Fracture mechanics test data

Fracture mechanics test data for selected FRP composites... 

Data obtained from fracture mechanics tests provide useful information concerning the ability of different materials, or of different variants of the same material, to resist crack propagation and concerning the possible influence of existing cracks. 

The second example demonstrates how data from a standard fracture mechanics test might be used to predict failure for other... 

This chapter will first discuss fracture mechanics applications to polymer composites in aerospace, and then compile the different test methods by type of load. The industiy-specific fracture mechanics test procedures for FRP composites, such as the Airbus Industries Test Method (AITM) or Boeing Support Specification (BSS), are essentially based on test procedures developed by national or international standardization agencies. This will be followed by a section with literature data to highlight selected effects of processing and material layup and type. Further sections will discuss non-unidirectional reinforcement and testing under environmental conditions that are relevant to aerospace applications, and the chapter concludes with an outlook on materials and test development trends. 

The literature published on fracture mechanics testing of FRPs in the last 40 years comprises a large database on delamination resistance or fracture toughness of different types of FRPs. An early review [51] compiled the data available at that time. Selected data from quasi-static mode I and mode II tests on FRPs were compared by O Brien [52], and quasi-static mode I test data from carbon—fibre epoxy and poly-ether-ether-ketone (PEEK) by Brunner [53]. Mechanical properties of FRP composites are compiled in the Composite Materials Handbook version F (2002) [9—11], but this does not comprise fracture mechanics data. Hence, there is no comprehensive and up-to-date database on the available data or literature. 

Not only the specimen thickness is of importance, but also the ratio of the initial notch size a and the specimen width W. In Figure 5.6, crack resistance curves from quasi-static fracture mechanics tests (SSM) are shown. The materials were SBR vulcanizates without (a, c) and with carbon black N330 (b, d). The mixtures of the non-reinforced materials contained different amounts of sulphur so that a different crosslink density could be obtained. For both, the unfilled and the CB filled vulcanizates, the comparison of the crack resistance curves indicates an influence of the a/W ratio. The analysis of the data [05Rei] led to the conclusion that 0.2 is a suitable a/W ratio for such experimental investigations. 

Fracture mechanics tests were carried out on ABS pofymer, using 6 side-grooved compact tension specimens with IF 50 mm, ag-25 mm, B = 15 mm. The side grooves were 1.5 mm deep, with an included angle of 45° and a root radius of 0.25 mm. Measured values of Aa were 0.1,03,0.5, 0.7, and 0.9 mm. The corresponding work iiq>uts were 0.41,0.66, OBI, 0.92, and 1.02 J. Calculate (or each valid data point, and hence obtain a value for 0.2-Solution... 

ASME (1999a), ASME Boiler and Pressure Vessel Code Case N-629, Use of fracture toughness test data to establish reference temperature for pressure retaining materials, Section XI, Division i, American Society of Mechanical Engineers, New York. 

Another basic major advantage is that the cyclic-fatigue fracture-mechanics data may be gathered in a relatively short time-period, but may be applied to other designs of bonded joints and components, whose lifetime may then be predicted over a far longer time-span. Obviously, the fracture-mechanics tests need to be conducted under similar test conditions and environments as the joints, or components, whose service-life is to be predicted. This is important since the fracture-mechanics test specimens do need to exhibit a similar mechanism and locus of failure (e.g. cohesively through the adhesive layer, or interfacially between the adhesive and substrate, or through the oxide layer on the metallic substrate, etc.) as observed in the joints, or components, whose lifetime is to be ranked and predicted. 

El 94-98(2010)e1 Standard Guide for Evaluating Data Acquisition Systems Used in Cyclic Fatigue and Fracture Mechanics Testing... 

A scheme i ch seeks to rectify this situation is the application of fracture mechanics and this is now quite wdl developed [e.g. 1], The data whidi are so produced are intrinsic material propoties and, as such, are usefid bodi for proper material qualification and fffl- use in engineering design. However, fracture mechanics testing methods are not simple to perform. 

Mechanical Properties. Mechanical properties obtained on the cured resins included tensile strength and fracture toughness. Tensile tests were run on an Instron model 1122 Universal Tester with a crosshead speed of 0.02 /minute. Tests were run on dry and saturated samples in air. Fracture toughness (K ) values have been obtained using a MTS 610 Materials Testing System at 0.02 /minute at ambient and elevated temperatures in air. The compact tensile specimens tested were 0.5 x 0.5 x 0.125 in dimension. Mechanical properties data are based on the results from four or more tests run at each condition. 

Eisele et al24 describe the so called tear analyzer using a strip test piece with a cut in one edge cycled in tension, which can be considered the classic geometry for obtaining fracture mechanics data on rubbers. This sophisticated instrument introduces nothing new in concept but has a temperature controlled chamber and can operate at different frequencies, pre-strains and strain amplitudes, with automatic compensation for set. 

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