Abstract
The simplified automated strength model of a fragment of composite laminate at microlevel based on the finite elements (FE) method is offered. The model allows investigating the growth of microcracks which arise in the resin in monolayers, orthogonal to a direction of external tensile force. On the basis of automated strength FE model of a fragment of composite laminate and the method of reduction of stiffness characteristics of the resin, the scenario of growth of primary destructions at the microlevel is offered and proved. The scenario is confirmed with experimental investigations of composite samples under tension with registration of acoustic emission. In the work, the dependences of decrease of strength characteristics of composite laminates are obtained as functions of characteristics of resin, angles of orientation of monolayers, volume ratio of fibres in a composite laminate.
Highlights
Aircraft structures made of composite laminates, based on carbon reinforcing fibres, are considered as alternative to conventional primary metal structures for increasing weight efficiency of aircraft structures
The specified drawbacks are caused by a presence of plural stress concentrations at the microlevel, leading to occurrence and propagation of primary destructions in resin and the subsequent degradation of strength characteristics of composite laminates while in service
The nature of occurrence of such stress concentrations is caused by the topology of composite laminates, and the character of propagation of the cracks, arising in zones of the concentrations, is caused by low strength characteristics of resin
Summary
Aircraft structures made of composite laminates, based on carbon reinforcing fibres, are considered as alternative to conventional primary metal structures for increasing weight efficiency of aircraft structures. High sensitivity of composite laminates to impacts and climatic factors, their fragility and complex character of internal stress-strain state do not allow realising potential of high-strength carbon fibres and providing high weight efficiency of composite structures. For designing primary composite aircraft structures with high weight efficiency, meeting the requirements of long operation, it is necessary to have the reliable strength criteria considering occurrence of microcracks, their propagation and relation of these processes with strength of aircraft structure. Such strength criteria can be developed only on the basis of the extensive numerical and experimental investigations of strength of composite laminates, including investigations at microlevel. The given work is focused on the first steps in solving this problem
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