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Applied Composite Materials: An International Journal for the Science and Application of Composite Materials (v.14, #1)
Determination of Compressive Properties of Fibre Composites in the In-plane Direction According to ISO 14126. Part 1: A Round Robin Test by Konrad Schneider (pp. 1-15).
Over the years different tests are established to characterise the compressive properties of composites in the in-plane direction. The international standard ISO 14126 (2000) (Fibre-reinforced plastic composites — determination of compressive properties in the in-plane direction, ISO 14126: 1999 (E), Faserverstärkte Kunststoffe, Bestimmung der Druckeigenschaften in der Laminatebene, DIN EN ISO 14126: 2000-12) tries to standardise these tests. The described wide range of arrangements enables to continue with the present practice to a large extent. But the standard doesn’t say anything about the precision of the method. Four labs performed a round robin test to check the precision and reproducibility of the Celanese-type arrangement for different composite materials, structures and dimensions. The test procedure is critically discussed and some proposals for the applicability of the method are derived. Mainly the advantages of optical monitoring the overall as well as the local strain of the specimen are demonstrated for the characterisation the failure process. By this method some of the reasons of unsatisfying reproducibility can be cleared up.
Keywords: compressive test; Celanese; composite testing
Experimental Study on Tensile Behavior of Carbon Fiber and Carbon Fiber Reinforced Aluminum at Different Strain Rate by Yuanxin Zhou; Ying Wang; Shaik Jeelani; Yuanming Xia (pp. 17-31).
In this study, dynamic and quasi-static tensile behaviors of carbon fiber and unidirectional carbon fiber reinforced aluminum composite have been investigated. The complete stress–strain curves of fiber bundles and the composite at different strain rates were obtained. The experimental results show that carbon fiber is a strain rate insensitive material, but the tensile strength and critical strain of the Cf/Al composite increased with increasing of strain rate because of the strain rate strengthening effect of aluminum matrix. Based on experimental results, a fiber bundles model has been combined with Weibull strength distribution function to establish a one-dimensional damage constitutive equation for the Cf/Al composite.
Keywords: carbon fiber; metal matrix composite; tensile properties
Essential and Non-essential Work of Fracture of PI/SiO2 Hybrid Thin Films by Z. D. Wang; J. J. Lu (pp. 33-45).
Essential work of fracture (EWF) analysis is used to study the effect of the silica doping level on fracture toughness of polyimide/silica (PI/SiO2) hybrid films. By using double-edge-notched-tension (DENT) specimens with different ligament lengths, it seems that the introduction of silica additive can improve the specific essential work of fracture (w e ) of PI thin films, but the specific non-essential work of fracture (βw p ) will decease significantly as the silica doping level increasing from 1 to 5 wt.%, and even lower than that of neat PI. The failure process of the fracture is investigated with online scanning electron microscope (SEM) observation and the parameters of non-essential work of fracture, β and w p , are calculated based on finite element (FE) method.
Keywords: thin film; fracture; plane-stress condition; EWF; SEM; FE method
Experimental and Numerical Investigations on the Ballistic Performance of Polymer Matrix Composites Used in Armor Design by M. Colakoglu; O. Soykasap; T. Özek (pp. 47-58).
Ballistic properties of two different polymer matrix composites used for military and non-military purposes are investigated in this study. Backside deformation and penetration speed are determined experimentally and numerically for Kevlar 29/Polivnyl Butyral and Polyethylene fiber composites because designing armors for only penetration is not enough for protection. After experimental ballistic tests, a model is constructed using finite element program, Abaqus. The backside deformation and penetration speed are determined numerically. It is found that the experimental and numeric results are in agreement and Polyethylene fiber composite has much better ballistic limit, the backside deformation, and penetration speed than those of Kevlar 29/Polivnyl Butyral composite if areal densities are considered.
Keywords: ballistic performance; Kevlar; polyethylene; polymer matrix composites; finite element
The Effect of Crack Spacing Distribution on Stiffness Reduction of Cross-ply Laminates by O. Rubenis; E. Spārniņš; J. Andersons; R. Joffe (pp. 59-66).
The effect of transverse crack distribution on the effective mechanical properties of cross-ply laminates is considered. Young’s modulus and Poisson’s ratio dependence on the transverse ply crack density is obtained experimentally for glass fiber/epoxy laminates of lay-ups [02/902]s, [0/902]s, and [0/904]s subjected to uniaxial tensile loading. Crack spacing distributions at the edge of the specimen are also measured at a predefined applied strain. Mechanical property reduction is evaluated for two crack spacing distributions: uniform spacing routinely considered in theoretical derivations and the experimental crack spacing distribution; the results are compared with test data.
Keywords: laminates; transverse cracking; non-uniform crack spacing; elastic properties
Damage Resistance of Composites Based on Glass Fibre Reinforced Low Styrene Emission Resins for Marine Applications by Y. Perrot; C. Baley; Y. Grohens; P. Davies (pp. 67-87).
Composites based on glass fiber reinforced low styrene emission polyester resins have been widely used over the last 10 years, in order to meet increasingly strict safety regulations, particularly in the pleasure boat industry. Previous studies of their mechanical properties suggested that although these resins are generally more brittle than traditional orthophthalic polyester resins this did not adversely affect the properties commonly used for quality control (short beam shear and tensile failure strength of mat reinforced composites). In the present paper results from a more detailed study of damage behaviour are presented. Tests include fracture toughness (K Ic ) tests on resins, fibre/matrix interface energy, detection of composite damage initiation in tension by acoustic emission, composite delamnation (G Ic and G IIc ), and low energy impact. Overall the results indicate that the low failure strain of low styrene emission resins results in significantly lower composite damage resistance.
Keywords: glass fibers; unsaturated polyester; styrene emission; damage initiation; interface properties