Papers by Keyword: Damage Evolution

Abstract: The various joints employed in high-pressure reinforced thermoplastic composite pipes (RTPs) face several challenges, including large outer diameters, complex traversal structures, and susceptibility to corrosion. To address these issues, this paper proposes a welding-reinforced joint structure and investigates its failure mechanism under tensile loading. Based on the 3D Hashin failure criterion, VUMAT subroutines were developed to model the exponential damage evolution of both unidirectional fiber-reinforced and woven composites. A three-dimensional finite element mode was established to perform dynamic analysis under tensile conditions, incorporating a cohesive zone model and VUMAT. The analysis results show that as tensile displacement increases, the bonding interface undergoes gradual debonding, with separation starting at the ends of the joint and propagating toward the middle. Once the interface is fully debonded, the high-density polyethylene (HDPE) in the welding region fails immediately. The maximum failure factors for both the RTP and the joint occur at the edges of the remaining bonding interface. his finding is consistent with the dynamic pattern of interface damage and failure.

Abstract: Currently, adhesive bonding has been increasingly used in various industrial applications such as in automobile lightweight structures for multi-material assembly. However, adhesive joints show a complex failure behavior. Their failure modes can be either adhesive failure, cohesive failure, or mixed mode failure depending on their interfacial strength and also the strength of adhesive layer which also varies with hydrostatic pressure. In this study, the failure of the adhesive joints with an epoxy-based adhesive bonded to metallic substrates are investigated numerically using FEA. The damage evolution model is implemented in the finite element model to predict the failure of adhesive joints. The adhesive strengths under different states of stress for a damage evolution model are characterized using the modified Arcan fixture which is specifically designed to study of hydrostatic pressure effect on an adhesive behavior. The validation of the failure model is carried out with the results of single lap shear test. A good agreement is finally found between FEA and experiments.

Abstract: Laminated composite structures are subjected to impact damage during maintenance and manufacturing operations and their life service. Driven by the necessity to value damage tolerance and durability of composite materials, an analysis of multi-hit impact is conducted to reproduce the real service conditions. Despite many studies in the literature investigated the properties of composites at low impact velocity, in contrast the behavior of the hybrid configuration, especially at repeated impacts, result still little known. This work presents an experimental and numerical study of the dynamic behavior at the repeated low-velocity impact of a carbon and glass fibers hybrid composite laminate.

Abstract: We report on an analytical model for damage description in adhesive butt joints. In themodel, the thin adhesive layer is replaced by a damaging bonding interface. The mechanical behaviorof the interface is described by a nonlinear and rate­dependent imperfect contact law. The law takesinto account both stress and displacement jumps, and it can describe both soft and hard adhesive layers.Unlike classic cohesive zone models, phenomenological in nature, the proposed contact law explicitlyaccounts for material and damage properties of the adhesive layer. A first comparison with literaturedata of adhesive butt joints loaded in torsion indicates that the model can successfully reproduce theirexperimental stress­strain response.

Abstract: 3D imaging techniques have an enormous potential to understand the microstructure, its evolution, and its link to mechanical, thermal, and transport properties. In this conference paper we report the use of a powerful, yet not so wide-spread, set of X-ray techniques based on refraction effects. X-ray refraction allows determining internal specific surface (surface per unit volume) in a non-destructive fashion, position and orientation sensitive, and with a nanometric detectability. We demonstrate showcases of ceramics and composite materials, where microstructural parameters could be achieved in a way unrivalled even by high-resolution techniques such as electron microscopy or computed tomography. We present in situ analysis of the damage evolution in an Al/Al₂O₃ metal matrix composite during tensile load and the identification of void formation (different kinds of defects, particularly unsintered powder hidden in pores, and small inhomogeneity’s like cracks) in Ti64 parts produced by selective laser melting using synchrotron X-ray refraction radiography and tomography.

Abstract: In this work, we present a model for the initiation and evolution of damage for a composite fibre-reinforced pipe used in the Oil & Gas industry, based on a commercially available pipe. A continuum damage mechanics model was employed to determine the initiation and evolution of damage. This model was implemented using finite element analysis to investigate the performance of the commercial composite pipe. Initially, the material properties were obtained from experimental data and fitting with static structural simulations. Then, FE simulations with damage were performed, considering three different boundary conditions: open, closed (pressure-vessel type) and fixed ends, the load considered was internal pressure. Results showed differences not only in the stress distribution but on the damage initiation and evolution along the geometry of the pipe. These differences in the damage initiation and propagation can be explained as the result of different axial-hoop stress ratio.

