Hybrid titanium-CFRP laminates for high-performance bolted joints

This paper presents an experimental and numerical investigation of the mechanical response of bolted joints manufactured using new hybrid composite laminates based on the substitution of CFRP plies with titanium plies. The local hybridization of the material is proposed to increase the efficiency of the bolted joints in CFRP structures. Two modeling strategies, based on non-linear finite element methods, are proposed for the analysis of the bolt-bearing and transition regions of the hybrid laminates. The bolt-bearing region is simulated using a three-dimensional finite element model that predicts ply failure mechanisms, whereas the free-edge of the transition region is simulated using plane stress and cohesive elements. The numerical and experimental results indicate that the use of hybrid composites can drastically increase the strength of CFRP bolted joints and therefore increase the efficiency of this type of connection. In addition, the numerical models proposed are able to predict the failure mechanisms and the strength of hybrid composite laminates with a good accuracy

Transient Finite Element Computations on a Variable Transputer System

A parallel program to analyze transient finite element problems was written and implemented on a system of transputer processors. The program uses the explicit time integration algorithm which eliminates the need for equation solving, making it more suitable for parallel computations. An interprocessor communication scheme was developed for arbitrary two dimensional grid processor configurations. Several 3-D problems were analyzed on a system with a small number of processors

Machining induced damage in orthogonal cutting of UD composites : FEA based assessment of Hashin and Puck criteria

FE models offer a promising virtual alternative to study machining responses of composites, thereby allowing an informed selection of favorable cutting parameters. Appropriate mathematical schemes are needed to predict damage initiation in fibrous composites; Hashin and Puck failure criteria are the most commonly used for this purpose. This work focusses on the assessment of these criteria to predict ply-level damage in orthogonal cutting of unidirectional composites. A novel algorithm accounting for strain-softening after damage initiation is also proposed. Efficacy of the developed FE model is shown by simulating effects of the cutter tool on the damage of underlying workpiece

Progressive damage modeling of synthetic fiber polymer composites under ballistic impact

Composite structures offer many advantages compared to conventional materials, especially where high strength and stiffness-to-weight ratio are concerned [1]. Thus composites have been used widely in many applications such as marine compo-nents, bicycle parts, petrochemicals, and protective gadgets. However, they are rela-tively sensitive to brittle behavior when loaded under static or fatigue conditions, which leads to damage and loss of stiffness

Calculation of the critical energy release rate Gc of the cement line in cortical bone combining experimental tests and finite element models

[EN] In this work, a procedure is proposed to estimate the critical energy release rate Gc of the so-called cement line in cortical bone tissue. Due to the difficulty of direct experimental estimations, relevant elastic and toughness material properties at bone microscale have been inferred by correlating experimental tests and finite element simulations. In particular, three-point bending tests of ovine cortical bone samples have been performed and modeled by finite elements. The initiation and growth of microcracks in the tested samples are simulated through finite elements using a damage model based on a maximum principal strain criterion, showing a good correlation with the experimental results. It is observed that microcracks evolve mainly along the cement lines and through the interstitial material but without crossing osteons. The numerical model allows the calculation of the cement line critical energy release rate Gc by approximating its definition by finite differences. This way, it is possible to estimate this property poorly documented in the literature.The authors wish to thank the Ministerio de Economia y Competitividad for the support received in the framework of the project DPI2013-46641-R and to the Generalitat Valenciana, Programme PROMETEO 2016/007. The authors also thank Dr. Jose Luis Peris, from Instituto de Biomecanica de Valencia (IBV) and Carlos Tudela Desantes for their collaboration within the context of the project.Giner Maravilla, E.; Belda, R.; Arango-Villegas, C.; Vercher Martínez, A.; Tarancón Caro, JE.; Fuenmayor Fernández, FJ. (2017). Calculation of the critical energy release rate Gc of the cement line in cortical bone combining experimental tests and finite element models. Engineering Fracture Mechanics. 184:168-182. https://doi.org/10.1016/j.engfracmech.2017.08.026S16818218

Simulating damage onset and evolution in fully bio-resorbable composite under three-point bending

This paper presents a strain-based damage model to predict the stress-strain relationship and investigate the damage onset and evolution of the fibre and matrix of a fully bio-resorbable phosphate glass fibre reinforced composite under three-point bending. The flexural properties of the composite are crucial, particularly when it is employed as implant for long bone fracture. In the model, the 3D case of the strain and stress was used and the response of the undamaged material was assumed to be linearly elastic. The onset of damage was indicated by two damage variables for the fibre and matrix, respectively. The damage evolution law was based on the damage variable and the facture energy of the fibre and matrix, individually. A finite element (FE) model was created to implement the constitutive model and conduct numerical tests. An auto-adaptive algorithm is integrated in the FE model to improve the convergence. The FE model was capable of predicting the flexural modulus with around 3% relative error, and the flexural strength within 2% relative error in comparison with the experimental data. The numerical indices showed that the top surface of the sample was the most vulnerable under three-point bending. It was also found that the damage initiated in the fibre, was the primary driver for composite failure under three-point bending

Watermarking analysis for digital images

praca magistersk