PSI - Issue 60

Rajagurunathan M et al. / Procedia Structural Integrity 60 (2024) 517–524 Rajagurunathan and Prakash./ Structural Integrity Procedia 00 (2024) 000–000

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Low velocity impact on composites, such as tool drop during maintenance and run way debris impact, may create internal damages like matrix damage, delaminations and fiber breakage due to longer impact duration [Shi et al, (2012)]. These damages can be challenging to detect by naked eyes, but, can significantly reduce the strength and stiffness of the structure. Delamination is one of the most dangerous damage mechanisms for composites since it affects the matrix dominated properties. This can occur due to out-of-plane loading conditions, impact loading, or even in-plane tensile-tensile fatigue loading situations in the final failure stages [John et al. (2018); Camanho et al. (2007)]. Therefore, the damage resistance of composite laminates under low velocity impact and its residual strength are very important in the design of composite structures [Tuo et al. (2019); Yang et al. (2021); Anuse et al. (2022)]. To meet the certification requirements of these composite structures, extensive and expensive characterization and trial-and-error testing are required. To minimize the experimentation effort, it is necessary to develop a virtual experimental testing model using finite element method to analyze the impact resistance and residual strength of the composite structures. Generally, the numerical simulations play a major role in engineering development behind the experimental investigations. Once the numerical model is validated properly, it is possible to do the parametric studies with different geometries, materials, loading conditions and stacking sequences. Many researchers have studied the low velocity impact behavior of carbon fiber reinforced composite laminates by means of analytical, empirical and numerical modelling. Bouvet et al. (2012) performed an experimental study and developed a numerical model to predict the damage in carbon/epoxy laminates under low velocity impact. Matrix cracking, fiber failure and delamination were predicted successfully in their study. Sellito et al. (2019) had developed a finite element model with user subroutine VUMAT to analyze the impact induced damages in CFRP laminates. The results obtained from continuum shell element (SC8R) and solid elements (C3DR) were validated with their experimental results; the study identified that the solid element model gave a more realistic results compared to shell elements. Tuo et al. (2019) had performed a numerical study on quasi isotropic [0 2 /45 2 /90 2 /-45 2 ] s laminated plate of T700GC/M21 carbon/epoxy and reported that the drop in force-time curve or force-displacement curve predominates fiber failure due to tension. The authors further found that the fiber compressive failure occurred only at the upper ply. Lopes et al. (2009) had developed a model based on LaRCO4 model to investigate fiber and matrix damages in CFRP laminates with different stacking sequences. Zhou et al. (2019) established a 3D finite element model to study the damage development in CFRP cross-ply laminates under three different energy levels. In their model the 3D Hashin criterion and damage evolution, including, the through-the-thickness normal stress were proposed. The study concluded that the results are more realistic due to through-the-thickness stress in the damage propagation model. Zhang et al. (2021) developed a numerical model which included fiber kinking and transverse fracture angle with cohesive elements to investigate the low velocity impact (LVI) and compression after impact (CAI) on CFRP. It was evident from their study that, the delamination is a dominant failure mode than fiber and matrix damage under LVI. Anuse et al. (2022) performed a numerical and experimental study on QI laminates with different stacking sequence to predict the damage and deformation behavior. It was observed that the matrix cracking occurs in the top and middle laminae due to transverse shear stress and the matrix damage occurs due to tension at bottom plies. Also, no delamination was found between two laminae with same fiber orientation. In this work, a numerical model is developed using ABAQUS® to study the low impact behavior of CFRP laminates based on continuum damage model. The 2-D Hashin damage model – a built-in module- of ABAQUS® was used to predict the damage initiation. A cohesive surface-based model was selected to study the inter-laminar damages. The results of force time, energy-time and load-displacement histories are compared for cross-ply and quasi-isotropic laminates. 2. Simulation methodology of low velocity impact 2.1. Damage model for a composite lamina Each lamina in a composite laminate is generally considered as a transversely isotropic material with five independent material constants. The composite material exhibits linear elastic behavior before damage initiation; the constitutive law is represented as, { } = [ ]{ } where [ ] is elasticity matrix. In this simulation, progressive damage model is used to reduce the stiffness of composite materials depending on damage initiation criteria and evolution behavior. When failure occurs at a point on a composite material, its properties will change according to any of the material property degradation models, as shown in Fig.1. For this numerical study, a linear gradual degradation model is used to describe the behavior of a composite laminates [Zhang et al. (2021), Yang et al. (2021)].