Application of kinetic pyrolysis models to the analysis of flax chipboards under fire

This study presents a three-dimensional finite element model to describe the thermomechanical behaviour of flax chipboards under fire conditions. The model is based on kinetic models considering the thermal degradation during the pyrolysis phase and the evolution of the physico-mechanical properties as functions of temperature. The numerical model is integrated into Abaqus via user subroutines (Umat and Umatht) and applied to the analysis of the fire behaviour of panels made of flax chipboards. Thermogravimetric tests are performed on flax particles to serve for the identification of the kinetic parameters of the pyrolysis models. Once these kinetic parameters are determined, they are integrated into a complete numerical model to simulate the behaviour under fire of flax chipboards on small and large scales. The obtained trends in the predicted values indicate good agreements when compared to the measured values. The simulations show that the numerical model is capable of accurately modelling the thermomechanical transfers taking place within the material during exposure to fire

Fatigue analysis-based numerical design of stamping tools made of cast iron

This work concerns stress and fatigue analysis of stamping tools made of cast iron with an essentially pearlitic matrix and containing foundry defects. Our approach consists at first, in coupling the stamping numerical processing simulations and structure analysis in order to improve the tool stiffness geometry for minimizing the stress state and optimizing their fatigue lifetime. The method consists in simulating the stamping process by considering the tool as a perfect rigid body. The estimated contact pressure is then used as boundary condition for FEM structure loading analysis of the tool. The result of this analysis is compared with the critical stress limit depending on the automotive model. The acceptance of this test allows calculating the fatigue lifetime of the critical zone by using the S–N curve of corresponding load ratio. If the prescribed tool life requirements are not satisfied, then the critical region of the tool is redesigned and the whole simulation procedures are reactivated. This method is applied for a cast iron EN-GJS-600-3. The stress-failure (S–N) curves for this material is determined at room temperature under push pull loading with different load ratios R0σmin/σmax0−2, R0−1 and R00.1. The effects of the foundry defects are determined by SEM observations of crack initiation sites. Their presence in tested specimens is associated with a reduction of fatigue lifetime by a factor of 2. However, the effect of the load ratio is more important

Review of state of the art of dowel laminated timber members and densified wood materials as sustainable engineered wood products for construction and building applications

Copyright © 2019 The Authors. Engineered Wood Products (EWPs) are increasingly being used as construction and building materials. However, the predominant use of petroleum-based adhesives in EWPs contributes to the release of toxic gases (e.g. Volatile Organic Compounds (VOCs) and formaldehyde) which are harmful to the environment. Also, the use of adhesives in EWPs affects their end-of-life disposal, reusability and recyclability. This paper focusses on dowel laminated timber members and densified wood materials, which are adhesive free and sustainable alternatives to commonly used EWPs (e.g. glulam and CLT). The improved mechanical properties and tight fitting due to spring-back of densified wood support their use as sustainable alternatives to hardwood fasteners to overcome their disadvantages such as loss of stiffness over time and dimensional instability. This approach would also contribute to the uptake of dowel laminated timber members and densified wood materials for more diverse and advanced structural applications and subsequently yield both environmental and economic benefits.Interreg North-West Europe (NWE) funded by the European Regional Development Fund (ERDF) supporting the project (Towards Adhesive Free Timber Buildings (AFTB) - 348)

Towards the three-dimensional FE analysis of rapid prototyping tools for sheet metal stamping process

International audienceFor low volume production or for rapid prototyping, sheet metal stamping tools can be made by an assemblage of steel sheets or layers and joined by several techniques (such as screws, bolts, brazing, adhesive). However, an important problem in the design and the production of such tools is their mechanical behaviour, in particular the strength of joining techniques which is crucial in the aim of achieving the high required reliability of tools. If tools mechanical behaviour can be mastered and accurately predicted this can increase the tools life duration and be more beneficial for the manufacturing community. In order to properly predict the mechanical behaviour of tools, numerical simulation of stamping taking into account, elastic deformation of tools within a coupled FE analysis is needed. However, simulation results show that the effort and computational times required for such a coupled simulation, in particular in a general three-dimensional (3D) case, could be prohibitive and unrealistic. In this paper, the authors proposed and developed a numerical procedure in two steps, which has the advantage of decoupling the simulation of the blank forming and the stress analysis of the elastic tools. Numerical application is presented for a layered stamping punch, based on the Stratoconceptions rapid prototyping process, joined by screws in addition to an epoxy adhesive. The results are focussed on the screws behaviour, showing the potential interest of the developed procedure and numerical modelling technologies in designing layered tools joined by screws

