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Applied Composite Materials: An International Journal for the Science and Application of Composite Materials (v.9, #3)
Effect of Particulate Silicon Carbide on Cyclic Plastic Strain Response and Fracture Behavior of 6061 Aluminum Alloy Metal Matrix Composites by T. S. Srivatsan; Meslet Al-Hajri; B. Hotton; P. C. Lam (pp. 131-153).
In this paper, the cyclic stress response and cyclic stress–strain response characteristics, cyclic strain resistance and low-cycle fatigue life, and mechanisms governing the deformation and fracture behavior of aluminum alloy 6061 discontinuously reinforced with silicon carbide (SiC) particulates are presented and discussed. Two different volume fractions of the carbide particulate reinforcement phase in the aluminum alloy metal matrix are considered. The composite specimens were cyclically deformed using fully reversed tension–compression loading under total strain-amplitude-control. The stress response characteristic was observed to vary with strain amplitude. The plastic strain-fatigue life response was found to degrade with an increase in carbide particulate content in the metal matrix. The fracture behavior of the composite is discussed in light of the interactive influences of composite microstructural effects, cyclic strain amplitude and concomitant response stress, deformation characteristics of the composite constituents and cyclic ductility.
Keywords: aluminum alloy; metal matrix composite; cyclic fatigue; deformation; fracture; microstructure
Matrix-Dominated Damage in Notched Cross-Ply Composite Laminates: Experimental Observations by C. J. Liu; J. C. Sterk; A. H. J. Nijhof; R. Marissen (pp. 155-168).
The matrix-dominated damage in three highly transparent notched cross-ply laminates with double-edge-semicircular notches were experimentally investigated under a monotonously increasing quasi-static tensile load. A newly designed computer controlled digital camera-video recorder system was successfully used to record the “real time” damage development due to the enhanced stresses around the notches. The damage states were quantitatively characterised as a function of the nominal strain or stress. It was observed that the notches have significant influences on the formation and propagation of the matrix-dominated subcritical damage. The damage states, which depend on the type of the laminate and the size of the notches, appeared to be highly reproducible. Instead of the conventional longitudinal cracks (splits) and the free-edge delamination in unnotched specimens, notch-induced splits (NISs) and notch-induced delamination (NID) were observed. The notches speed up the transverse damage growth in the areas near the notches, both in density and in length. The ultimate strength of the laminates with different notch size is significantly different, due to the diversities of the final failure mechanisms. The notch size and the laminar thickness are two key parameters determining the mode of the matrix damage and the final failure mechanisms of the laminates.
Keywords: cross-ply laminates; notch effects; damage mechanisms; notched strength
Preliminary Investigation of the Wear Behaviour of Self-lubricating Carbon Fibre Reinforced Glass Matrix Composites in Vacuum by G. Gevorkian; H.-J. Schorcht; H. Kern; A. R. Boccaccini (pp. 169-177).
The self-lubricating wear behaviour of a C-fibre reinforced borosilicate glass matrix composite was investigated using a vane-stator configuration resembling a rotating vacuum pump. The vanes were made of the composite material and the stator was of cast iron. Tests were carried out under varying loads in the range 3.8 to 5.8 N. Rotational velocities varied between 5.5 and 7.8 m/s. Fibre fracture and glass matrix particle detachment were the damage mechanisms observed by scanning electron microscopy. Composite wear was accompanied by material transfer onto the stator surface. The formation of isle-type and continuous graphitic films on the counter-body surface was observed. These films provide adequate lubrication during friction, leading to a relatively low wear of the composite under the conditions investigated.
Keywords: glass matrix composite; wear behaviour; self-lubricating composite; vacuum technology
Thermal Residual Stresses in Bonded Repairs by D. R. Daverschot; A. Vlot; H. J. M. Woerden (pp. 179-197).
The number of ageing aircraft is increasing and will further increase considerably in the near future. The control of damage by inspection and repair becomes therefore more and more important. The bonded repair method proved to be a cost-effective way to repair damage. However, this method has some disadvantages. One of them is the introduction of thermal residual stresses in the repair, due to the mismatch in coefficients of thermal expansion between the skin material and the repair material. Two analytical models are available to determine these residual stresses in the repairs, i.e., the Wang–Rose model and the Van Barneveld–Fredell model. A new computer program CalcuRep2000 [1] is being developed. This computer program will be used to calculate the stresses in bonded repairs, and is developed by the US Air Force in co-operation with the faculty of Aerospace Engineering of Delft University of Technology in The Netherlands. For this program an analytical model, which is able to calculate the thermal stresses in a bonded repair accurately, is essential. This paper describes how the most adequate analytical model was identified by comparison with Finite Element (FE) analysis. Two repair configurations were distinguished: The test specimen, i.e., bonded repair specimens used for fatigue tests in laboratories, and the in-field specimen, i.e., a realistic repair. The difference between both repair configurations is that a test specimen is free to expand during curing while in a realistic repair configuration expansion is partly prevented by the cooler surroundings of the heated area. The analytical model of Van Barneveld and Fredell proved to be the most accurate one. The results of this model agree with the results of the FE model of the test specimen and the in-field specimen. The Wang–Rose model calculates the thermal residual stresses accurately in the case of a test specimen, but the stresses calculated in the case of an in-field specimen are less accurate. No useful experimental data are available in literature from measurements of thermal residual strains on bonded repairs. Therefore experiments were conducted to measure thermal residual strains in bonded repairs. The same repair configurations were used for these experiments. The results obtained with the experiments are compared with FE results. Finally, the temperature distribution calculated by the analytical models is compared with the temperature distribution measured during the experiments of the in-field specimen. The influence on the thermal residual stresses of a different temperature field is discussed here, using the FE results.
Keywords: bonded repair; thermal residual stress; Glare; coefficient of thermal expansion (CTE)