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A new numerical model combining LaRC failure criterion and extended finite element method (XFEM) is created to describe the failure behavior in fiber-reinforced polymer (FRP) composites. In this model, the onset of intralaminar damages are predicted based on the LaRC failure criterion, and the crack propagation and stiffness degradation are described explicitly by the XFEM. The user subroutine UDMGINI of ABAQUS defines the initial damage criterion and a mixed-mode, energy-based fracture criterion is employed to describe the crack onset and propagation in the enriched region of XFEM. The proposed model is used to investigate the failure behavior of two sets of open-hole laminates under tension. It is demonstrated that the proposed numerical method can predict the experimental data well. [ABSTRACT FROM AUTHOR]

Natural fibers and their composites differ in several aspects with carbon fibers, including higher scatter in strength and different tensile responses. The tensile and bending properties of flax fiber composites were experimentally studied and numerically simulated. Composite panels were fabricated from unidirectional flax fiber tapes and polypropylene films via hot pressing technique. The variation in the properties of flax/polypropylene composites was found to be relatively moderate as compared with that of single natural fibers. A multi-scale finite element analysis (FEA) strategy for the progressive damage prediction of natural fiber composites was developed. The FEA model started from micro-scale analysis which predicted the effective properties of unidirectional flax ply through representative volume element. Macro-scale analysis was conducted subsequently to predict the properties of composite coupons using the results of micro-scale analysis as inputs. The developed multi-scale FE model successfully predicted the tensile strength, bending behavior, and major failure modes of flax/polypropylene composites. [ABSTRACT FROM AUTHOR]

Braided textile composite exhibits an efficient mechanism to distribute loads throughout its structure and have excellent impact resistant properties. Despite many works in the past, the successful prediction of braided textile composites strength still remains a challenge today. In this paper, a numerical simulation model based on a meso-scale approach is presented to predict the strength and damage behavior of braided textile composites. A meso-scale homogenized representative unit cell was built for the study using finite element analysis (FEA) method. 3D-Hashin and Stassi failure criteria were respectively selected for the yarn and the pure matrix, and coded in a subroutine in Abaqus finite element solver to study the individual constituents damages. From the different numerical studies, the failure mechanisms were observed to change with the braiding angle. The meso-scale computed results were also seen to agree closely with experimental and simulation results computed using a micro-mechanics failure approach. [ABSTRACT FROM AUTHOR]

In recent years, short fiber reinforced thermoplastic composites (SFRTPCs) have attracted significant interest due to their low density, high strength and toughness, environmental resistance and low cost. Currently, an important task is to optimize their internal structures so as to maximize their mechanical properties. Interestingly, a previous experimental study showed that by adding a small amount of a stronger material in the matrix to link up short fibers, the strength of SFRTPCs was enhanced. We note, however, that a micromechanical study on the effect of fiber linkage on the mechanical properties is still lacking. In this work, we have developed a finite element model to conduct such micromechanical analysis. In this model, the polymer matrix is taken as elastic-plastic material, the fiber as a brittle material following a brittle damage model, while the interphase and linkage as the same polymer following a progressive damage model. Our simulations show that for a SFRTPC with a given short fiber weight fraction, by increasing the weight fraction of the linkage material, the Young's modulus, yielding strength, ultimate tensile strength, and tensile toughness of the SFRTPCs are all increased. By increasing the strength of the linkage material, the ultimate tensile strength and tensile toughness of the SFRTPCs are increased. Modified rules of mixing have been proposed to consider the fiber crosslinking effect. The present study provides a useful reference for the optimal design of SFRTPCs to maximize their mechanical performance. [Display omitted] [ABSTRACT FROM AUTHOR]

Depending on fiber size and volume fraction, polymer matrix type, processing temperature, injection speed, etc., short fiber reinforced composites produced by injection molding may exhibit complex fiber concentration, orientation and length distributions at different locations, causing large variations in their mechanical properties. In this work, a representative volume element (RVE) scheme is developed to describe the elastic properties of short glass fiber reinforced PA6,6 composites produced by injection molding. In the RVE formulation, fiber length is assumed to follow a two-parameter Weibull distribution, and a new concept, namely preferential angle, is introduced to account for the preferential alignment of fibers at different locations of injection molded composites. A random sequential insertion algorithm is developed to implement the fiber length distribution and fiber preferential alignment, and finite element method (FEM) is employed to analyze the relations of the elastic properties of RVE with three parameters, that is, the mean length, volume fraction and preferential angle of the fibers. Based on the FEM results, quantitative formulas for these relations are obtained. It is found that the variations in the mean length, volume fraction, and preferential angle of the fibers can cause large variations in elastic moduli and elastic anisotropy of the RVE. [ABSTRACT FROM AUTHOR]

