The American Society for Testing and Materials (ASTM) is an independent organization devoted to the development of standards.

American Society for Testing and Materials

Biocomposites reinforced with natural fibers: 2000–2010

Double-network (DN) gels have drawn much attention as an innovative material having both high water content (ca. 90 wt%) and high mechanical strength and toughness. DN gels are characterized by a special network structure consisting of two types of polymer components with opposite physical natures: the minor component is abundantly cross-linked polyelectrolytes (rigid skeleton) and the major component comprises of poorly cross-linked neutral polymers (ductile substance). The former and the latter components are referred to as the first network and the second network, respectively, since the synthesis should be done in this order to realize high mechanical strength. For DN gels synthesized under suitable conditions (choice of polymers, feed compositions, atmosphere for reaction, etc.), they possess hardness (elastic modulus of 0.1–1.0 MPa), strength (failure tensile nominal stress 1–10 MPa, strain 1000–2000%; failure compressive nominal stress 20–60 MPa, strain 90–95%), and toughness (tearing fracture energy of 100∼1000 J m−2). These excellent mechanical performances are comparable to that of rubbers and soft load-bearing bio-tissues. The mechanical behaviors of DN gels are inconsistent with general mechanisms that enhance the toughness of soft polymeric materials. Thus, DN gels present an interesting and challenging problem in polymer mechanics. Extensive experimental and theoretical studies have shown that the toughening of DN gel is based on a local yielding mechanism, which has some common features with other brittle and ductile nano-composite materials, such as bones and dentins.

Why are double network hydrogels so tough

: An overview of the virtual crack closure technique is presented. The approach used is discussed, the history summarized, and insight into its applications provided. Equations for two-dimensional quadrilateral elements with linear and quadratic shape functions are given. Formula for applying the technique in conjuction with three-dimensional solid elements as well as plate/shell elements are also provided. Necessary modifications for the use of the method with geometrically nonlinear finite element analysis and corrections required for elements at the crack tip with different lengths and widths are discussed. The problems associated with cracks or delaminations propagating between different materials are mentioned briefly, as well as a strategy to minimize these problems. Due to an increased interest in using a fracture mechanics based approach to assess the damage tolerance of composite structures in the design phase and during certification, the engineering problems selected as examples and given as references focus on the application of the technique to components made of composite materials.

/pdf/virtual-crack-closure-technique-history-approach-and-53akn4ewzt.pdf

Virtual crack closure technique: History, approach, and applications

An engineering solution for mesh size effects in the simulation of delamination using cohesive zone models

https://research-information.bris.ac.uk/ws/files/241900439/In_situ_CT_paper_authors_version.pdf

In situ Characterization of Trans-laminar Fracture Toughness using X-ray Computed Tomography

This effect has been analyzed using Rosen's model with experimental data for the nonlinear stress-strain response of the epoxy resin. Finite element analysis has been carried out on two standard indirect compression specimens, including the effect of nonlinear shear behavior of the composite

Effect of shear stresses in indirect compression tests of unidirectional carbon fiber/epoxy

Delamination due to interaction between overall interlaminar shear and stresses at terminating plies

/pdf/specimens-with-cut-central-plies-an-experimental-and-393o8vo940.pdf

Specimens with Cut Central Plies An Experimental and Analytical Study of Delamination of Unidirectional

We report on the finite element analysis of stress distribution at the coalescence boundary in epitaxial lateral overgrown (ELO) GaN related to voids. Different void geometries were considered in our model to investigate the influence of their size/shape on the stress distribution. Large compressive stress is localized in the vicinity of the voids, also an increased tensile stress is present at the corners of the SiN mask. Confocal micro-Raman mapping experiments confirm the presence of increased stress at the coalescence boundary of ELO GaN.

Michael R Wisnom

Papers

In situ Characterization of Trans-laminar Fracture Toughness using X-ray Computed Tomography

Effect of shear stresses in indirect compression tests of unidirectional carbon fiber/epoxy

Delamination due to interaction between overall interlaminar shear and stresses at terminating plies

Specimens with Cut Central Plies An Experimental and Analytical Study of Delamination of Unidirectional

Finite element analysis of epitaxial lateral overgrown GaN: Voids at the coalescence boundary