This paper discusses the effect of intensity pattern noise on the displacement measurement precision of digital image correlation (DIC). Through mathematical deduction, a formula is presented to estimate the displacement measurement error caused by intensity pattern noise. The resulting formula synthetically reflects the effects of the variance of noise, the intensity variance and the subset size on the displacement measurement precision. To verify the correctness of the resulting formula, two experiments are done. The first one is a real self-correlation experiment, and aims to analyze the effect of the subset size, while the second is a numerical self-correlation experiment, and is to analyze to the effect of the different noise levels. The experimental results are in good agreement with the theoretical predictions.

Using finite element program generator (FEPG) of Beijing Feijian Software Corporation, a relative finite element procedure is developed for the three-dimensional viscoplasticity model which can characterize well the nonlinear behavior and strain-rate dependence behavior of thermoplastic composite, AS4-PEEK. Interlaminar stresses of angle-ply laminates []s for different strain rates under uniaxial tension are calculated. The effects of the variation of strain rates on interlaminar stresses in the vicinity of free edges of AS4-PEEK composite laminates are investigated. From the three-dimensional plots of the interlaminar stresses, it can be seen that distant free-edge effects and end-edge effects exist in the angle-ply laminates []s. The interlaminar stresses in free-edges and two ends increase with increasing strain rates. The extents to which the strain rates affect interlaminar stresses are depicted.

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Three-dimensional finite element interlaminar stress solutions of composite laminates with resin layers under uniform axial strain are presented. Their three-dimensional distributions are plotted. In the cross-ply laminate, interlaminar normal and shear stresses are shown to be of free-edge effect. But shear stresses are found to be significantly reduced in the free-edge region, which show some conformity to the boundary stress conditions. In the angle-ply laminate, the stress distributions all vary significantly along both extension and width directions. There exists free-edge effects and end-edge effects in this case; however, the peaky interlaminar stresses are not exactly at the edges, but are near the edge regions.

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