Abstract: Embodying the contemporary concern for eco-friendly mobility alternatives, solar vehicles have been developed and perfected in an exponential rate for the last two decades; powered by the supports from industry and research centres and the realization of world-class race competitions. Given the engineering complexity embraced by such state-of-the-art emergent technology, design challenges have been constantly arising for a successful and efficient vehicle architecture, mainly involved by the need for lightweight and resistant materials, which has been so forth supplied by composites. The application of such materials has been addressed both to decrease the overall weight of the vehicle, providing an enhanced energy efficiency, and for manufacturing structural parts granting high resistance and safety. Thus, emphasizing the importance of a proper knowledge on the behaviour of composites, this work aims at reviewing studies upon some static and dynamic mechanical properties, focusing on low-energy impact, damage evolution and failure characterization, with glances at sustainability; comparing composite materials with different fibre reinforcements and narrowing such analysis to actual known applications in solar cars.

Abstract: Structural aircraft components are often subjected to more than 108 loading cycles during their service life. Therefore the increasing use of carbon fiber reinforced polymers (CFRP) as primary lightweight structural materials leads to the demand of a precise knowledge of the fatigue behavior and the corresponding failure mechanisms in the very high cycle fatigue (VHCF) range. To realise fatigue investigations for more than 108 loading cycles in an economic reasonable time a novel ultrasonic fatigue testing facility (UTF) for cyclic three-point bending was developed and patented. To avoid critical internal heating due to viscoelastic damping and internal friction, the fatigue testing at 20 kHz is performed in resonance as well as in pulse-pause control resulting in an effective testing frequency of ~1 kHz and the capability of performing 109 loading cycles in less than twelve days. The fatigue behavior of carbon fiber twill 2/2 fabric reinforced polyphenylene sulfide (CF-PPS) and carbon fiber 4-H satin fabric reinforced epoxy resin (CF-EP) was investigated. To study the induced fatigue damage of CF-PPS and CF-EP in the VHCF regime in detail, the fatigue mechanisms and damage development were characterized by light optical and SEM investigations during interruptions of constant amplitude tests (CAT). Lifetime-oriented investigations showed a significant decrease of the bearable stress amplitudes of CF-PPS and CFEP in the range between 106 to 109 loading cycles. The ultrasonically fatigued thermoset matrix composite showed a significantly different VHCF behavior in comparison to the investigated thermoplastic matrix composite: No fiber-matrix debonding or transversal cracks were present on the specimen edges, but a sudden specimen failure along with carbon fiber breakage have been observed. The fatigue shear strength at 109 cycles for CF-PPS could be determined to τa, 13 = 4.2 MPa and to τa, 13 = 15.8 MPa for the thermoset material CF-EP.

Abstract: In order to reduce fuel consumption due to environmental aspects, weight of automotive components has to be reduced. Fibre reinforced polymers have high potential to contribute to this aim as they feature a high ratio of stiffness to weight. The direct processing route for long fibre reinforced polymers is a potential process for the net shape series production of automotive parts. To retain safety and comfort, the material properties of polymers processed in such a way have to be investi-gated thoroughly implementing a deeper understanding of elastic response and damage mechanisms. This work deals with glass fibre reinforced polypropylene manufactured by a direct LFT processing route (D-LFT). After introducing basic properties, studies to determine damage evolution are presented. In this regard, the decrease of stiffness with increasing strain was analyzed using tensile tests featuring loading-unloading cycles. The materials properties have been correlated to fibre orientation measurements from X-ray computed tomography. The stiffness decrease is compared to stiffness measurements carried out by ultrasonic phase spectroscopy (UPS) tests, carried out on juvenile, undamaged specimens. This method is used in this study for the first time to describe the elastic properties of long fibre reinforced thermoplastics.

Abstract: This work is concerned with the development of a new process map for wire drawing of pearlitic steel considering damage evolution. In this study, a ductile damage is defined as a porosity or void volume fraction and the porosity evolution model proposed by Lee and Dawson is adopted. Dilatational plastic deformation due to growth of micro voids is also considered. Correspondingly, an Eulerian finite element analysis coupled with damage evolution model is utilized in order to reflect the effects of dilatational plasticity due to growth of micro voids. Also, the accumulated damage in wire drawing could be evaluated. Finite element simulation for wire drawing of pearlitic steel are performed for various process conditions such as a half die angle and an area reduction ratio. Especially, the effects of process parameters on the deformation characteristic as well as damage evolution in wire drawing are carefully examined. Finally, a new process map is presented in terms of a half die angle and an area reduction ratio, which can identify the successful process conditions for wire drawing of pearlitic steel. Thus, it would be expected that this process map will help an engineer for the design of wire drawing of pearlitic steel.