal temperature. It can be found that the steel which is subjected with isothermal heat treatment show strain rate sensitivity under high velocity impact. When isothermal temperature is set 380°C, the steel exhibits the most obvious strain rate hardening effect.

Abstract: High-speed tensile tests were carried out to investigate strain rate effect on both yield stress and failure strain using ASTM D1822 Type-S specimens made of polycarbonate. Based on test results, parameters for a material model suitable for polymers are determined, and numerical analysis is carried out to simulate test results. The material model is used to simulate tensile test using a dog-bone specimen and Charpy test other than the tensile test of Type-S specimens. It is found that good predictions can be obtained when rate dependent material parameters are used. Further, the high-speed tensile test considered in the present study is suitable for selection of parameters for material modeling of polymers for impact analysis.

Abstract: Austenitic stainless steel was compressed at a strain rates of 10³ s^-1 using a Hopkinson pressure bar apparatus at temperatures of 77 K and 293 K. The electrical resistivity was measured to determine the volume fraction of martensite of a deforming specimen. A compressive specimen of the dumbbell type was suitable for attaching the lead-in wires of four-point probes to the specimen. The volume fraction of martensite formed at a strain rate of 10³ s^-1 was lower than that formed at a low strain rate regardless of the temperature, and the effect of the strain rate on the electrical resistivity was slight. However, since the volume fraction of martensite is expressed as a linear function of the electrical resistivity ratio as well as in the results obtained by the tensile test, the electrical resistivity was available as an index for estimating the volume fraction of martensite induced by dynamic deformation. The duration of the input wave was approximately 150 μs, and the appearance of the peak value of transient resistivity was approximately 1ms after the arrival of the input wave at the specimen. These results showed that the structure change evaluated using electrical resistivity was not completed in the time required for the stress wave to pass through the specimen, although the electrical resistivity immediately after dynamic deformation closely approached that obtained by the static test.

Abstract: In this study, a finite element model is developed for simulation of the structural behaviour of steel-reinforced concrete panels under blast loading using LS-DYNA. Pure Lagrangian formulation is applied in the finite element analysis, and the strain rate effect is taken into account in the material models of both concrete and steel. The finite element model is validated by comparing the computed results with experimental test results from the literature. Structural behaviour of concrete panel with different parameters under blast loading is also investigated. Keywords: Blast resistance; Finite element model; Reinforced concrete panel; Strain rate effect

Abstract: Under launch impact load, LIGA nickel that manufacturing MEMS fuze safety and arming (S&A) device will have obvious strain rate effect. By using finite element analysis software ANSYS/LS-DYNA, simulation models of a small-caliber ammunition MEMS fuze setback S&A device with strain rate effect and without strain rate effect were respectively established. The results of the two simulation modules were quite different. Comparisons between experimental results and simulation results show that simulation results considering strain rate effect agree well with experimental results, which proves strain rate effect should not be ignored in the simulation of MEMS S&A device.

Abstract: In this paper, the dynamic compression-shear experiments on the closed-cell aluminum foam with porosity of 72%-92% are carried out by using improved split Hopkinson pressure bar. A high speed camera is used to observe the dynamic deformation behavior of the samples on the compression-shear loading. A finite element software ABAQUS is employed to simulate the dynamic compression-shear process of closed-cell aluminum foam. The results demonstrate that there is a compression-shear band on the samples during the compression-shear loading. The most severely damaged area of the material is on the compression-shear band; Low-porosity closed-cell aluminum foam has significant strain rate effect, however high-porosity closed-cell aluminum foam can ignore the strain rate effect. The yield stress of samples decreases with increasing samples angle, whereas shear stress increase with increasing samples angle, and also the corresponding time when the samples just begin to yield decreases with increasing samples angle.

Abstract: The damage and failure of reinforced concrete (RC) slabs under blast loadings may cause significant hazards for frame systems even progressive collapse of whole structures. The numerical simulation of one-way RC slabs using the finite element explicit code LS-DYNA to estimate the dynamic response and failure mode of one-way RC slabs .Blast loadings are imposed on the top surface of slabs using a blast model based on conwep algorithm. Concrete was modeled using a concrete damage constitutive model considering strain rate effect, and reinforcement was modeled using a elastoplastic material type with kinematic hardening and strain rate effect. The numerical model is introduced in details and adopted to simulate the dynamic responses of RC slabs in reference test. The numerical model can match well with the test data, and thus the proposed numerical model can be considered as a valuable tool in assessing the deformation or failure mechanism and predicting the dynamic responses of one-way RC slabs subjected to blast loadings.

Abstract: This paper is concerned with the material behaviors of PBX(Polymer Bonded eXplosive) simulant at various strain rates ranging from 0.0001/sec to 3150/sec. Material behaviors of PBX at the high strain rates are important in the prediction of deformation modes of PBX in a warhead which undergoes severe impact loading. Inert PBX stimulant which has analogous material behaviors with PBX was utilized for material tests due to safety issues. Uniaxial compressive tests at quasi-static and intermediate strain rates were conducted with cylindrical specimen using a dynamic materials testing machine, INSTRON 8801. Uniaxial compressive tests at high strain rates ranging from 1200/sec to 3150/sec were conducted using a split Hopkinson pressure bar. Deformation behaviors were investigated using captured images obtained from a high-speed camera. The strain hardening behaviors of PBX simulant were formulated by proposed strain rate-dependent strain hardening model.

Abstract: This paper presents the results of the numerical simulation of the 1993 terrorist attack at the New York World Trade Center. Aim of this work is to compare the results of the simulation with the actual damage suffered by the structure, in order to discuss and explore the possibility of extending the use of such simulation tools (widely used for industrial products) also to the design and optimization of large structures.The work involves the state of art in numerical simulation (based on finite elements method) coupled with modeling the high strain-rate effect on mechanical behavior of materials.The results show a strong concordance with the historical data of the event. This leads tohypothesize future scenarios (even normative ones) in the field of large structures design and safety improvement against impulsive events.