The article Prediction of the mechanical behavior of flax polypropylene composites based on multi-scale finite element analysis, written by Yucheng Zhong, Le Quan Ngoc Tran, Umeyr Kureemun, and Heow Pueh Lee, was originally published Online First without open access. [ABSTRACT FROM AUTHOR]

• A novel concurrent multi-scale damage evolution modeling scheme with high computational efficiency is proposed for the design and analysis of 3D angle-interlock woven composites. • The proposed model is successfully validated by off-axis tensile test of 3D woven composites with the help of 3D DIC method. • Full range tensile analyses (different on-axis and off-axis angles) are conducted using the validated model to study the mechanical response and damage mechanisms of 3D angle-interlock woven composites. Computational models with high precision and efficiency are in urgent need for the damage analyses of 3D angle-interlock woven composites which are widely accepted in composites industry. A novel concurrent multi-scale damage evolution modeling scheme is established based on a meso-scale representative volume cell (RVC) model and the multiphase finite element method to characterize the off-axis tensile response of carbon/epoxy composites. Modified Puck criterion and maximum shear stress criterion are adopted for fiber yarns. Parabolic yield criterion is adopted for the matrix. The fiber breakage, the inter-fiber fracture and matrix cracking are considered at mesoscopic level. To validate the proposed multi-scale damage model, off-axis tensile test is conducted with the help of 3D Digital Image Correlation (DIC) method. A reasonably good agreement is achieved between numerical predictions and experimental observations. Furthermore, the validated damage model is used to predict the tensile response of the composites considering full range on-axis and off-axis angles. [Display omitted] [ABSTRACT FROM AUTHOR]

The thermal residual stresses (TRSes) can noticeably increase the yield strength and flow stresses of particle-reinforced metal-matrix composites (PR-MMCs) and show size-dependence due to thermal geometrically necessary dislocations (GNDs) when the size of particles is on the order of micron. This TRSes strengthening is attributed to the conventional thermal-elasto-plastic constituent mismatch (regardless of particles’ size) and the presence of GNDs (size-dependent). A modified Taylor-based nonlocal theory (TNT) of plasticity is proposed to quantify the individual contributions of size-dependent GND strengthening. An axisymmetric unit-cell model of uniform and aligned particle distribution with various particle sizes is built to study thermal-induced non-uniformly distributed GNDs, their evolution and contributions to the stress strengthening under combined thermal and mechanical loading. The results show that the proposed methodology can effectively capture the size dependence of thermal-induced GNDs which keeps a sharp gradient variation in the zone near the matrix-inclusion interface and gradually flattens out in the zone far away from the interface. It is demonstrated that TRSes significantly improve the yield strength and flow stresses. It also revealed that the contribution of thermal-induced GNDs increased as the particle size in the PR-MMCs decreased. The simulation results were validated by experimental results reported in the literature. [ABSTRACT FROM AUTHOR]

Laminated composites with thin-ply unidirectional prepregs are popular due to their higher in-situ strength as compared with thick-ply laminates due to different failure mechanisms. Thin-ply and thick-ply open-hole laminates were fabricated and the tensile failure characteristics were studied by combining experimental and numerical simulation approaches. Charge-coupled device camera and de-ply technology were used to obtain failure morphologies of open-hole specimens under tensile loading. A finite element model considering progressive damage and bilinear cohesive model was built based on ABAQUS to study the damage mechanism of open-hole laminates. In thin-ply laminates, the damage plane was relatively neat while in thick-ply laminate broom-shaped damage morphologies were observed. Based on de-ply experiments and numerical prediction, it was found that thin-ply laminates had delamination suppression effect and could restrain the propagation of delamination along the loading direction, which explains the distinct damage patterns existed in thin-ply and thick-ply laminates. Based on numerical prediction, it was found that drilling-induced delamination did not affect the tensile strength of open-hole laminates. Propagation of drilling-induced delamination was also restrained in thin-ply laminates. The results of this research suggested that thin-ply prepregs should be considered when delamination poses critical threat to the structural integrity of laminated composite structures. • A progressive damage model considering LaRC 05 failure criterion is proposed and implemented via an in-house VUMAT code. • Damage evolution of open-hole laminates fabricated using thin-ply prepregs under tensile loading is studied. • Advantages of thin-ply laminates and underlying mechanisms are studied and proved. • Effects of drilling-induced delamination on the mechanical properties of laminated composites are discussed. [ABSTRACT FROM AUTHOR]