C. Santiuste

Computational analysis of temperature effect in composite bolted joints for aeronautical applications

This study focuses on the analysis of influence of temperature and bolt torque on aeronautical joint behavior. A single-lap joint, according to ASTM D5961, with a titanium bolt and composite plates was considered. A numerical model based on FEM was developed to evaluate the stress in both bolt and composite plates. Load—displacement curves, stress fields, and induced damage showed, significantly, the influence of temperature combined with torque level on the joint. It was found that in the plate, both maximum and minimum levels of torque considered produced damage above critical threshold. This fact should be accounted for, during the design process of the joint.

A review on recent advances in numerical modelling of bone cutting.

Common practice of surgical treatments in orthopaedics and traumatology involves cutting processes of bone. These operations introduce risk of thermo-mechanical damage, since the threshold of critical temperature producing thermal osteonecrosis is very low. Therefore, it is important to develop predictive tools capable of simulating accurately the increase of temperature during bone cutting, being the modelling of these processes still a challenge. In addition, the prediction of cutting forces and mechanical damage is also important during machining operations. As the accuracy of simulations depends greatly on the proper choice of the thermo-mechanical properties, an essential part of the numerical model is the constitutive behaviour of the bone tissue, which is considered in different ways in the literature. This paper focuses on the review of the main contributions in modelling of bone cutting with special attention to the bone mechanical behaviour. The aim is to give the reader a complete vision of the approaches commonly presented in the literature in order to help in the development of accurate models for bone cutting.

Delamination prediction in orthogonal machining of carbon long fiber-reinforced polymer composites

Machining processes of composites are common operations in industry involving elevated risk of damage generation in the workpiece. Long fiber reinforced polymer composites used in high-responsibility applications require safety machining operations guaranteeing workpiece integrity. Modeling techniques would help in the improvement of machining processes definition; however, they are still poorly developed for composites. The aim of this paper is advancing in the prediction of damage mechanisms involved during cutting, including out-of-plane failure causing delamination. Only few works have focused on three-dimensional simulation of cutting; however, this approach is required for accurate reproduction of the complex geometries of tool and workpiece during cutting processes. On the other hand, cohesive interactions have proved its ability to simulate out-of-plane failure of composites under dynamic loads, as impact events. However, this interlaminar interaction has not been used up to date to model out-of-plane failure induced during chip removal. In this paper, both a classical damage model and cohesive interactions are implemented in a three-dimensional model based on finite elements, in order to analyze intralaminar and interlaminar damage generation in the simplified case of orthogonal cutting of carbon LFRP composite. More realistic damage predictions using cohesive interactions were observed. The strong influence of the stacking sequence on interlaminar damage has been demonstrated.

Modelling thermal effects in machining of carbon fiber reinforced polymer composites

Machining-induced damage is commonly observed when manufacturing components based on carbon fiber reinforced polymer (CFRP) composites. Despite the importance of thermal effects in machining CFRPs, this problem has been poorly analyzed in the literature. Predictive tools are not available for thermal phenomena involved during cutting, while only few experimental studies have been found. In this paper, a three-dimensional (3D) finite element model of orthogonal machining of CFRPs including thermal effects is presented. Predicted thermal and mechanical intralaminar damage showed strong influence of fiber orientation. Thermally affected area was larger than mechanically damaged zone. This fact confirms the importance of accounting for thermal effects when modelling CFRP machining.

Theoretical Estimation of Thermal Effects in Drilling of Woven Carbon Fiber Composite

Carbon Fiber Reinforced Polymer (CFRPs) composites are extensively used in structural applications due to their attractive properties. Although the components are usually made near net shape, machining processes are needed to achieve dimensional tolerance and assembly requirements. Drilling is a common operation required for further mechanical joining of the components. CFRPs are vulnerable to processing induced damage; mainly delamination, fiber pull-out, and thermal degradation, drilling induced defects being one of the main causes of component rejection during manufacturing processes. Despite the importance of analyzing thermal phenomena involved in the machining of composites, only few authors have focused their attention on this problem, most of them using an experimental approach. The temperature at the workpiece could affect surface quality of the component and its measurement during processing is difficult. The estimation of the amount of heat generated during drilling is important; however, numerical modeling of drilling processes involves a high computational cost. This paper presents a combined approach to thermal analysis of composite drilling, using both an analytical estimation of heat generated during drilling and numerical modeling for heat propagation. Promising results for indirect detection of risk of thermal damage, through the measurement of thrust force and cutting torque, are obtained.

