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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.

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Virtual crack closure technique: History, approach, and applications

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

Prediction of Delamination Growth at Discontinuous Plies due to Cyclic Loading

The failure mechanisms controlling notched static tensile and compressive response of composites are described. The effect of notch size on strength for both sharp and blunt notches is considered along with the key factors affecting the behavior. Methods for predicting strength are presented, with a brief discussion on the potential to mitigate notch sensitivity.

8.6 Notch Sensitivity of Composites

This paper reviews recent published research on failure of fibre reinforced composite materials and structures in the UK. A number of themes are covered: Microstructural Effects, Transverse Cracking, Enhanced Interlaminar Properties, Cohesive Zone Modelling, Compression, Impact, High Strain Rate Behaviour, Fatigue, Failure Criteria and Prediction, Scaling Effects and Multiscale Modelling, Damage Detection, 3-D Woven Composites and Civil Engineering Composites.

Composite Materials and Structures Failure Research in the UK

The Relationship Between Size Effect and Strength Variability in Unidirectional Carbon Fibre-Epoxy

Longitudinal tensile tests have been conducted on unidirectional SiC fibre reinforced 6061 aluminium matrix composites in the annealed and as-manufactured conditions. The results are presen...

Michael R Wisnom

Papers

Prediction of Delamination Growth at Discontinuous Plies due to Cyclic Loading

8.6 Notch Sensitivity of Composites

Composite Materials and Structures Failure Research in the UK

The Relationship Between Size Effect and Strength Variability in Unidirectional Carbon Fibre-Epoxy

Non-linear stress-strain behaviour of unidirectional silicon carbide fibre reinforced aluminium alloy