Studying the deformation and fracture properties of soft materials can not only provide insight into the physical mechanisms underlying their superior properties and functions but also benefit the design and fabrication of rubberlike materials. In this paper, an application of the experimental digital moire method to determine the damage zone around crack tip for rubberlike material is presented. The measurement principles and the basic procedures of the method are explained in detail. The in-plane defomation distributions of crack tip fields under Mode I fracture condition are measured. In addition, the deformation of crack tip fields in the damage zones is also analyzed using the sector division mode. Finally, an analysis of the damage zone is proposed to describe crack-tip fields in rubber-like materials with large deformation.

Pressure piping is the most productive way for large-volume compressed natural gas (CNG) transportation. In pipeline constructions, the thickness at the point where two pipes join together is often not consistent due to the mismatch in dimensions, and thus stress concentrations can often occur at the pipe joints, causing safety concerns. Therefore, it is important to accurately analyze the key influencing factors of dimensional mismatch defects, providing a theoretical basis for the preliminary design and post-repair of pipelines. This work uses the smoothed finite element method (S-FEM) that has been proven accurate in stress analysis compared with the traditional FEM. Since geometry and load of the pressure piping are axisymmetric, a novel axisymmetric S-FEM element is first developed, coded and integrated in ABAQUS using the User-defined Element Library (UEL). Intensive studies are then carried out to examine the effects of different levels of mismatch in the thicknesses of two joined pipes and the effects of the radius of the transitional fillet used to bridge the mismatches. It is found that the maximum hoop stress reduces as the radius of the transitional fillet increases. For the thinner section of the pipe, the maximum hoop stress is only affected by the thickness mismatch.

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A new constitutive model which is modified from Gao’s constitutive model has been introduced to analyze the finite deformation of a circular membrane with an embedded rigid inclusion under uniform pressure. Based on the basic controlling equations, the constitutive parameters and the dimension of the rigid inclusion have been discussed to demonstrate the influences on the membrane stresses.

Following the modified Gurson model in meso-mechanics, the models with spherical holes are established by the assumption which the matrix meets the two-parameter elliptic yield condition. The macroscopic stress expression which contains micro structure parameters and the material equation of yield surface are given by the upper bound theorem of plastic limit analysis. The parameters of the matrix material and damage(porosity) which impact on macroscopic yield surface equation are discussed. These works provide theory foundations for material damage and design.