Fast simulation of 3D elastic response for wheel–rail contact loading using Proper Generalized Decomposition

To increase computational efficiency, we adopt Proper Generalized Decomposition (PGD) to solve a reduced-order problem of the displacement field for a three-dimensional rail head exposed to different contact scenarios. The three-dimensional solid rail head is modeled as a two-dimensional cross-section, with the coordinate along the rail being treated as a parameter in the PGD approximation. A novel feature is that this allows us to solve the full three-dimensional model with a nearly two-dimensional computational effort. Additionally, we incorporate the distributed contact load predicted from dynamic vehicle-track simulations as extra coordinates in the PGD formulation, using a semi-Hertzian contact model. The problem is formulated in two ways; one general ansatz which considers the treatment of numerous parameters, some of which exhibit a linear influence, and a linear ansatz where multiple PGD solutions are solved for. In particular, situations where certain parameters become invariant are handled. We assess the accuracy and efficiency of the proposed strategy through a series of verification examples. It is shown that the PGD solution converges towards the FE solution with reduced computational cost. Furthermore, solving for the PGD approximation based on load parameterization in an offline stage allows expedient handling of the wheel-rail contact problem online

Compressive failure and kink-band formation modeling

To increase the use of polymeric structural composites, a major issue is to properly account for intra-laminar failure mechanisms, such as fiber kinking induced under compression. We propose a new continuum damage model that can predict the fiber kinking response at the ply level. The model is based on a previous structure tensor-based model for the response of UD-plies. A novel feature is that the compressive UD-ply response at the macroscale includes the effect of the fiber misalignment shaped as a kink-band that is resolved at the sub-scale. Concepts of computational homogenization are used to include the fiber-shear of the kink-band at the sub-scale. The model calibration is adapted to account for either kink-band formation or shear-splitting depending on the off-axis loading. Finally, the model is validated at the laminate level against experimental data for OHC-tests available in the literature. A good agreement is found for predicted strength values and observed fracture patterns of the laminates. The size effect experienced when different hole sizes are tested is also addressed

A preform deformation and resin flow coupled model including the cure kinetics and chemo-rheology for the VARTM process

The present paper deals with preform deformation and resin flow coupled to cure kinetics and chemo-rheology for the VARTM process. By monitoring the coupled resin infusion and curing steps through temperature control, our primary aim is to reduce the cycle time of the process. The analysis is based on the two-phase porous media flow and the preform deformation extended with cure kinetics and heat transfer. A novel feature is the consideration of temperature and preform deformation coupled to resin viscosity and permeability in the VARTM process. To tackle this problem, we extend the porous media framework with the heat transfer and chemical reaction, involving additional convection terms to describe the proper interactions with the resin flow. Shell kinematics is applied to thin-walled preforms, which significantly reduces the problem size. The proposed finite element discretized system of coupled models is solved in a staggered way to handle the partially saturated flow front under non-isothermal conditions efficiently. From the numerical example, we conclude that the cycle time of the VARTM infusion process can be shortened over 68%with the proper temperature control. Moreover, the proposed framework can be applied to optimize the processing parameters and check the compatibility of a resin system for a given infusion task

Gradient-enhanced damage growth modelling of ductile fracture

We present a gradient enhanced damage model for ductile fracture modeling, describing the degraded material response coupled to temperature. Continuum thermodynamics is used to represent components of the energy dissipation as induced by the effective material response, thermal effects and damage evolution. As prototype for the effective material serves the viscoplastic Johnson-Cook constitutive model. The continuum damage evolution of Lemaitre type is focusing the degradation of the shear response eventually leading to ductile shear failure. A novel feature of the paper is the damage driving dissipation rate, allowing for elastic and plastic components separated by a global damage threshold for accumulation of inelastic damage driving energy. In the application to a dynamic split-Hopkinson test and two quasi-static tensile tests, the gradient damage model is compared to the corresponding local model. For isothermal conditions, the examples show that both damage models exhibit mesh convergent behavior when using the global damage threshold

Modeling and Experimental Validation of the VARTM Process for Thin-Walled Preforms

In this paper, recent shell model is advanced towards the calibration and validation of the Vacuum-assisted Resin Transfer Molding (VARTM) process in a novel way. The model solves the nonlinear and strongly coupled resin flow and preform deformation when the 3-D flow and stress problem is simplified to a corresponding 2-D problem. In this way, the computational efficiency is enhanced dramatically, which allows for simulations of the VARTM process of large scale thin-walled structures. The main novelty is that the assumptions of the neglected through-thickness flow and the restricted preform deformation along the normal of preform surface suffice well for the thin-walled VARTM process. The model shows excellent agreement with the VARTM process experiment. With good accuracy and high computational efficiency, the shell model provides an insight into the simulation-based optimization of the VARTM process. It can be applied to either determine locations of the gate and vents or optimize process parameters to reduce the deformation

A thermomechanically motivated approach for identification of flow stress properties in metal cutting

The paper presents a novel thermomechanically coupled distributed primary deformation zone model to assist the inverse identification of Johnson-Cook material parameters to be used for machining simulations. A special feature of the enhanced model is that the assumed stress field is temperature-dependent, where the thermomechanical coupling governs the stress and temperature distributions across the primary shear zone to describe the thermal softening effect. By using stress, strain, strain rate, and temperature distributions from the thermomechanically enhanced model, Johnson-Cook material parameters are calibrated for orthogonal cutting tests of C38, 42CrMo4, and AA6082 materials where continuous chip formation prevails. The performance of the parameters is compared with that of a wider set of cutting tests using finite element simulations. The results show that the thermomechanically motivated model yields closer results to experiments in terms of cutting force and chip thickness (9% and 34% difference, respectively) compared with the original thermally uncoupled model (47% and 92% difference, respectively). Identification of the material parameters by this method focuses directly on the orthogonal cutting test and it does not require many experiments or simulations. In fact, the proposed methodology is computationally robust and cost-efficient which makes it preferable compared with other methods which are more accurate but highly time-consuming

A micromechanics based model for rate dependent compression loaded unidirectional composites

Strain-rate effects in a unidirectional non-crimp fabric carbon/epoxy composite are addressed.\ua0To allow for kink-band formation including strain-rate\ua0 effects and damage in such composites, the paper advances a recent model focused on compression loading at small off-axis angles.\ua0The model is based on computational \textit{homogenization} with a subscale represented by matrix and fibre constituents at finite deformation.\ua0The fibre constituent is assumed to be elastic transversely isotropic and the matrix is viscoelastic--viscoplastic with damage degradation.\ua0Novel model improvements of special importance to small off-axis loading relate to the \textit{isostress} formulation of the homogenized response in transverse shear.\ua0In this context, an enhanced homogenized elastic response is proposed based on Halpin--Tsai corrections to account for the nonuniform stress distribution on the microscale.\ua0The model captures the strongly rate sensitive kink-band formation due to localized matrix shearing and fibre rotation, confirming the experimentally observed increase in compressive strength for high strain rates

Towards an accurate estimation of heat flux distribution in metal cutting by machine learning

This study presents a machine learning-based approach for inverse identification of heat flux distribution on the rake face of the cutting tools in machining. This approach includes temperature measurements from thermocouples embedded in the tool and heat transfer finite element (FE) simulations to create the data required to train the ML model. The identified heat flux distribution is compared with the distribution from FE machining simulations for validation. The results show a clear potential to estimate the heat flux distribution in machining more efficiently by using an ML-based inverse approach