Metal Matrix Composite Plates Research Articles

On plastic zones and fracture strengths in some metal matrix composites

Based on a Dugdale-type approach for cancelling the singularity at the crack tip, an attempt was made to predict the overall stress distributions, as well as the size of the plastic zone found in notched metal matrix composite plate. The work was developed by considering notched, unidirectionally reinforced fibrous metal matrix composite plate under uniform normal tension load. Predictions of the proposed method were compared with the experimental results, and a fairly good agreement was observed. Simple closed form expressions for the local stresses and fracture strength are provided.

Production of flexible metal matrix composites reinforced with continuous Si-Ti-C-O fibers by atmospheric plasma spraying

An investigation of the production of aluminum matrix composite sheet reinforced with continuous Si-Ti-C-O fibers was performed by a plasma spraying method. The unidirectionally reinforced Si-Ti-C-O fiber/Al prepreg sheet (300 by 3000 mm, 0.1 to 0.15 mm thick, with 40 vol. % Fiber) was fabricated by plasma spraying under atmospheric conditions. The depth of the oxidation layer formed on the surface of the metal matrix composite (MMC) prepreg sheet was found to be about 200 A, and this value is almost independent of the atmosphere during plasma spraying. The fibers homogeneously disperse and do not contact each other in the matrix of the MMC prepreg. No damage on the surface of the extracted fibers from the MMC prepreg sheet can be observed. The MMC prepreg sheet was used to produce MMC plate by hot pressing at 640 to 680 °C under 9.8 MPa. The flexural strengths in the longitudinal and transverse directions of the MMC plate pressed at 660 °C were 1.0 and 0.25 GPa, respectively.

Fracture of fibrous metal matrix composites—IV. Plastic zones, local stresses and fracture strength

An analytical procedure for prediction of fracture strength in unidirectionally reinforced, notched metal matrix composite (MMC) plates is described. As in Parts I–III [ Engng Fracture Mech. 34, 87–104 (1989); 34, 105–123 (1989); 37, 1207–1232 (1990)], the objective is to evaluate the tension stress in a small volume of material ahead of the notch tip, while the composite plate is loaded in simple tension. In the composite systems considered in this study, fracture is typically preceded by formation of long, discrete plastic shear zones aligned in the fiber direction. The length of such zones is evaluated here by the crack interaction scheme proposed recently by Benveniste et al. [ Int. J. Solids Structures 25, 1279–1293 (1989)] and a Dugdale-type condition imposed at the end of the plastic zone. Then, the local tension stress ahead of the notch is found by superposition of a ligament stress and the stress induced by the shear tractions in the plastic zone. Comparison with numerous fracture strength measurements on notched B/Al and FP/Al plates confirms that the onset of fracture is associated with a critical magnitude of the local stress in a small volume of the composite material. The present procedure provides closed-form expressions for evaluation of the local stresses, and for fracture strength predictions in unidirectional MMC plates.

INELASTIC THERMAL BUCKLING OF METAL MATRIX LAMINATED PLATES

A method is proposed for determining the critical temperature changes that cause inelastic thermal bifurcation buckling of metal matrix composite plates. The inelastic behavior of the metallic matrix is described by an elastic-viscoplastic temperature-dependent constitutive law; the fibers are allowed to be either elastic or elastic-viscoplastic material. The approach is based on the applied thermal load and the history-dependent instantaneous effective thermomechanical properties of metal matrix composites, which are established by a micromechanical analysis. The method is illustrated by the prediction of the inelastic thermal buckling of SiC/Ti metal matrix angle-ply laminated plates by employing the classical and first-order shear deformable laminated plate theories.

Plastic buckling of metal matrix laminated plates

A method is proposed for the determination of plastic bifurcation buckling load of metal matrix composite plates. The metallic matrix behavior is described by an elastic-viscoplastic constitutive law, while the fibers are assumed to be either elastic or elastic-viscoplastic material. The approach is based on the load level and history dependent instantaneous effective properties of the inelastic plate, which are established by a micromechanical analysis. An incremental procedure is developed in which a buckling condition has to be established and its fulfilment must be checked at each increment. The method is applied for the prediction of the plastic buckling of boron/aluminum composite plates in various situations, by employing the classical and higher order shear deformation plate theories.