Semi-crystalline polymers is an important group of materials that is used in a vast array of products. In this study, the rate-dependent properties of high-density polyethylene (HDPE) are ...investigated, both experimentally and theoretically. Experimental compression testing of a three-dimensional HDPE structure is performed and analysed numerically by use of the finite element method. In addition, an Eulerian constitutive material model for isotropic, semi-crystalline polymers is proposed. The model is able to account for such essential phenomena as strain-rate dependence, work hardening, pressure-dependence of inelastic deformations, and damage. The proposed material model was implemented in Abaqus as a VUMAT, which is an explicit implementation. The material model was calibrated by use of uniaxial tensile tests performed on HDPE dog-bone shaped samples, and the model was further explored by applying the VUMAT implementation to the compression tests of the HDPE structure. The simulation model was able to reproduce the experimental results well, both the uniaxial tests and the compression tests. In particular, the friction present in the compression tests seems to play an important role in determining the buckling mode of the structure.
•Experiments on high-density polyethylene: compression testing of a 3D structure.•Modelling of rate-dependent inelasticity and damage of semi-crystalline polymers at finite strains using an Eulerian formulation.•Analyses of rate-dependent buckling of the 3D structure.
The phase-field model for fractures regularizes crack diffusion using a length-scale parameter. The displacement fields and the phase-field in a coupled system can be solved as either fully coupled ...“monolithic” or sequentially coupled “staggered” fields. In this paper, we employ the commercial finite-element software Abaqus to solve the monolithic and staggered phase-field models using a user-defined element (UEL) and user-defined material (UMAT/VUMAT) subroutines in two- and three-dimensions for quasi-static and dynamic fractures. We present the implementation procedures for both strategies, and make a detailed comparison using different applications. By comparing the phase-field model as a diffusive crack model and the extended finite-element method (XFEM) as a discrete crack model, we obtain good agreement. We investigate the influence of the model-regularization parameter based on experimental results. We adopt the thread-parallel execution and mutexes of Abaqus solvers.
•Three different implementation strategies of phase-field damage models in Abaqus are addressed.•The sources codes and input files of all these three implementation schemes can be open ...accessed.•Representative examples validating the implementation strategies and source codes are presented.•The UEL subroutine together with the BFGS monolithic solver is of best numerical performances.•The UMAT subroutine is viable if the BFGS solver is available in coupled thermal–stress analyses.
Despite the versatility in modeling complex crack configurations, phase-field damage models for fracture usually count only on in-house codes, greatly restricting their potential applications. It is thus of vital importance to implement them in those commonly used commercial software packages like Abaqus. However, so far only the less robust Newton’s monolithic algorithm or the inefficient staggered solver has been considered. In this work, taking the unified phase-field damage theory (Wu, 2017) as the particular example, we present three distinct strategies of implementing phase-field damage models into Abaqus: (i) UMAT-Newton-M: a thermo-mechanically coupled user-defined material (UMAT) implementation of the modified Newton monolithic solver; (ii) UEL-Staggered: a novel user-defined element (UEL) implementation of the iterative staggered (alternate minimization) algorithm with dummy dofs; (iii) UEL-BFGS: a UEL implementation of the recently advocated BFGS quasi-Newton monolithic algorithm. The aforesaid implementation strategies are then validated against several representative benchmark problems of brittle fracture and quasi-brittle failure. It is found that, the UMAT-Newton-M implementation is the simplest but not robust enough, while the UEL-Staggered implementation is robust but extremely inefficient. Comparatively, in all cases the UEL-BFGS scheme is of the best numerical performance with lest iterations and sufficient robustness. For the sake of reproducibility of the presented numerical results and the promotion of phase-field damage models, the source codes (programmed in the free format syntax of FORTRAN90) are also provided and interested users can download them at https://github.com/jianyingwu/pfczm-abaqus.
Rolling in Directed Energy Deposition (DED) has shown promising improvements in build quality by providing compressive deformations. The rolling dynamics and associated boundary conditions are ...crucial for how these deformations impact the stress–strain profiles on the deposited part and substrate. This study investigates these impacts by developing a fully coupled dynamic-thermo-mechanical finite-element model in Abaqus for in-situ micro-rolling in DED. Single bead analyses have been done with a 2D heat flux moving ahead of the roller at a fixed offset. Two rolling boundary condition cases with varying friction at the roller-bead interface have been examined: (i) only translation defined with rotation calculated from roller-bead interaction and (ii) translation with a defined rotation corresponding to a no-slip condition. In the first case, analyses have shown that the surface stress–strain conditions and rolling load variation are susceptible to interfacial friction. With increasing friction, the surface conditions deteriorate and variations in rolling load increase. However, beyond the surface, the overall stress–strain profiles remain similar. The surface stress–strain profile and rolling load variation have been smoothened in the second case because of the defined rotation. Further, a comparison has been made between the results of dynamic-explicit analyses and static-implicit analyses to quantify the roller’s inertia effects. The stress–strain profiles predicted by both analyses have marginal differences but with 16 % over-prediction in rolling load by dynamic-explicit analyses. These results imply that the roller’s inertia marginally affects the deposited part’s stress–strain evolution but has a notable role in rolling load. Also, providing an external drive to the roller corresponding to the second case can effectively minimise the deteriorating effects of roller-bead interfacial friction.
•In-situ rolling dynamics are examined using explicit and implicit FE analyses.•Explicit analyses effectively captured rotational BCs and friction effects.•The roller’s inertia primarily impacted the prediction of rolling load.•Interfacial friction caused irregular surface stress–strain and rolling load.•External roller rotation eliminated the deteriorating effect of friction.
