Modal Analysis of a Servo-Hydraulic High Speed Machine and its Application to Dynamic Tensile Testing at an Intermediate Strain Rate

Abstract

This paper describes the experimental procedure to identify the predominant frequencies of the high speed testing machine by conducting modal analysis. The effects due to the predominant frequencies of the system and loading rate on the magnitude of system ringing and the flow stress were analyzed by using a single degree-offreedom (SDOF) spring-mass-damper model. The system was then used to study the dynamic tensile behavior of two engineering materials, i.e., polyethylene (PE) fabric-cement composite and Alkaline Resistant (AR) glass fabrics at an intermediate strain rate. The stress oscillations in the response of these materials due to system ringing were addressed. The failure behavior of each material was studied by examining high speed digital camera images of specimens during the test. The validity of the dynamic tensile tests was investigated by examining the condition of dynamic stress equilibrium-a criterion used in split Hopkinson pressure bar (SHPB) tests. The results show that the quantitative criterion for a valid SHPB test is also applicable to dynamic tensile tests of these materials at the intermediate strain rate.

Flow Stress Measurement and Dynamic Response Analysis of Hot Compression Test Machine at High Strain Rates

“…Accordingly, the ram is programmed to be accelerated in the run-up. Solving the above equation, we obtain the following formulation: 11,19)…”

“…They used a linear regression method to evaluate the natural frequency of a compression test machine. Zhu et al 11) used an autoregressive method to fit the data and proposed spring-mass-damper model with a single degree of freedom to explain the elastic phenomenon.…”

Finite Element Modeling of Ballistic Impact on Kevlar 49 Fabrics

“…E 33 is taken as zero simply because shell elements are used to model the fabric. The values for E 11 , E 22 , G 12 , G 31 , and G 23 are a function of several factors including current stress and strain, stress and strain history, and strain rate. The determination of these material properties will be discussed in the following section.…”

“…Yarn strength decreases slightly as the gage length increases; whereas the failure strain of the Kevlar ® 49 yarns was independent of the gage length, however decreased slightly as the strain rate increased. Zhu et al [8][9][10][11] conducted dynamic tensile testing on Kevlar ® 49 single yarn and fabrics using a servo-hydraulic high speed machine [12][13][14][15][16][17][18] and found that the Young's modulus, tensile strength, maximum strain and toughness increased with increasing strain rate over a range of 20 to 170 s -1 .…”

Quasistatic Strain Rates’ Effect to the Properties of Advanced Steels for Automotive Industry

“…Thus, material properties not only for static, but also dynamic strain rates have to be known for complex analysis of car-body deformation components. The strain rate raising, resistance to deformation increases as well and some materials have shown material micro-and sub-structure change [1,2], yield strength and deformation to fracture growth [3].…”