Aspects of Damage Tolerance and Fatigue of CFRP Structural Components

Lightweight structures are one key issue for all future mobility concepts. Carbon fibre reinforced plastics (CFRP) play an important role in these disciplines due to their outstanding mechanical performance regarding to their weight. Therefore, CRFP structures have been widely used since decades in aerospace industry resulting in improvements in payload, fuel consumption and range. The Airbus A350, Boeing B787 in civil airplane industry as well as military products like the NH90 transport helicopter are examples of this development towards “all composite”-aircrafts with nearly all structural parts made out of composite materials. The increasing importance of electro mobility in the automotive sector leads to the necessity of new structural design approaches apart from commonly used metallic designs. The objectives are to reach adequate ranges by compensating for the additional weight due to electric components of hybrid or purely electric driven vehicles by improved lightweight structural design. The technological peak of this development are the i-models of BMW using CFRP for body-in-white-structure for the first time in commercial automobiles. A main difference of CFRP-structures towards metallic ones is the behavior regarding damage tolerance and fatigue. For helicopter composite structures this issue is newly defined in §573 of the relevant certification specifications (CS for EU, FAR for US) valid since December 2012. This paper for the first time summarizes the necessary efforts and possible methods to show compliance for this specific topic in the aerospace industry. As there is no similar specification or rule available now, this may serve as an example in other fields like the automotive industry. This paper discusses approaches used in aerospace industry to design robust and lightweight CFRP structural components, which can also be transferred to automobile structures. This includes definitions and standard practices defining the damage, generation of design allowables and necessary testing effort.