Dynamic tensile characteristics of TRIP-type and DP-type steel sheets for an auto-body

Experimental investigation of low-velocity impact characteristics of sandwich composites

This paper presents stress-strain curves of steel sheets for an auto-body obtained at intermediate strain rates with a servo-hydraulic type high speed tensile testing machine. The apparatus has the maximum stroke velocity of 7.8 m/sec to obtain the tensile material properties at a strain rate of up to 500/sec. A special jig fixture is specially designed for accurate acquisition of tensile loads with reduction of the load-ringing phenomenon induced by unstable stress wave propagation at high strain rates. Tensile testing of steel sheets for an auto-body was carried out to obtain stress-strain curves of mild steel and advanced high strength steels at strain rates ranged from 1/sec to 200/sec. The test results provide interesting information regarding the stress-strain curves at intermediate strain rates ranged from 1/sec to 200/sec and demonstrate that strain rate hardening is strongly coupled with strain hardening.

High speed tensile test of steel sheets for the stress-strain curve at the intermediate strain rate

This paper describes an investigation of single-degree-of-freedom models for large mass impact on composite sandwich laminates. The stiffness parameters of the models are derived from the results of three-dimensional quasi-static contact analyses of a rigid sphere indenting a multi-layer sandwich laminate. Energy dissipating elements are incorporated into the models to account for material damage. The validity of the models is examined through comparisons with experimental force history results of impact on six different core and face sheet configurations. It is found that a Maxwell element with the nonlinear spring in series with a viscous damper element best models the impact phenomenon for this boundary condition controlled impact. The damping parameters for each type of laminate analyzed, although initially determined empirically, are found to have a unique relationship to the energy dissipated at the time of maximum contact force. With this relationship known, the damping parameter can be determined a priori to accurately predict the peak contact force and contact duration for these foam and honeycomb sandwich panels.

An investigation of SDOF models for large mass impact on sandwich composites

Tension/compression hardening behaviors of auto-body steel sheets at intermediate strain rates

A dropped-weight test apparatus has been developed that can be used to perform low-speed impact tests on composite aircraft structures. This vertical drop-weight test apparatus is simple, compact, inexpensive and has precision impact and self-arresting design features similar to the more sophisticated, expensive test machines. The test apparatus has been used to perform low-speed impact response studies on laminated composite plates to understand the influence of impactor and target parameters on structural response and to develop a validated analysis method. Some of the experimental results generated by using this test apparatus for composite laminated plates are presented in the present paper and compared with the corresponding analytical results.

C. B. Prasad

Papers

A dropped-weight apparatus for low-speed impact testing of composite structures