Composites Engineering最新文献

This work provides a three-dimensional numerical fracture mechanics analysis of a crack periphery as it propagates through a brittle matrix and encounters an individual brittle fiber. The surface integral method, based upon a distribution of singular fundamental solutions, is used to represent both the cracks and the coupled interfacial sliding zone. The interfacial frictional tractions are assumed to satisfy a Coulomb relationship and are determined iteratively from the stress induced by the matrix crack, the stress induced by the developing slip, and the initial normal compressive interfacial stress (i.e. from setting or thermal mismatch). Simulations of an initially long straight crack front moving toward and past a fiber for different interfacial frictional characteristics were conducted. The implications for tailoring fiber/matrix interfaces to optimize the global toughening effect are discussed. If the interface between fiber and matrix is cohesive enough (but not too cohesive) then tractions which develop at the interface may effectively retard the local growth of a matrix crack. Raising the friction coefficient (or cohesion) at the interface must, however, be balanced against the potential for fiber failure in the high stress zone near the matrix crack periphery. The implications frictional slippage holds for inhibiting and possibly arresting small matrix cracks are emphasized.

Transient response of a moving composite laminate suddenly subjected to combined mechanical load and high intensity laser irradiation was investigated. The three thermal effects, which are caused by rapid laser heating and influence the structure's dynamic behavior, are material property degradation, burn-out and induced thermal loading. To determine temperature distribution and material burn-out due to the high laser energy deposition, a modified Crank-Nicholson finite difference scheme, which includes the effects of surface ablation, degradation of thermophysical properties at elevated temperatures and heat losses from radiation and convection, was employed. The predicted thermal results were then used for thermal loading calculation and, subsequently, forced vibration analysis. Both small and large deflection composite plate theories were adopted. The inclusion of temperature-dependent mechanical properties in the analysis was also of particular importance. It was shown that the escalation or reduction of vibration response of a laminated composite subjected to transverse loads by laser irradiation depends not only upon the laser intensity, but also, which plate surface is irradiated. It was also found that a higher power laser irradiation ensures neither greater escalation not reduction of the vibration.

A consistent higher-order analysis is presented for the shock response of doubly-curved cross-ply laminated thick panels simply supported on four edges. Emphasis is laid on consistency with the three-dimensional boundary conditions and interlaminar stress continuity, respectively. In each layer, a three-dimensional dynamic displacement field is assumed in terms of in-plane double Fourier series and cubic polynomials in the thickness direction. A system of modified Lagrange equations is derived via an energy variational approach with all surface conditions, and interlaminar continuity included. Modal analysis is performed for the shock response using a modified exponential decay overpressure. Three-dimensional displacements and stresses can be found any time throughout the panels. Present results, including frequency spectra of σ33, are perfectly consistent with existing wave theory without prior assumption of wave motion.

Multilayered metal base composites, mainly reinforced with steel sheets, were fabricated using the single-shot explosive welding technique. Plate velocity change during the collision of multilayered plates within small stand-off distances were analyzed using a one-dimensional finite-difference calculation, and the explosive welding parameters required for good bonding were investigated. Wavy interfaces, which suggest good bonding, were found in the case where properties, such as density, strength and melting point, of the bonded materials were not so different, but excess melting, poor bonding and planar interfacial structure were observed when the properties of the materials used were considerably different. In the case where properties of the materials were fairly different, the weldable condition for good bonding was restricted. In this investigation, the way to regulate the explosive welding parameters for good bonding and the welding mechanisms were discussed, and the mechanical properties of the composites measured by tensile tests were investigated based on the rule of mixtures.

This paper discusses two potential ultrasonic methods for characterization of fiber-matrix interphases in composites: measurement of phase velocity and attenuation. The characterization procedures of these two methods, including different implementations using analytical or numerical models, are reviewed with emphasis on the applicability of these methods. Examples of ultrasonic characterization of interphases in ceramic and intermetallic matrix composites are given and the relation between the measured and actual interphase moduli is discussed. Application of these techniques for interfacial damage assessment is also demonstrated, including characterization of oxidation damage in ceramic matrix composites and fatigue damage in metal matrix composites. The experimental results show that degradation of the interphasial layer significantly affects ultrasonic wave attenuation and velocity. Thus both methods are very useful for assessment of interfacial damage.

Theoretical fundamentals for a 2D layer-wise laminate theory including the transverse shear and transverse normal strains are presented which provide a compromise between the continuum theory and the single-layer laminate theories. Four-node isoparametric assumed strain layer-wise shell elements are developed which can be applied to interlaminar stress analysis of composite laminates and simulation of stress singularities due to concentrated loading, freeedge effects, etc. Numerical examples are given to demonstrate the ability and accuracy of the numerical models proposed.

This paper investigates the low cycle fatigue and fracture behavior of cast-then-hot-extruded 6061 aluminum reinforced with alumina particles. The effect of heat treatment and volume percentages of the particle (0–20%) on the axial fatigue behavior and fracture toughness was investigated. Cyclic hardening of the under-aged and the peak-aged samples was observed while cyclic softening of the over-aged specimens was recorded. Although fatigue data follow the Coffin-Manson's model, the fatigue resistance of the composites was lower than that of the matrix alloy regardless of aging and percentage of the reinforcement. Plane strain condition was marginally achieved due to insufficient sample thickness. The measured fracture toughness for these composites however was low compared with that of the matrix alloy and decreased with increasing reinforcement content. Scanning electron microscopy reveals that a crack starts at a machine defect and propagates through or avoids a particle depending on the relative position of the crack front and the particle. Three failure modes were found for this advanced material: cleavage fracture of a particle, cohesive delamination between matrix and particle and void coalescence in the matrix.