Machining FEM model of long fiber composites for aeronautical components

This work is focused on the study of orthogonal cutting of long fiber composites. A model based in finite element was developed. The mechanisms of chip formation of Glass and Carbon Fiber Reinforced Polymer (FRP) composites were analyzed. Significant differences were observed when comparing machining induced damage predicted with the model for both materials. While damage extended widely ahead the interface and beneath the tool tip in the case of GFRP, damage was located in a much smaller zone in the case CFRP. The fiber orientation influences both the mechanism of chip formation and the induced subsurface damage.The authors are indebted for the financial support of this work, to the Ministry of Science and Education of Spain (under Project DPI2008-06746). The authors also acknowledge to the CAMUC3 M for the financial support obtained for this work with the Project CCG08-UC3 M/DPI-4494.Publicad

Out-of-plane failure mechanisms in LFRP composite cutting

LFRP (Long Fiber Reinforced) composites are widely used in structural components for high responsibility applications in different industrial sectors. Composite components are manufactured near final shape, however several machining operations are commonly required to achieve dimensional and assembly specifications. Machining should be carefully carried out in order to avoid workpiece damage. Despite of the interest of numerical modeling to analyze in detail the phenomena involved during composite cut ting, there are only few works in the scientific literature dealing with this topic even in the simple case of orthogonal cutting. Out of plane failure can be accounted only if three dimensional modeling is per formed. However up to date numerical analysis of cutting found in scientific literature was focused in two dimensional approach. In this paper (2D) and three dimensional (3D) numerical modeling of orthog onal cutting of carbon LFRP composite are presented. The aim of the paper is to analyze the complex aspects involved during cutting, including out of plane failure.The authors are indebted for the financial support of this work, to the Ministry of Science and Innovation of Spain (under project DPI2008 06746)Publicad

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.This work was supported by Spanish Comisión Interministerial de Ciencia y Tecnología [project TRA2004 03960].Publicad

Influence of temperature on composite aeronautical structural bolted joints

15th International Conference on Composite Structures (ICCS/15), University of Porto, Porto, Portugal, 15-17 June 2009This work focuses on the analysis of temperature and bolt torque influence on aeronautical joint behaviour. A numerical model based on finite elements was developed. Results obtained from numerical simulations showed coupled influence of temperature combined with torque level on the jointPublicad

Monitoring temperature on machining processes is enhanced using optical fibers

An IR fiber-optic pyrometer measures temperatures above 250 C close to rotating components where other sensing techniques are unsuitableThis work has been sponsored by the Spanish Ministry of Economy and Competitiveness under grant TEC2012-37983-C03-02.Publicad

A heterogeneous orientation criterion for crack modelling in cortical bone using a phantom-node approach

Cortical bone can be considered as a heterogeneous composite at microscopic scale, composed of osteons that act as reinforcement fibres embedded in interstitial matrix. Cement lines constitute the interface between osteons and matrix, and they often behave as the weakest links along which microcracks tend to propagate. However, current simulations of crack growth using XFEM combined with usual orientation criteria as implemented in commercial codes do not capture this behaviour: they predict crack paths that do not follow the cement lines surrounding osteons. The reason is that the orientation criterion used in the implementation of XFEM does not take into account the heterogeneity of the material, leading to simulations that differ from experimental results. In this work, a crack orientation criterion for heterogeneous materials based on interface damage prediction in composites is proposed and a phantom node approach has been implemented to model crack propagation. The method has been validated by means of linear elastic fracture mechanics (LEFM) problems obtaining accurate results. The procedure is applied to different problems including several osteons with simplified geometry and an experimental test reported in the literature leading to satisfactory predictions of crack paths.The funding support received from the Spanish Ministry of Economy and Competitiveness and the FEDER operation program in the framework of the projects DPI2013-46641-R, DPI2017-89197-C2 and RTC-2015-3887-8 and also from the Generalitat Valenciana through the Programme PROMETEO 2016/007

Influence of tool geometry and numerical parameters when modeling orthogonal cutting of LFRP composites

The first objective of this paper is to analyze the influence of mesh size and shape in finite element modeling of composite cutting. Also the influence of the level of energy needed to reach complete breakage of the element is considered. The statement of this level of energy is crucial to simulate the material behavior. On the other hand geometrical characteristics of the tool have significant influence on machining processes. The second objective of the present work is to advance in the knowledge concerning tool geometry and its effect in composite cutting. A two-dimensional finite element model of orthogonal cutting has been developed and validated for Glass LFRP composite, comparing with experimental results presented in scientific literature. It was demonstrated that both numerical parameters and tool geometry influence the predicted chip morphology and machining induced damage.The authors are indebted for the financial support of this work, to the Ministry of Science and Innovation of Spain (under Project DPI2008 06746)Publicad

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.The authors acknowledge the financial support for the work to the Ministry of Economy and Competitiveness of Spain under the projects DPI2011-25999 and DPI2010-15123.Publicad

Temperature Measurement and Numerical Prediction in Machining Inconel 718

Thermal issues are critical when machining Ni-based superalloy components designed for high temperature applications. The low thermal conductivity and extreme strain hardening of this family of materials results in elevated temperatures around the cutting area. This elevated temperature could lead to machining-induced damage such as phase changes and residual stresses, resulting in reduced service life of the component. Measurement of temperature during machining is crucial in order to control the cutting process, avoiding workpiece damage. On the other hand, the development of predictive tools based on numerical models helps in the definition of machining processes and the obtainment of difficult to measure parameters such as the penetration of the heated layer. However, the validation of numerical models strongly depends on the accurate measurement of physical parameters such as temperature, ensuring the calibration of the model. This paper focuses on the measurement and prediction of temperature during the machining of Ni-based superalloys. The temperature sensor was based on a fiber-optic two-color pyrometer developed for localized temperature measurements in turning of Inconel 718. The sensor is capable of measuring temperature in the range of 250 to 1200 °C. Temperature evolution is recorded in a lathe at different feed rates and cutting speeds. Measurements were used to calibrate a simplified numerical model for prediction of temperature fields during turning.This work was supported by the Spanish Ministry of Economy and Competitiveness and FEDER program under grants TEC2015-63826-C3-2-R and DPI2014-56137-C2-2-R, and from Comunidad de Madrid under grant S2013/MIT-2790

Two-Color Pyrometer for Process Temperature Measurement During Machining

A fast fiber-optic two-color pyrometer operating on the optical communication bands is designed for temperature measurements in machining processes. Off-the-shelf low-loss fiber-optic demultiplexers and optoelectronics equipment are used in order to obtain a cost-effective sensing solution while reducing both the temperature measurement error and the minimum measurable temperature. The system is capable of measuring highly localized temperatures without using collimation lens. The designed pyrom-eter allows measuring temperature in the range from 300 to 650 °C, achieving a full-scale temperature error as low as 4%. Factors in-fluencing the temperature measurements are studied in order to identify the sensor limitations, such as a possible damage on the end of the optical fiber, the spectral loss attenuation and responsivity, or the distance between the fiber end and the target. Finally, this pyrometer is applied in a turning process, using a fiber-optic sensor embedded on a standard tool holder. Temperature measurements on the Inconel 718 are reported showing a good agreement with the simulations.This work was supported by the Spanish Ministry of Economía y Competitividad under Grants TEC2012-37983-C03-02, P2013/MIT-2790, and DPI2014-56137-C2-2-R.Publicad