Experimental study of gas diffusion layers nonlinear orthotropic behavior

One of the most important components of PEMFC is the gas diffusion layer (GDL), owing to its key role in the reactant diffusion, water management, thermal and electron conductivity. Therefore, the GDL must have an optimal stiffness to ensure these transport functions during numerous hydrothermal cycles. The understanding of its behavior is still a remaining issue. Its orthotropic mechanical behavior requires a series of mechanical characterizations in the plane of the fibers and out of plane. In addition, there are different manufacturing processes for GDL in sheet or roll form to optimize its functional properties. A macro porous layer (MPL) or different PTFE contents might be added by different manufacturers to optimize its performance. In this study, we have performed several mechanical tests differentiating between in plane and out of plane properties in order to characterize different GDLs available on the market. All of the experimental work has been done in the machine (MD) and cross machine direction (CD) according to the fiber orientation. The different GDL types were then classified into categories presenting similar mechanical response.

Modeling and numerical simulation of the dynamic behavior of magneto-electro-elastic multilayer plates based on a Winkler-Pasternak elastic foundation

This work presents the effect of the elastic foundation and the viscoelastic interface on the dynamic behavior of laminated magneto-electro-elastic rectangular plates with simply supported boundary conditions using the state space method in Laplace domain. The Kelvin-Voigt model is used to take into accounted the viscoelastic interface effects in this domain. The final solution is transferred to the time domain by the Fourier inversion method. The dynamic responses of 3D displacements, stresses, and electric and magnetic displacements are analyzed with respect to the thickness direction and the orthotropic behavior under harmonic stress. A variant of the numerical tests shown the effect of the Winkler-Pasternak elastic foundation on a magneto-electro-elastic rectangular plates dynamic behavior and may contribute to optimize the design and the manufacturing of these materials.

Numerical simulation of Effect of Contact Pressure on Gas Diffusion Layers deformation of a PEM Fuel Cell

In this study, a two-dimensional, Finite Element model has been implemented based numerical modeling simulations to predict mechanical behavior of a representative unit of fuel cell stack deformation under three levels of contact pressure between GDL and bipolar plate assuming that the GDL deformation as a combination of elastic deformation and fibers slippage. The intrusion of the GDL into the channel was estimated. Indeed, with orthotropic behavior of the GDL, the proposed nonlinear orthotropic model converges towards the models of the literature as a function of the contact pressure level between the bipolar plate and the GDL (Gas Diffusion Layers).

Experimental characterization of composites to support an orthotropic plasticity material model

Test procedures for characterizing the orthotropic behavior of a unidirectional composite at room temperature and quasi-static loading conditions are developed and discussed. The resulting data consisting of 12 stress–strain curves and associated material parameters are used in a newly developed material model—an orthotropic elasto-plastic constitutive model that is driven by tabulated stress–strain curves and other material properties that allow for the elastic and inelastic deformation model to be combined with damage and failure models. A unidirectional composite—T800/F3900, commonly used in the aerospace industry, is used to illustrate how the experimental procedures are developed and used. The generated data are then used to model a dynamic impact test. Results show that the developed framework implemented into a special version of LS-DYNA yields reasonably accurate predictions of the structural behavior.

Out-of-Plane Mechanical Property Test on Titanium Honeycomb Cores

As a typical cellular solid, the honeycomb core shows an orthotropic behavior in its mechanical properties. Engineering analysis often adopts a homogeneity assumption that honeycomb core is equivalent to an anisotropic continuum. Currently available cellular solid model cannot predict the physical properties of titanium honeycomb core with acceptable accuracy. Therefore, mechanical test must be carried out to obtain the mechanical properties of metallic honeycomb structures. This paper introduces the work on flatwise compression test and out-of-plane shear test on titanium honeycomb core structures in accordance to ASTM C 365-03and ASTM C 273-00. The out-of-plane stiffness and strength for titanium honeycomb cores with incircle diameter of 4.8mm and wall thickness of 0.05mm were obtained.

Finite Element Modeling and Analysis of Orthotropic Butt Welds

Butt welds with orthotropic behavior are widely applied in mechanical and structural designs. Since welds cannot always be perfect in practice, it is important to understand the weld’s stress behavior under different imperfect geometries. In this paper research has been performed to investigate the relationship between stress intensity factors and change of geometry of orthotropic butt welds. Finite element methods were applied to simulate weld geometries. The simulation was performed using ANSYS software assuming two beams are welded together with a discontinuity at the bottom of the weld. The combined beams and the butt weld are then considered to be one piece of glued structure. The discontinuity in the structure is used to model a crack and lack of weld penetration. By changing three important factors of the weld geometry under uniform axial static loads, the trend of stress intensity factor behavior versus change of geometry has been investigated. Both single and double sided butt welds were considered in this paper. The results of this investigation will be a helpful tool for design engineers in deciding the best weld geometry in applications.

INVESTIGATING THE EFFECT OF THE ORTHOTROPIC PROPERTY OF PIEZOELECTRIC PVDF

The applications of the piezoelectric Polyvinylidene Fluoride, PVDF, integrated with the beams, plates, and membranes, performing as sensor, actuator or combination have been received considerable attention in the recent years. However, not much work has been reported on the influence of the PVDF’s orthotropic behavior, particularly the effect of the orientation of the PVDF film in the host structure, on the performance of the system. In the present study, the effect of the piezoelectric PVDF film orientation on the output voltage, the actuation force, and the dynamic response of the integrated structures has been studied using the finite element method. In the sensory mode, the difference between the output voltages obtained from the biaxial piezoelectric PVDF film and uniaxial one, when the orientation of the film varies from 0 to 90 degree, is investigated. In each case the proportion contributions of the involved piezoelectric coefficients including d31, d32 and are studied. Alternatively, in the actuation mode, the effect of orthotropic behavior of the actuator on the nodal displacements has been taken into consideration. The influence of the material orthotropic property of the transducer on the free undamped response of the system is also investigated. Moreover an effective Young’s modulus and effective Poisson ratio for the uniaxial PVDF film has been introduced using an optimization procedure to minimize the error caused by isotropic assumption of uniaxial PVDF film.

Validation of a New Aluminum Honeycomb Constitutive Model for Impact Analyses

A new constitutive model for large deformation of aluminum honeycomb has been developed. This model has 6 yield surfaces that are coupled to account for the orthotropic behavior of the cellular honeycomb being crushed on-axis and off-axis. Model parameters have been identified to fit uniaxial and biaxial crush test data for high density (38 lb/ft3) aluminum honeycomb. The honeycomb crush model has been implemented in the transient dynamic Presto finite element code for impact simulations. Simulations of calibration and validation experiments will be shown with model predictions compared with test data. Also, the honeycomb model's predictions will be compared with the older Orthotropic Rate Model predictions.

A Bimodular Second-Order Orthotropic Stress Constitutive Equation for Cartilage

The design of tissue-engineered constructs grown in vitro is a promising treatment strategy for degenerated cartilaginous tissues. Cartilaginous tissues such as articular cartilage and the annulus fibrosus are collagen fiber-reinforced composites that exhibit orthotropic behavior and highly asymmetric tensile-compressive responses. They also experience finite deformations in vivo. Successful integration with surrounding tissue upon implantation likely will require cartilage constructs to have similar structural and functional properties as native tissue. Reliable stress constitutive equations that accurately characterize the tissue’s mechanical properties must be developed to achieve this aim. Recent studies have successfully implemented bimodular theories for infinitesimal strains (Soltz et al., 2000; Wang et al., 2003); those models were based on the theory of Curnier et al. (1995).