Damage analysis in composite materials and design of adhesive joints for composite structures

Interfacial debonding and damage evolution in composites. The local imperfect interface models were developed for the single spherical and cylindrical inclusion composites. In contrast with the classical results under perfect interface conditions, the strain and stress fields were no longer uniform in the inclusions. To facilitate using the results in micromechanics models, the average stress concentration factors and average Eshelby tensor were derived under imperfect interface conditions. Moreover, the energy release was also discussed for a single inclusion during interface deterioration.; Evolution of distributed damage in heterogeneous solids was modeled using the Transformation Field Analysis method and the selected models of interface debonding in fibrous or particulate composites. In this approach, stress changes caused by local debonding under increasing overall loads were represented by residual stresses generated by damage-equivalent eigenstrains that acted together with the applied mechanical loading program and physically based local transformation strains on an undamaged elastic aggregate. Interaction of the actual and equivalent eigenstrains with the mechanical loads at any state of damage was described by certain transformation influence functions which provide explicit expressions for the local stresses at any current damage state. Damage rates were then derived from a prescribed probability distribution of interface strength and local energy released by debonding. Numerical simulations of damage evolution in a glass/elastomer composite indicate which of these two conditions controlled the process at different reinforcement densities and overall stress states. In general, the energy released by a single particle at given overall stress decreased with increasing reinforcement density, and in proportion to particle size. Therefore, dense reinforcement by smaller-diameter particles should enhance damage resistance of composite systems.; Analysis and design of adhesive joints for composite structures . A new approach was explored for joining of thick, woven E-glass/vinyl ester composite laminated plates to steel or composite plates, with applications in naval ship structures. Adhesive was applied along through-the-thickness contoured interfaces, employing tongue-and-groove geometry. Both experimental and finite element modeling results were presented. They showed that adhesively bonded tongue-and-groove joints between steel and composite plates loaded in monotonically increasing longitudinal tension are stronger than conventional strap joints even in relatively thin plates. In particular, a single 0.25 in. wide and 8 or 12 in. long steel tongue, bonded by the Dexter-Hysol 9339 adhesive to a groove in a 0.5 in. thick laminated plate, can support a 20,000 lbs tension force. This force was expected to increase in proportion to plate thickness. Simple design rules indicate that the adhesive bond can be made stronger than that of the tongues, so that failure was transferred from the adhesive to the adherends. High joint efficiency can be achieved for any thickness of the joined plates.