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Applied Composite Materials: An International Journal for the Science and Application of Composite Materials (v.14, #3)
Evaluation of Stiffness Terms for Z-cored Sandwich Panels by D. Zangani; M. Robinson; A. G. Gibson (pp. 159-175).
This paper presents a model for the stiffness terms of composite sandwich panels with structured cores (referred to as ‘z-core’ panels). Truss-cores, corrugated-cores and double-corrugated cores containing a polymeric foam were considered. The model was validated, both through finite element simulation and through comparison with the results of experimental three point bend tests on panels. A parametric study was performed to assess the performance of the different reinforced panel configurations.
Keywords: Sandwich composites; Structured core; Modelling; Finite element analysis
Determination of Compressive Properties of Fibre-Reinforced Polymers in the In-Plane Direction According to ISO 14126. Part 2: A Critical Investigation of Failure Behaviour by K. Schneider; B. Lauke (pp. 177-191).
In Part 1 of this paper, we have compared the compression modulus and compressive strength obtained during a round robin test with the so-called Celanese-type equipment in four laboratories. The scatter of the measured values was considerable, with a variation coefficient of about 10% for the modulus and about 15% for the compressive strength. The main source responsible for this disappointing result is supposed to lie in the stress/strain concentrations induced by the tabs that support the specimen and transfer the load from the machine to the specimen. Detailed optical examinations have shown that cracks are initiated in this region or at least run into it after being initiated away from the tabs. Additionally, the local deformations were determined during testing with a grating technique. The local strains in different directions agree qualitatively with the results of finite-element modelling of the Celanese-type testing. The strain concentrations near the free surface of the tabs, which are responsible for the crack initiation, can be reduced if the tabs do not have a sharp 45° edge but a certain curvature.
Keywords: Compressive test; Compressive failure; Celanese; Composite testing
In-plane Compressive Behaviors of 3-D Textile Composites at Various Strain Rates by Baozhong Sun; Bohong Gu (pp. 193-207).
The in-plane compressive behaviors of 3-D textile composites, which including 3-D woven composite, multi-axial multi-layer warp knitted (MMWK) composite and 3-D braided composite, were studied at quasi-static and high strain rate compression loading. The compression behaviors at high strain rates (600∼2,500/s) were tested with split Hopkinson pressure bar (SHPB). The quasi-static compressive tests were conducted on a MTS 810.23 tester and compared with the results at high strain rates. The comparisons indicate that the compression stiffness, failure stress and failure strain for the three kinds of 3-D textile composites are sensitive to strain rate. The MMWK composite has higher failure stress than the 3-D woven composite and 3-D braided composite at the same strain rate; however, the failure strain of the 3-D braided composites is higher than that of the 3-D woven composite and 3-D knitted composite at quasi-static compression because of the quasi-isotropic structure feature in the 3-D braided composite. The compressive failure modes of the 3-D woven composite, MMWK composite and 3-D braided composite are totally different because of the different preform structure.
Keywords: 3-D woven composite; Multi-axial multi-layer warp knitted (MMWK) composite; 3-D braided composite; Split Hopkinson pressure bar (SHPB); In-plane compression; Strain rate
Influence of Hygrothermal Conditioning on the Elastic Properties of Carall Laminates by E. C. Botelho; R. S. Almeida; L. C. Pardini; M. C. Rezende (pp. 209-222).
The influence of hygrothermal conditioning on mechanical properties of Carall laminates have been investigated by tensile and compression tests. The environmental factors can limit the applications of composites by deteriorating the mechanical properties during service. The importance of temperature at the time of conditioning plays an important role in environmental degradation of such composite materials. In this work, the results show that for carbon fiber/epoxy composites tensile and compression values decrease after hygrothermal conditioning. However, the changes on mechanical properties of Carall are negligible, regardless the hygrothermal conditioning.
Keywords: Carbon fiber/epoxy composites; Hygrothermal effects; Tensile properties
Influence of Surface Modification on Tribo-Performance of Hybrid Glass/PTFE Fabric Composite with Phenolic Resin Binder by Fenghua Su; Zhaozhu Zhang (pp. 223-234).
The fabric/phenolic composites with the pure and silanized hybrid glass/PTFE fabric were prepared by dip-coating of the hybrid glass/PTFE fabrics in a phenolic resin. The friction and wear performances of the resulting fabric composites were evaluated using pin-on-disc wear tester. The composition change of the glass fabric in hybrid glass/PTFE fabric after silanization was analyzed by FTIR spectroscopy. The morphologies of the composite structures and the worn surfaces of the composites were analyzed by means of scanning electron microscopy (SEM). The results show that the fabric/phenolic composite with the β-aminoethyltrimethoxylsilane silanized hybrid glass/PTFE fabric can obtain the highest load-carrying capacity and the best wear-resistance, followed by the composite with γ-glycidoxypropyltrimethoxysilane silanized hybrid glass/PTFE fabric. Chemical reactions have achieved as the hybrid glass/PTFE fabric was silanized with β-aminoethyltrimethoxyl silane or γ-glycidoxypropyltrimethoxy silane, which contribute to strengthen the bonding strength between the fabric and the adhesive and hence to improve the tribological properties of the hybrid glass/PTFE fabric composites.
Keywords: Fabric/phenolic composites; Hybrid glass/PTFE fabric; Phenolic resin; Surface modification; Friction and wear behaviors