NUMERICAL MODELING OF DELAMINATION DURING MACHINING OF LFRP - PDF document

18 TH INTERNATIONAL CONFERENCE ONCOMPOSITEMATERIALS NUMERICAL MODELING OF DELAMINATION DURING MACHINING OF LFRP COMPOSITES X. Soldani 1, *, C.Santiuste 2 , J.L. Cantero 1 , M. H. Miguélez 1 1 Department of Mechanical Engineering Avda. Universidad 30, 28911, Leganés, Madrid, Spain 2 Department of Continuum Mechanics and Structural Analysis Avda. Universidad 30, 28911, Leganés, Madrid, Spain * Corresponding author( xsoldani@ing.uc3m.es ) Keywords : LFRP Composite, Numerical Modeling, delamination damage. 1 Introduction operations, mainly milling and drilling, previously to Long Fiber Reinforced Polymer (LFRP) the final assembly, in order to achieve dimensional composites, are widely used in different industrial specifications [2]. Machining can be considered a sectors due to their excellent mechanical properties dynamic process involving high cutting speed, and and lightness. extreme contact conditions at the interface tool-chip LFRP composites are the general terminology [3]. Both impact and machining process can induce to represent three main families of composites based irreversible damage in LFRP composites. Among on glass, carbon and aramid fibers (mainly Kevlar) the different damage mechanisms, delamination is in a polymeric matrix (commonly denoted GFRP, the main responsible of damage extension and loss CFRP and AFRP/KFRP respectively). Long fibers in residual properties. can be unidirectional or multidirectional (woven). Most works dealing with orthogonal cutting of Due to his competitive cost, Glass fiber reinforced composite materials, are based ontwo dimensional plastics (GFRP) are the most commonly used. numerical models and assume the hypothesis of Carbon fiber reinforced plastics (CFRP) and aramid plane stress [4,5]. However the onset and fiber (commonly Kevlar) reinforced plastics (AFRP) progression of delamination damage are dependent present better specific strength, higher specific on the matrix behavior when laminate is subjected to stiffness and lighter weight. CFRP composites are out-of-plane tensile and shearing stresses. Therefore widely used in structural components in aircrafts. two-dimensional analysis is not suitable for AFRPsreplace CFRPs when higher strength, predicting delamination. On the other hand, only lightness and toughness are required, for instance for unidirectional laminate can be modeled, while quasi- personal protections [1]. isotropic laminates are used in structural The use of these materials in different mobile applications due to their higher performance. systems in aerospace and naval applications justifies The implementation of 3D numerical models to the interest of understanding their behavior under predict out-of-plane damage induced on LFRP dynamic loading. The possibility of suffering an composite laminates after machining operations can impact of a foreign object is elevated in such lead to a better understand of the failure mechanisms applications. On the other hand, LFRP composites and delamination onset [5]. are also subjected to dynamic loading during the last In this paper, a 3D numerical model of stages of the component manufacture. Although the composite machining considering out-of-plane components are manufactured close to the final damage is presented and validated with experimental results obtained from literature. shape, they commonly require some machining

2 Damage modeling transversal strengths are dependent on the tensile or compressive stress state. Damage modeling is an important aspect for These models do not allow predicting the the accurate simulation of impact tests and different failure modes characterizing composite machining processes of LFRP composites. Among materials: fiber failure, matrix failure, and fiber- the different techniques available to predict matrix interface. This limitation has motivated the composite damage, the failure-criteria approach has formulation of more realistic failure criteria. The demonstrated its accuracy in both static and dynamic most common sets of criteria used in the analysis of loading states. Different failure criteria are proposed composite material in dynamic conditions are those in the literature [6]. due to Hashin [12] and Hou [13], constituting a The analysis of the different models available three-dimensional version of Chang-Chang criteria for long fiber composites and the identification of [14]. damage model parameters, have motivated an Both Hashin and Hou criterion consider international exercise developed between 1998 and different failure mechanism and equations. Four 2004 [7] comparing different failure criteria under failure modes (fiber failure, matrix cracking, matrix static conditions. No comparable study has been crushing and delamination) are accounted in Hou performed under dynamic loading. The most criteria, considering quadratic interaction between common failure criteria used in the dynamic stresses, see Table 1. Hashin formulation considers conditions can be categorized in ply criteria which also four failure modes: tensile and compression use an equation to predict the global failure of each failure of fiber and matrix, however delamination is ply, and complex criteria involving several failure not considered. A quadratic interaction between the modes (matrix cracking, matrix crushing, fiber components of the stress vector associated with the failure, delamination, etc). failure plane governs each mode. Although the complex failure of composite materials needs to distinguish between different 3 Numerical model failure modes, simple criteria have been used in A 3D numerical model of orthogonal cutting of several works to model the impact behavior [8,9] and the machining processes of composite materials LFRP was developed in ABAQUS/Explicit code. Dynamic explicit analysis was carried out using [10]. C3D8R, with 8-node brick elements with reduced The failure of composite materials cannot be predicted using Von Mises yield criterion that apply integration available in ABAQUS/Explicit [15]. A scheme of the numerical model is presented in Fig.1. only to isotropic materials. The failure of anisotropic Material behavior was modeled with a materials has been determined for many years by means of Hill criterion, which is an extension of VUMAT subroutine, including failure criteria, a degradation procedure and an element deletion Von Mises criterion to anisotropic materials. Tsai- criterion. The failure criteria used in based on 3D Hill criterion is based on the application of the strength parameters present in Hill criterion to the Hashin criteria formulation. Since Hashin criteria does not consider delamination criterion, Hou critical strength values in three orthogonal directions formulation [13] was used to complete failure formulating a criterion for LFRP composite, see Eq. 1 (X 1 and X 2 are the longitudinal and transversal criteria. When a failure criterion is verified mechanical properties are degraded according to strength respectively and S is the shear strength). failure mode. Fiber failure implies that all the 2 2 2 σ 1 2 − σ 1 σ 2 2 + σ 2 2 + σ 12 mechanical properties are degraded while matrix S 2 ≥ 1 (1) failure implies that only transverse mechanical are X 1 X 1 X 2 degraded. Delamination implies degradation of the out-of-plane mechanical properties.A procedure to Tsai-Wu criterion [11] is a modification of remove the distorted elements, based on the Tsai-Hill criterion taking into consideration different values for tensile and compressive strength. The maximum strain criterion was also implemented in the subroutine. formulation of Tsai-Wu criterion is the same given in Eq. 1, but the values of the longitudinal and