Scaling effect in notched composites: The Discrete Ply Model approach

Abstract

Keywords:Size effect Open-hole tensile test Discrete Ply Modeling Experiments Finite element model a b s t r a c t Numerical and experimental investigations were carried out on the size effect in notched carbon/epoxy laminates. This paper presents a computational study of scaled open-hole tensile tests using the Discrete Ply Modeling (DPM) method, which has already proven efficient on both in-plane and out-of-plane loading cases, such as pull through, low velocity impact and compression after impact. The specificities of this finite element model are its discrete nature, the small number of parameters required and its robustness. Three different stacking sequences of thin plies coupled with three sizes of coupons having the same length to width ratio were tested. The results show that the model reflects the reduction in strength when the size of the specimen increases. The influence of different parameters such as mesh size, presence of discrete matrix cracks and fiber fracture toughness that should be used for clustered plies, are discussed.Comparisons with experiments demonstrate that tensile strengths, and failure scenarios and patterns are predicted with acceptable accuracy.

Validation and modeling of aeronautical composite structures subjected to combined loadings: The VERTEX project. Part 2: Load envelopes for the assessment of panels with large notches

“…For this model, the stress is averaged over this distance d 0 , called the ''average distance", in order to smooth the stress field in the surroundings of the hole/notch. One of the important issues generated by the study of holes and cracks is the scaling effect [7][8][9][10][11][12], which can be rendered by ''averaged stresses" type models even if the distance d 0 can depend on several factors [6], such as stacking sequence, material, and hole/notch size. The size effect leads, in particular, to a small hole being less penalizing than a large hole (for homothetic size of structures).…”

“…The size effect leads, in particular, to a small hole being less penalizing than a large hole (for homothetic size of structures). Numerous experimental and numerical investigations have been conducted in order to explain the physical meaning of the size effect [7][8][9][10][11][12]. For example, Wisnom et al [9,10] showed that the strength of notched composite laminates decreased when the notch size increased and concluded that the hole size effect was triggered by the presence of non-critical damage at the ply level, such as fiber failure, ply splitting, delamination or matrix cracking in the vicinity of the hole, smoothing the stress concentration.…”

“…The ratio of the size of this ''fracture process zone" to the specimen size explains the strength difference between small and large specimens. Recently, by using our own modeling strategies known as ''DPM" for Discrete Ply Modelling, we succeeded in capturing this size effect on open hole tensile specimens [12] and also on notched specimens [13]. This strategy was initially developed to simulate low energy impact on laminates [14,15] or pull-through [16].…”

“…This strategy was initially developed to simulate low energy impact on laminates [14,15] or pull-through [16]. Thanks to its unique capability to capture the failure scenario, the discrete nature of matrix cracking and inter-and intra-laminar damage coupling, this strategy was recently extended to in-plane issues [12,13,17]. In the present paper, this strategy will be extended to the issue of large notches under complex loading and will be recalled only very briefly below.…”

Validation and modeling of aeronautical composite structures subjected to combined loadings: The VERTEX project. Part 1: Experimental setup, FE-DIC instrumentation and procedures

“…The authors of these articles (the present article and its second part) initially developed the Discrete Ply Model method to deal with out-of-plane issues such as low energy impact [9,10] and pull-through [11]. This type of method is also efficient for in-plane stresses [12,13]. It is mainly based on a mesh imposing a priori rupture paths, which makes it possible to take splitting and intra and inter-laminar interactions into account.…”