Numerical analysis of the ballistic behaviour of Kevlar® composite under impact of double-nosed stepped cylindrical projectiles

This paper focuses on the numerical analysis of the ballistic performance of Kevlar®-29 under impact of different double-nosed stepped cylindrical projectiles. Numerical modelling based on finite element method was carried out in order to predict the failure mode of the target as well as the ballistic limit. A detailed analysis of the ballistic limit, failure mode and deformation of the targets due to impact of double-nosed projectiles was developed, discussed and compared with those involved in penetration of single-nosed flat and conical projectiles. Significant influence of the projectile geometry was demonstrated: the lowest ballistic limit was obtained with the conical–conical nose shape projectiles.

Perforation of Composite Laminate Subjected to Dynamic Loads

This chapter focuses on the modeling of plain woven GFRP laminates under high-velocity impact. A brief review of the different approaches available in scientific literature to model the behavior of composite laminates subjected to high-velocity impact of low-mass projectiles is presented, and a new analytical model is proposed. The present model is able to predict the energy absorbed by the laminate during the perforation process including the main energy-absorption mechanisms for thin laminates: kinetic energy transferred to the laminate, fiber failure, elastic deformation, matrix cracking, and delamination.

2D and 3D approaches to simulation of metal and composite cutting

Numerical modeling of machining is an active research field in manufacturing. Despite of the improvement of computers, 3D modeling has still high computational cost. 2D modeling has been extensively used for decades in the prediction of difficult to measure variables in metal cutting. On the other hand long fiber reinforced composites are extensively used in industry; however the numerical modeling of composite cutting is still poorly developed, and mainly focused on 2D approach. Two dimensional approaches imply some simplifying hypotheses those could influence the results obtained from the analysis. In this paper a comparison between 2D and 3D modeling of both metal and composite orthogonal cutting is presented. The aim of the paper is analyzing the validity of the hypothesis involved in 2D modeling comparing with the results obtained from 3D approach.

Experimental analysis of drilling induced damage in biocomposites

This paper focuses on the analysis of drilling induced damage on biocomposites (woven fibers of cotton, flax and jute combined with polylactic acid, PLA, as the matrix). The main contribution of this work is the analysis of the influence of cutting parameters and drill geometry on fully biodegradable composites based on two different types of PLA and different fibers types. The damaged area was studied both at the hole entry and exit. Contrary to the behavior commonly observed when drilling conventional composites, delamination was negligible. The hole entry and exit damage were analyzed and quantified in terms of the fraying extension being the dominant. The damage extension was found to be dependent on the matrix, fiber type and drill geometry. The combination between cotton fiber and the small drill point angle showed the lowest level of damage. On the other hand, composite reinforced with flax fibers (those that exhibited the highest tensile strength) presented the greatest damage extension, increasing with the number of layers of the composite. The matrix based on polymer 10361D PLA, recommended for natural fibers because of the better interface cohesion, resulted in reduced fraying. Concerning the influence of cutting parameters, damage decreased when increasing the cutting speed and feed rate.

Parametric Study on the Manufacturing of Biocomposite Materials

This paper presents an analysis of the fabrication parameters that influence on the mechanical properties of biodegradable composites. Specimens were manufactured using film stacking and compression moulding process. The main analysed parameters were: constituent materials (fibres and matrix), heating temperature and pressure, thickness, fibre orientation and woven architecture. Two different polylactic acid (PLA) matrices, and four different woven fibres of Jute, Flax and Cotton were combined. Because of the parametric study, the influence of each parameter was analysed leading to an optimized manufacturing method. The results were analysed in terms of tensile strength and failure strain.