High Strain Rate Deformation Behavior Research Articles

High strain rate deformation behavior of an AZ91 magnesium alloy at elevated temperatures

Abstract High-temperature compressive properties at a high strain rate of 103 s−1 were examined in solution treated AZ91 magnesium alloy. Analysis of the flow behavior and microstructural observations indicated that the deformation at high strain rates of ∼103 s−1 proceeds by conventional plastic flow of dislocation glide and twinning even at elevated temperatures.

High strain rate deformation behavior of a continuous fiber reinforced aluminum metal matrix composite

An aluminum metal matrix composite reinforced with continuous unidirectional α-Al 2O 3 fibers has been compression tested at quasi-static and dynamic strain rates. In the transverse direction, the composite showed increased flow stress and maximum stress within the studied strain rate regime, 10 −3 to 3500 s −1. The strain rate sensitivity of the flow stress in this direction was found to be similar to that of a similar, but unreinforced, alloy determined from previous work. In the longitudinal direction, the maximum stress of the composite increased with increasing strain rate within the range 10 −5 to 700 s −1. The strain rate dependent maximum stress in this direction was described by the strain rate dependent fiber buckling stress.

High strain rate deformation of martensitic NiTi shape memory alloy

Shape memory alloys possess three fundamental properties due to their unique deformation mechanisms: shape memory effect, superelasticity and high damping capacity. The first two properties have already shown significant prospects for application, while the third one has not attracted significant attention. Recently, however, these materials appear promising for civil engineering applications due to the high damping capacity, coupling with good strength, ductility and very good corrosion resistance. Previous research on the deformation behavior of SMAs has been focused on low strain rates. Recently, some preliminary results have been reported on stress-induced martensite formation with austenitic SMAs subjected to impact. However, the high strain rate deformation behavior of SMAs in their martensitic state has not been reported. In the present work, the mechanical behavior of a martensitic NiTi SMA under very high state rate (3 {times} 10{sup 3} s{sup {minus}1}) compression is obtained and is primarily compared to its low rate (3 {times} 10{sup {minus}4} s{sup {minus}1}) deformation behavior.

A finite deformation continuum\\discrete model for the description of fragmentation and damage in brittle materials

A dynamic finite element analysis of large displacements, high strain rate deformation behavior of brittle materials is presented in total Lagrangian coordinates. A continuum\\discrete damage model capable of capturing fragmentation at two size scales is derived by combining a continuum damage model and a discrete damage model for brittle failure. It is assumed that size and distribution of potential fragments are known a priori, through either experimental findings or materials properties, and that macrocracks can nucleate and propagate along the boundaries of these potential fragments. The finite deformation continuum multiple-plane microcracking damage model accounts for microcracks within fragments. Interface elements, with cohesive strength and reversible unloading before debonding, between potential fragments describe the initiation of macrocracks, their propagation, and coalescence leading to the formation of discrete fragments. A surface-defined multibody contact algorithm with velocity dependent friction is used to describe the interaction between fragments and large relative sliding between them. The finite element equations of motion are integrated explicitly using a variable time step. Outputs are taken at discrete time intervals to study material failure in detail. The continuum\\discrete damage model and the discrete fragmentation model, employing interface elements alone, are used to simulate a ceramic rod on rod impact. Stress wave attenuation, fragmentation pattern, and overall failure behavior, obtained from the analyses using the two models, are compared with the experimental results and photographs of the failing rod. The results show that the continuum\\discrete model captures the stress attenuation and rod pulverization in agreement with the experimental observations while the pure discrete model underpredicts stress attenuation when the same potential fragment size is utilized. Further analyses are carried out to study the effect of potential fragment size and friction between sliding fragments. It is found that compared with the continuum\\discrete damage model, the discrete fragmentation model is more sensitive to the multi-body discretization.

Adaptive FEM computation of geometric and material nonlinearities with application to brittle failure

A model is presented for the dynamic finite element analysis of large-strain, high strain rate deformation behavior of materials. A total Lagrangian formulation is used in the derivation of discrete equations of motion. Both an isochoric finite deformation plasticity model, including rate and temperature effects, for metals, and a multiple-plane microcracking model for ceramics are introduced. In addition, algorithms are presented for correcting finite element mesh distortion through mesh rezoning, optimization, and refinement. A surface-defined multibody contact algorithm designed to handle large relative displacements between bodies, with addition for friction, is included. Extensions of the mechanical contact to account for heat fluxes between sliding bodies and the treatment of body interfaces with cohesive strength are presented within a unified framework. Two test examples are examined, simulating a modified Taylor rod impact experiment, in which an aluminum anvil strikes a confined or unconfined ceramic rod. Axial and radial velocities are computed at the free end of the ceramic and at 30 mm from the impact surface, respectively. Comparisons with experimental traces reveal that the simulations produce the same overall features observed in the experimental data.

High strain rate behavior of a SiC particulate reinforced Al 2O 3 ceramic matrix composite

The high strain rate deformation behavior of composite materials is important for several reasons. First, knowledge of the mechanical properties of composites at high strain rates is needed for designing with these materials in applications where sudden changes in loading rates are likely to occur. Second, knowledge of both the dynamic and quasi-static mechanical responses can be used to establish the constitutive equations which are necessary to increase the confidence limits of these materials, particularly if they are to be used in critical structural applications. Moreover, dynamic studies and the knowledge gained form them are essential for the further development of new material systems for impact applications. In this study, the high strain rate compressive deformation behavior of a ceramic matrix composite (CMC) consisting of SiC particles and an Al{sub 2}O{sub 3} matrix was studied and compared with its quasi-static behavior. Microscopic observations were conducted to investigate the deformation and fracture mechanism of the composite.