Internal geometry of structurally stitched NCF preforms

Internal geometry of a textile reinforcement is an important factor of the reinforcement performance during the composite manufacturing and service life. In this article, generalized geometrical models of structural stitching loops are presented for the sewing, tufting, and dual-needle stitching methods. The term 'structural' presumes here that the stitching yarn does not only consolidate the plies (as the non-structural one does) but forms also a through-the-thickness (3D) reinforcement. The models account for the general features of the yarn loop geometry and are believed to allow for enough precise modelling on the meso-scale (textile unit cell) level. The modelling approach is validated with experimental data

A statistical treatment of the loss of stiffness during cyclic loading for short fiber reinforced injection molded composites

Injection molded short fiber reinforced composites (SFRC) have different local fiber orientation distribution (FOD) at every point. SN curves of short fiber reinforced composites are known to depend on the fiber orientation distribution. Such materials also suffer from continuous loss of stiffness during cyclic loading. It is not known whether the loss of stiffness is different for SFRC with different FOD. A statistical analysis of the loss of stiffness curves is presented in this paper. Tension-tension fatigue experiments are performed and loss of stiffness is collected for every data point in the SN curve. A systematic method for comparing the loss of stiffness is developed. It is concluded that the difference in loss of stiffness curves for coupons of SFRC with different FOD is not statistically significant. (C) 2016 Elsevier Ltd. All rights reserved

Protection Against Secondary Fragmentation From AP Mines Based on Natural Fibre Composites

The 1997 Ottawa Convention defines a mine as a munition designed to be placed under or near the ground or other surface area and to be exploded by the presence, proximity or contact of person or a vehicle. An AP mine is defined as a mine designed to be exploded by the presence, proximity or contact of a person and that will incapacitate, injure or kill one or more persons

Finite element modelling of inter-ply delamination and intra-yarn cracking in textile laminates

The aim of the current study is to demonstrate the effect of inter-ply delamination on stiffness degradation of multi-ply woven composites. Such a demonstration becomes possible due to new technique of modelling textile laminates. It is based on set of boundary value problems for unit cell of a single ply, where boundary conditions imitate interaction with the other plies. Once these problems are solved, local stress distribution and stiffness of the laminate are determined analytically as function of number of the plies and local stress/strain fields obtained in these problems. Hence, it opens the road for an efficient modelling of delamination, which is described as gradual reduction of plies in the laminate

Progressive fatigue damage modeling of textile composite on meso-scale with FE-method

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Research in textile composites at KU, Leuven

An overview is presented of the research on textile composites at Katholieke Universiteit Leuven. Three dimensionally woven sandwich fabric preforms are investigated for delamination resistant sandwich structures, velvet woven 2.5 dimensional fabrics for delamination resistant laminates, and knitted fabrics with good drapability for laminates of complex shape

FE-modeling of damage of twill carbon/epoxy composite on meso-scale, materials characterization and experimental verification

Aim of this work is to evaluate the damage in twill carbon/epoxy composites on meso-scale level (fabric unit cell level). Averaged stiffness, Poisson ratios of pre- and post damage phase are calculated based on numerical homogenization technique with periodic boundary conditions (PBCs). The static strengths and initiation of the damage are calculated and validated by experiments. The anisotropic stiffness degradation model is implemented into Abaqus (R) UMAT. The algorithm of quasi-static damage is further used to model the cycles of the fatigue loading, together with the experimental S-N curves of unidirectional composite (UD), utilized as input data for the impregnated yarns. The output of the model is S-N curve of textile composites

A feasibility study of the Master SN curve approach for short fiber reinforced composites

Short fiber reinforced composite (SFRC) materials have a different fiber orientation distribution (FOD) at every point. The fatigue properties of SFRC are known to depend on the FOD. The Master SN curve (MSNC) method for predicting an SN curve for a given FOD based on the known SN curve for the reference FOD is used to predict the local SN curve of a SFRC component by relating the damage at the microscopic level to the macroscopic fatigue properties. A simplified version of MSNC method, which needs even less experimental input, uses an assumption of constant SN curve slope is also presented in this paper. The paper validates both variants of the MSNC method on three sets of experimental data on fatigue of short fiber composites and analyses their accuracy. It is demonstrated that the MSNC approach needs only one SN curve as input with no specific requirements to the fiber orientation of the test coupon. Test coupons could have either uniform fiber orientation in the thickness or a "skin core" orientation variation. (C) 2016 Elsevier Ltd. All rights reserved

Tensile Behavior of Environment Friendly Jute Epoxy Laminated Composite

AbstractJute fiber has gained interest in the composite field due to its superior specific properties compared to manmade synthetic fibers like glass, kevlar, asbestos, etc. In this study, jute composites were made with the vacuum assisted resin infiltration (VARI) techniques having jute fiber preform staking sequences (0/0/0/0), 0/+45°/-45°/0 and 0/90°/90°/0. For all cases, a total of 25% volume fraction of jute fiber was incorporated. The developed composites were characterized by tensile and three point bend tests and the experimental results thus obtained were compared with that of the theoretical values. After both mechanical tests, fracture surfaces were cut and observed under high resolution FEG SEM (field emission gun scanning electron microscopy). In the case of 0/0/0/0 and 0/+45°/-45°/0 laminate, longitudinal tensile strength has been found to be higher than that of the transverse direction. However, for 0/90°/90°/0 laminate, tensile strength in both directions have been found to be very close to each other. For all developed composites, experimental results revealed that the tensile properties of the developed composites are strongly dependent on the tensile strength of jute fiber and that the tensile properties of jute fiber are very much defect sensitive. Finally, initiative has also been taken to discuss the mechanical behaviors of the composites in terms of the fracture morphologies observed under the SEM