The Effect of Test System Misalignment in the Dynamic Tension Test

Abstract

An analysis of test system misalignment is presented for dynamic tension test. Sheet type rectangular 1100-0 aluminum specimens are used for discussion.For a constant strain rate tension test, the strain rate is constant only on the neutral axis of the specimen. The following resultF have been obtained: (a) The lower the strain rate is,the more significant the misalignment errors become. (b) Misalignment errors of 50% have been found at the extreme fibers of the specimen. (c) The strain rate variation in the cross-section decreases with increasing plastic strain and vanishes at plastic strain equal to 0.8% at the midspan of the spec-mien.. (d) The neutral axis will shift toward the centerline of the specimen as the plastic strain increases. But, it will reach a limit and will not completely move back to the centerline.A more restricted uniform strain rate formulation is also presented.The result is compared with that of the nonuniform strain rate formulation. In [3], a comprehensive analysis of misalignment effect was presented for tension test under static loading condition. In the analysis, three cases of misalignment were considered, which were the symmetric case, the cantilever case, and the case of the pinned specimen with eccentricity. It was found that the symmetric case is the most critical one as far as the effect of misalignment is concerned. In addition, Wu and Rummler concluded that the stressstrain curve is significantly affected by misalignment at strain levels corresponding to the knee portion of the stress-strain curve. Moreover, the strain at the outermost fivers of the specimen is strongly affected by misalignment and the misalignment effects are smaller for load trains with longer pull rods.The dynamic mechanical properties of materials have become increasingly important in the recent years. Tension tests have been conducted at various fixed strain rates to determine the dynamic behavior of materials. The problem h of test system alignment which exists in the static test would also carry over to the dynamic test. However, to the present investigators' knowledge, the alignment problem under dynamic tensile load has not been investigated in the literature. I41J A

Analysis of Test System Misalignment in the Creep Test

“…The essential features of the symmetric case of misalignment is also presented in Fig. 2b, The dlscretized numerical model is identical to that of Ref, [7] and is reproduced in Fig. 3.…”

“…The implication is that greater bending moment is obtained for the extreme fibers at the pre-loadlng stage reported in Ref. [7]. A conclusion of Ref.…”

“…A conclusion of Ref. [7] is that the error range for the extreme fibers is always decreasing with the increasing 8o" Figure 5 also indicates that this error range in stress for a fixed 8 decreases with the creep time. • Perhaps the most significant of all the results of this paper is tha_ presented in Fig.…”