Scaling effects in notched composites

Large composite structures can give much lower strengths than small coupons, and so a proper understanding of scaling is vital for their safe and efficient use. Small scale tests are commonly used to justify allowable stresses, but could be dangerous if results are extrapolated without accounting for scaling effects. On the other hand large factors are sometimes applied to compensate for uncertainties, resulting in overweight designs. Despite much research worldwide on failure, there are no methods capable of accurately predicting scaling effects in notched composites, and so a substantial amount of full size component and structural testing is currently required, which is very expensive. This project focused on determining the effects of specimen dimensions on the unnotched and notched tensile and compressive strength of the IM7/8552 composite
through a carefully designed experimental programme, identifying and understanding the different factors influencing strength as a function of specimen size and modelling the behaviour by analytical and finite element analyses. Finally, examining the stacking sequence effects on failure strength using two different scaling techniques: sub-laminate-level ([45/90/-45/0]ns) and ply-level scaling ([45n/90n/-45n/0n]s).The research has led to major advances in understanding of notched failure. Models developed at Bristol can successfully predict tensile scaling effects from fundamental, independently measured material properties [1-2]. The results and models developed at Sheffield provide a better understanding of notched behaviour under compressive loading [3, 4].