Experimental and numerical analysis of CFRP-strengthened finger-jointed timber beams

International audienceExperimental and finite element (FE) studies of bending behaviour of finger-jointed timber (Spruce) beams reinforced with CFRP material were performed. Four-point bending tests with distinct reinforcement configurations were proposed in order to determine stiffness, ductility and strength values of strengthened finger-jointed timber beams. The experimental results obtained under flexure showed that the external bonding of CFRP increased the load-bearing capacity of finger-jointed Spruce timber beams. The numerical results presented here were based on the Cohesive Zone Model (CZM) available in Abaqus code, allowing the description of the progressive failure mode of the finger-jointed timber beams under flexural load. The FE models took the different material constitutive laws (wood, CFRP and adhesive) into account, including the bond-slip actions between finger-joints and CFRP-timber interface. The results in terms of load-mid span deflection and failure modes obtained experimentally and numerically were compared. Once the FE simulations were calibrated, the differences between experimental and predicted ultimate loads were around 4.5% only. A good agreement was therefore found, proving the relevance of the presented FE models to predict the load-bearing capacity and to capture the failure mode of CFRP-strengthened finger-jointed Spruce timber beams in bending

Towards experimental and numerical assessment of the vibrational serviceability comfort of adhesive free laminated timber beams and CLT panels assembled using compressed wood dowels

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A methodology for the 3D stress analysis and the design of layered sheet metal forming tools joined by screws

International audienceIn sheet metal forming industry, several experimental trials have been carried out successfully in the last 10 years, to demonstrate the feasibility of layered forming tools, by various rapid prototyping techniques. Recently, a layered stamping punch, based on the Stratoconception (R) process, was produced in a Craft European project Fastool and used successfully to produce some parts. The layered punch was joined using several screws in addition to an epoxy adhesive. Numerical simulation softwares allowing for 3D stress analysis of the layered tools are needed to evaluate their deformation and the various solutions of an assembly system. In this context, the authors proposed and developed a simplified numerical procedure, based on two steps, for the 3D stress analysis of deformable tools (layered or not). In addition, an optimization procedure, based on design of experiments and response surface method, has been established in order to optimize the screw positions, which are crucial in the aim of achieving the required high strength and life duration of the assembly technique by screws. The results show the feasibility of the developed procedure in the context of industrial applications, the potential interest of the optimization of the screw positions is also outlined

Non-linear finite element modelling of the structural behaviour of screwed timber-to-concrete composite connections

International audienceThis paper discusses a numerical approach, based on beam-to-solid modelling, for the simulation of the nonlinear structural behaviour of timber-to-concrete composite beams made with screws. The present contribution is an alternative to the detailed 3D modelling of the screws using solid elements and simplified approaches which use spring elements at each screw location. The screws were modelled using one-dimensional beam element, while the timber and concrete members were modelled, in detail, using 3D solid elements. To deal with the coupling between the common nodes, the 4-node beam element with only translational degrees of freedom (d.o.f.) per node, recently developed by the authors [1,2], has been extended to nonlinear analysis and employed to model the screws, since the existing 2-node beam element is obviously not fulfilled for screws in timber [2]. The effectiveness of the numerical model developed was verified experimentally showing several advantages by comparison to the existing models in the literature

A new approach to model nailed and screwed timber joints using the finite element method

International audienceThis paper presents a novel way to simulate the behaviour of nailed and screwed timber joints, using the finite element method. In order to avoid the detailed 3D modelling of nails (or screws) using solid elements, which is costly ineffective, the authors proposed and developed an approach based on beam-to-solid coupling where the nails (or screws) were modelled using one-dimensional beam element, while the assembled timber members were modelled using solid elements. To deal with the coupling between the degrees of freedom (d.o.f.) belonging to the screws and those belonging to the timber, the existing 2-node beam element has been modified involving in a 4-node beam element with only translational d.o.f. per node, leading in fact to a full compatibility with solid elements. Using the numerical approach developed, the linear elastic behaviour of a push-out shear test of a single shear timber-to-timber connection was successfully simulated