Search Results for strain energy release rate

Delamination is one of the most commonly observed failure modes in composite materials. This article describes the three fundamental fracture failure modes of composite delamination, namely, opening, in-plane shearing, and tearing or scissoring shearing modes. It discusses the characterization and analysis of delamination. The article also reviews the prediction of delamination factors, such as flexbeam fatigue life, and skin/stiffener pull-off strength and life.

This article addresses the issue of the implementation of composite damage tolerance requirements as it relates to military aircraft. It presents a brief introduction on the durability impact threat, damage tolerance impact threat, and other damage tolerance damage threats. The article summarizes damage tolerance criteria and durability criteria for military aircraft. It discusses the damage tolerance design philosophy for metallic structures and composite structures of the aircraft. The article describes the implementation of a damage tolerance analysis methodology in terms of the mechanics based model, the regression algorithm, and the semi-empirical analysis.

There are many different types of polymeric materials, ranging from glassy to semicrystalline polymers and even blends. Their mechanical properties range from pure elastic with very high strains to fracture (elastomers) to almost pure linear elastic (Hookian behavior) with low strains to fracture (glassy polymers). This article provides an overview of historical development of fracture behavior in polymers. It discusses the processes involved in three fracture test methods for polymers, namely linear elastic fracture mechanics, elastic-plastic fracture mechanics, and post-yield fracture mechanics.

The properties of unidirectional composite (UDC) materials are quite different from those of conventional, metallic materials. This article provides information on the treatment of UDC stress-strain relations in the forms appropriate for analysis of thin plies of material. It explains the development of the relations between mid-surface strains and curvatures and membrane stress and moment resultants. The article discusses the properties, such as thermal expansion, moisture expansion, and conductivity, of symmetric laminates and unsymmetric laminates. It describes the distribution of temperature and moisture through the thickness of a laminate. Stresses caused due to mechanical loads, temperature, and moisture on the laminate are analyzed. The article concludes with information on interlaminar cracking, free-edge delamination, and transverse cracks of laminates.

This article discusses the J-integral-based single and multiple specimen techniques of the ASTM E 1737 test method for determining plane strain fracture toughness of polymeric materials. It describes the fracture toughness testing of thin sheets and films. The article concludes with information on the alternative methods for determining the fracture toughness of polymer materials.

Fracture mechanics is a multidisciplinary engineering topic that has foundations in both mechanics and materials science. This article summarizes the microstructural aspect of fracture resistance in structural materials. It provides a discussion on basic fracture principles and schematically illustrates the mechanism of crack propagation. The article describes the fracture resistance of high-strength steels, aluminum alloys, titanium alloys, and composites such as brittle matrix-ductile phase composites and metal-matrix composites. It also lists the effects of microstructural variables on fracture toughness of steels, aluminum alloys, and titanium alloys.

Detailed analyses and test correlations are typically required to support design development, structural sizing, and certification. This article addresses issues concerning building block levels ranging from design-allowables coupons up through subcomponents, as these levels exhibit a wide variety of test-analysis correlation objectives. At these levels, enhanced analysis capability can be used most effectively in minimizing test complexity and cost while also reducing design weight and risk. The article discusses the examples of tests for which good correlative capability has shown significant benefit. These include notched (open and/or filled hole) tension and compression, inter/intralaminar shear and tension, and pin bearing.

The fracture-mechanics technology has significantly improved the ability to design safe and reliable structures and identify and quantify the primary parameters that affect structural integrity of materials. This article provides a discussion on fracture toughness of notched materials by explaining the ductile-to-brittle fracture transition and by correlating KId, KIc, and Charpy V-notch impact energy absorptions. It highlights the effects of constraint, temperature, and loading rate on the fracture transition. The article discusses the applications of fracture mechanism in limiting of operating stresses. It describes the mechanisms, testing methods, and effecting parameters of two main categories of fracture mechanics: linear-elastic fracture mechanics and elastic-plastic fracture mechanics. The article concludes with a discussion on the three major progressive stages of fatigue: crack initiation, crack growth, and fracture on the final cycle.

This article begins with a review of the purposes of mechanical characterization tests and the general considerations related to the mechanical properties of anisotropic systems, specimen fabrication, equipment and fixturing, environmental conditioning, and analysis of test results. It provides information on the specimen preparation, instrumentation, and procedures for various mechanical test methods of fiber-reinforced composites. These include the compression test, flexure test, shear test, open hole tension test, and compression after impact test. The article describes three distinct fracture modes, namely, crack opening mode, shearing mode, and tearing mode. It presents an overview of fatigue testing and fatigue damage mechanisms of composite materials and reviews the types of mechanical measurements that can be made during the course of testing to assess fatigue damage. The article concludes with a discussion on the split-Hopkinson pressure bar test.