A thermoviscoplastic model with damage for simultaneous hot/cold forging analysis

A constitutive model is presented for simultaneous hot/cold forming processes of steels. The phenomenological material theory is based on an enhanced rheological model and accounts temperature dependently for nonlinear hardening, thermally activated recovery effects, an improved description of energy storage and dissipation during plastic deformations, and damage evolution as well. A thermomechanically consistent treatment of dissipative heating due to inelastic deformations, recovery processes and damage mechanisms is applied. The constitutive model is implemented into a commercial FE-code. The material parameters of the effective model response are identified for a low alloyed steel and validated by means of a simultaneous hot/cold forging process

On the Generalization of Uniaxial Thermoviscoplasticity with Damage to Finite Deformations Based on Enhanced Rheological Models

The enhanced concept of rheological models, as proposed in Br¨ocker and Matzenmiller (2013), is generalized systematically to finite deformations. The basic bodies are defined individually for large deformations, and a rheological network of thermoviscoplasticity is assembled, representing nonlinear isotropic and kinematic hardening as well as an improved description of energy storage in metal plasticity. The constitutive equations are deduced in an analogous procedure as for the uniaxial model in Br¨ocker and Matzenmiller (2013). Furthermore, damage evolution is additionally accounted for

Three-dimensional woven carbon fibre polymer composite beams and plates under ballistic impact

Clamped rectangular orthogonal 3D woven carbon composite beams under ballistic impact at a velocity range were investigated in order to understand the damage mechanisms within the material and the role of through-the-thickness (TTT) reinforcement. Experimental tests revealed three distinct categories of beam response: (i) low velocity impacts () which featured projectile rebound, with dominant matrix cracking and localised fibre fracture, (ii) medium velocity impact () which exhibited a stretch-deformation dominated failure mechanism, and (iii) higher velocity impacts () which resulted in projectile penetration, combined with longitudinal fibre fracture at the centre of the sample. Finite element (FE) simulations were conducted to understand the experimental outcomes, which showed sufficient fidelity and captured the three distinct beam response regimes. The presence of the TTT-reinforcement can suppress the inter-laminar matrix crack propagation and increase the material ballistic impact resistance for low velocity impact and high velocity impact. However, for medium velocity impact, the in-plane fibre fracture surface was found to be at the locations of TTT-reinforcement. This may suggest that the TTT-reinforcement may create weak points for the stretch-deformation dominated failure mechanism. The verified FE simulations were conducted to predict the multi-hit ballistic impact limit surfaces for the clamped circular 3D woven composite plates, and for the equivalent laminate composite without the presence of the TTT reinforcement. The numerical results suggested the presence of TTT reinforcement could improve the multi-hit ballistic resistance of the composite plates for multi-hit scenarios where the initial impact being 50% - 95% of the ballistic limit of the plates

Intraply fracture of fiber-reinforced composites: microscopic mechanisms and modeling

The fracture behavior parallel to the fibers of an E-glass/epoxy unidirectional laminate was studied by means of three-point tests on notched beams. Selected tests were carried out within a scanning electron microscope to ascertain the damage and fracture micromechanisms upon loading. The mechanical behavior of the notched beam was simulated within the framework of the embedded cell model, in which the actual composite microstructure was resolved in front of the notch tip. In addition, matrix and interface properties were independently measured in situ using a nanoindentor. The numerical simulations very accurately predicted the macroscopic response of the composite as well as the damage development and crack growth in front of the notch tip, demonstrating the ability of the embedded cell approach to simulate the fracture behavior of heterogeneous materials. Finally, this methodology was exploited to ascertain the influence of matrix and interface properties on the intraply toughness

A DEM model for visualising damage evolution and predicting failure envelope of composite laminae under biaxial loads

A two dimensional particle model based on the discrete element method (DEM) is developed for micromechanical modelling of fibre reinforced polymer (FRP) composite laminae under biaxial transverse loads. Random fibre distribution within a representative volume element (RVE) is considered for the micromechanical DEM simulations. In addition to predicting the stress-strain curves of the RVEs subjected to transverse compression and transverse shear stresses against the experimental testing results and other numerical modelling results, the DEM model is also able to capture the initiation and propagation of all micro damage events. Fibre distribution is found to more significantly influence the ultimate failure of composite laminae under transverse shear, while it has much less effect on the failure under transverse compression. The failure envelope of composite laminae under biaxial transverse compression and transverse shear is predicted and compared with Hashin and Puck failure criteria, showing a reasonable agreement. The predicted failure envelope is correlated with the damage evolution and the quantitative analysis of failure events, which improves the understanding of the failure mechanisms

