Cracks, microcracks and fracture in polymer structures: Formation, detection, autonomic repair

Abstract

Polymers and polymer composites are susceptible to premature failure due to the formation of cracks and microcracks during their service time. Evolution of cracks and microcracks could induce catastrophic material failure. Therefore, the detection/diagnostics and effective repair of cracks and microcracks are vital for ensuring the performance reliability, cost effectiveness and safety for polymer structures. Cracks and microcracks, however, are difficult to detect and often repair processes are complex. Biologically inspired self-healing polymer systems with inherent ability to repair damage have the potential to autonomically repair cracks and microcracks. This article is a review on the latest developments on the topics of cracks and microcracks initiation and propagation in polymer structures and it discusses the current techniques for detection and 2 observation. Furthermore, cracks and microcrack repair through bio-mimetic self-healing techniques is discussed along with surface active protection. A separate section is dedicated to fracture analysis and discusses in details Fracture mechanics and formation.

Conductive and flexible multi‐walled carbon nanotube/polydimethylsiloxane composites made with naphthalene/toluene mixture

“…Also, the hysteresis for the composites with dispersing agents is more significant than for the composites without dispersing agents. The hysteresis may be caused by various mechanisms . A possible reason for the larger hysteresis of the composites with the dispersing agent may be that evaporation of the dispersing agents during and after curing can cause holes and microcracks in the composite.…”

Mechanical, dielectric, and physicochemical properties of impregnating resin based on unsaturated polyesterimides

“…Therefore, the material is constantly subjected to internal stresses of expansion and compression, due to the important dilatation of the resin, which could then contribute to ageing acceleration of the resin and potentially induce microcracks. Many studies deal with microcracking induced by mechanical fatigue (mechanical cycling) [33][34][35][36] at the origin of increase in the DP probability of occurrences.…”

Low‐velocity impact behavior of a carbon/bismaleimide composite proposed for supersonic flight simulation after hygrothermal cycling

“…In summary, the decrease of b indicates that the fiber/matrix interface of C/BMI composite was damaged slightly during the 300 hygrothermal cycles. It is well known that the interfacial damage caused by thermal cycling is due to the thermal stress induced by difference in CTE of fiber and matrix, along with the inherent residual stress of the composite . The increase of T g shows that the effects of hydrothermal ageing such as hydrolysis and plasticization were eliminated as a result of the complete dry off of the absorbed moisture during the high temperature period of the hygrothermal cycling.…”

“…Due to the difference in coefficients of thermal expansion (CTE) of carbon fiber and the BMI matrix and the mismatch in CTE between plies of the composite with different orientation, great thermal stress would generate within the C/BMI components during thermal cycles . This cyclic thermal stress along with the inherent residual stress might induce interfacial debonding and microcracking, also resulting in degradation of mechanical properties of the composite such as transverse tensile strength (TTS), flexural strength, ILSS, and compression strength . Gao and co‐workers attributed the degradation in TTS, ILSS, and flexural strength of unidirectional fiber‐reinforced composite to the combined effects of the matrix outgassing and interfacial debonding caused by vacuum thermal cycling.…”