Bone is known to be a natural composite material with variation of mechanical properties depending on the location and orientation of specimen extracted. In this study, specimens of cortical bone ...extracted from three different locations and two different orientations were modelled in Abaqus by considering the material of cortical bone to be anisotropic in nature. The stress–strain curves of specimens for both transverse and longitudinal orientation for compressive and tensile testing has been plotted. It has been found from the curves that the specimen belonging to upper diaphysis has more values of mechanical properties in comparison to other specimen-type for both compressive and tensile testing. It has also been observed that the compressive test shows more value of yield stress, elastic modulus and ultimate stress in comparison to tensile test that is the cortical bone can wear more load in the compressive direction. The values of mechanical properties found to be more for longitudinal orientation in comparison to transverse orientation. The results obtained found a good relation with the existing literature.
An experimental test was conducted to analyze the Local Bond Stress (LBS) between Ultra-High-Performance Concrete (UHPC) and reinforcing steel bars. The test included 144 specimens based on RILEM ...standards, using pullout tests. Reinforcing steel bars of 16 mm and 18 mm in diameter, nano-silica contents from 0% to 6.5% by weight of cement, conventional and thermal curing methods, and the bond lengths and concrete covers of db, 2db and 3db were the research parameters in this study. Moreover, sixteen experimentally tested and 39 non-tested specimens were modeled using ABAQUS by taking into account additional parameters such as bond length and concrete cover of 4db, and bar diameters of 12, 14, 16, 18 and 20 mm. The resulting proposal was a comprehensive LBS equation to calculate the local bond stress between reinforcing steel bars and UHPC. A fair comparison between the results confirmed that the values obtained from the proposed LBS equation were logically in good agreement with the experimental and numerical results.
Brittle and ductile dynamic fracture in solids is a complex mechanical phenomenon which attracted much attention from both engineers and scientists due to its technological interests. Modeling cracks ...in dynamic cases based on a discontinuous description is difficult because it needs additional criteria for branching and widening. Due to the very short time scales and the spatial complexity of the dynamic problem, its experimental analysis is still very difficult. Therefore, researchers still have to rely on numerical simulations to find a deeper explanation for many observed phenomena. This study is set out to investigate the effect of plasticity on dynamic fracture propagation. On the other hand, the diffuse phase-field formulation makes it possible to initiate, propagate, arrest or even branch cracks while satisfying the basic principles of thermodynamics. An implicit, staggered elastoplastic version of the phase-field approach was implemented in the commercial finite element code Abaqus through the UEL option. By means of simple examples we show that localized ductile deformations first increase both resistance and toughness. Then, after a maximum value, the resistance starts to decrease with a significant increment in energy dissipation. By favoring shear deformation over tensile failure the fracture pattern changes. First the branching disappears, then the crack propagation angle changes and becomes a shear band. Finally, we observed the increment of the instantaneous dynamic stress intensity factor during the acceleration stage of the crack without introducing a rate dependent critical fracture energy. We explained this phenomenon with the increasing roughness of the fracture surface.
•Ductile dynamic phase-field algorithm is implemented in open-source Abaqus code.•Plasticity increases both resistance and toughness.•Dynamic stress intensity factor increases without rate dependent energy release rate.
•Numerical simulations of flood-induced scour around the piers of masonry bridges.•Failure mechanism simulation of an Italian bridge after the flood of December 2013.•Operational Modal Analysis (OMA) ...of the remaining half part of the bridge.•Bridge’s modal properties sensitivity to different scour levels.
This paper investigates the problem of flood-induced scour on masonry arch bridges through the analysis of a real case study, Rubbianello Bridge. This is a multi-span masonry arch bridge located in Central Italy, which suffered the collapse of two of the seven spans due to foundation scour during a severe flood in December 2013. The study has a twofold aim: to evaluate with a numerical model the level of scour which led to the bridge failure in 2013 and the corresponding collapse mechanism, and to assess the sensitivity of the bridge’s modal properties (vibration frequencies and mode shapes) to different levels of scour. An accurate nonlinear three-dimensional model of the bridge is developed, whose elastic properties are calibrated to match the results of dynamic identification tests performed via Operational Modal Analysis (OMA) on the remaining portion of the bridge. A numerical simulation of the effects of the scour hole progression is also performed on the full bridge, according to recently proposed techniques. The study results provide useful insights on both the cause of collapse of the bridge and the suitability of OMA for bridge scour monitoring.
Ring rolling is a process to manufacture seamless rings. The process is characterised by high non-linearity, asymmetry, unsteady state and non-uniformities in plastic strain and temperature ...distribution in the ring cross-section. Inhomogeneities in distribution of plastic strain and temperature have significant effects on deformation behavior, microstructure and mechanical properties. Fishtail defect, one of the form defects, is also a major concern. In this study, a reliable coupled 3D thermo-mechanical finite element model of the ring rolling process was developed using dynamic explicit code in ABAQUS/Explicit environment. Nine simulations with different combinations of feed rate and rotational speed were ascertained using Central Composite Design (CCD). CCD model is an integral part of Response Surface Methodology (RSM). Strain and temperature heterogeneities and fishtail defect were predicted using the simulated models. Coefficient of Variation (CoV) was introduced as a heterogeneity index for strain and temperature analysis. The fishtail coefficient was used to quantify fishtail defect. ANOVA was carried to find out the significant factors and interactions affecting the ring rolling process. Feed rate was found to be the only significant factor in the range of parameters studied. Multi-response optimization was performed to find out the feed rate at which the process is most optimized with an aim to minimize both strain and temperature heterogeneity and fishtail defect. Feed rate of 1.61 mm/s was found to be the most optimized process parameter.
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