Collapse of 3D orthogonal woven carbon fibre composites under in-plane tension/compression and out-of-plane bending composite structures

An experimental and numerical investigation was undertaken to characterise the collapse of 3D orthogonal woven carbon fibre composites during the load cases of in-plane tension, inplane compression and out-of-plane bending. Two different fibre architectures, varying only by the density of through-thickness reinforcement, were investigated. Cantilever beam tests were carried out to isolate two distinct collapse mechanisms, i.e. bending governed and shear governed deformation. A qualitative comparison was made with a similar UD-laminate material. 3D woven composites exhibited significantly reduced delamination. An investigation into the efficacy of an embedded element modelling strategy for in-plane tension, in-plane compression and out-of-plane bending load cases was undertaken. The predictions were generally in good agreement with the experimental measurements for the inplane and out-of-plane loading

Modelling low velocity impact induced damage in composite laminates

The paper presents recent progress on modelling low velocity impact induced damage in fibre reinforced composite laminates. It is important to understand the mechanisms of barely visible impact damage (BVID) and how it affects structural performance. To reduce labour intensive testing, the development of finite element (FE) techniques for simulating impact damage becomes essential and recent effort by the composites research community is reviewed in this work. The FE predicted damage initiation and propagation can be validated by Non Destructive Techniques (NDT) that gives confidence to the developed numerical damage models. A reliable damage simulation can assist the design process to optimise laminate configurations, reduce weight and improve performance of components and structures used in aircraft construction

Modelling low velocity impact induced damage in composite laminates

The paper presents recent progress on modelling low velocity impact induced damage in fibre reinforced composite laminates. It is important to understand the mechanisms of barely visible impact damage (BVID) and how it affects structural performance. To reduce labour intensive testing, the development of finite element (FE) techniques for simulating impact damage becomes essential and recent effort by the composites research community is reviewed in this work. The FE predicted damage initiation and propagation can be validated by Non Destructive Techniques (NDT) that gives confidence to the developed numerical damage models. A reliable damage simulation can assist the design process to optimise laminate configurations, reduce weight and improve performance of components and structures used in aircraft construction

A Thermodynamically-Based Mesh Objective Work Potential Theory for Predicting Intralaminar Progressive Damage and Failure in Fiber-Reinforced Laminates

A thermodynamically-based work potential theory for modeling progressive damage and failure in fiber-reinforced laminates is presented. The current, multiple-internal state variable (ISV) formulation, enhanced Schapery theory (EST), utilizes separate ISVs for modeling the effects of damage and failure. Damage is considered to be the effect of any structural changes in a material that manifest as pre-peak non-linearity in the stress versus strain response. Conversely, failure is taken to be the effect of the evolution of any mechanisms that results in post-peak strain softening. It is assumed that matrix microdamage is the dominant damage mechanism in continuous fiber-reinforced polymer matrix laminates, and its evolution is controlled with a single ISV. Three additional ISVs are introduced to account for failure due to mode I transverse cracking, mode II transverse cracking, and mode I axial failure. Typically, failure evolution (i.e., post-peak strain softening) results in pathologically mesh dependent solutions within a finite element method (FEM) setting. Therefore, consistent character element lengths are introduced into the formulation of the evolution of the three failure ISVs. Using the stationarity of the total work potential with respect to each ISV, a set of thermodynamically consistent evolution equations for the ISVs is derived. The theory is implemented into commercial FEM software. Objectivity of total energy dissipated during the failure process, with regards to refinements in the FEM mesh, is demonstrated. The model is also verified against experimental results from two laminated, T800/3900-2 panels containing a central notch and different fiber-orientation stacking sequences. Global load versus displacement, global load versus local strain gage data, and macroscopic failure paths obtained from the models are compared to the experiments