Numerical Modelling Strategy Research Articles

Multiscale viscoplastic modeling of recycled glass fiber-reinforced thermoplastic composites: Experimental and numerical investigations

One of the main challenges facing fiber-reinforced polymer composites is the lack of options for end-of-life recycling. The environmental impact of waste materials disposed of at landfill sites, by incineration, or by erratic dispersion in the environment is accelerating the need to find innovative solutions to increase the value of recycled materials. This research aims to investigate the relationship between microstructural parameters and the mechanical properties of a recycled thermoplastic composite material. The latter is processed by thermocompression molding of a polyamide (PA66) matrix reinforced with chopped glass strands. An innovative approach is proposed to link the local microstructure of the composite to the mechanical behavior of the recycled material. It exploits an experimental characterization of the material microstructure using optical microscopy and X-ray micro-computed tomography (mCT). The experimental findings are implemented into a numerical modeling strategy to mimic the flexural behavior, based on a micromechanical approach coupling mean and full-field analysis. The region of interest is reconstructed from detailed 3D images using a modified random sequential adsorption (MRSA) algorithm, while other regions are modeled as homogenized macro-scale continua. Furthermore, the abilities of the proposed approach are proven by incorporating the viscoplastic behavior of the random heterogeneous material induced by the polymer matrix. The originality of the present research consists of the multi-scale FE analysis and the experimental validation for the viscoplastic behavior of the recycled composite material, taking into account influences from the microstructure.

An integrated inverse numerical–experimental approach to determine the dynamic Mode-I interlaminar fracture toughness of fibre composites

A combined numerical–experimental methodology is presented to determine the dynamic Mode-I fracture properties of Fibre-Reinforced Polymer (FRP) composites. The experimental aspect consists of a modified Wedge-Double cantilever Beam (WDCB) test using a Split Hopkinson Pressure Bar (SHPB) set-up followed by a numerical inverse modelling strategy using cohesive-zone approach. The proposed method is inherently robust due to the use of three independent comparison metrics namely, the strain–displacement response, the crack length history and the crack opening history to uniquely determine the delamination properties. More importantly, the complexity of dealing with the frictional effects between the wedge and the DCB specimen is effectively circumvented by utilising appropriate acquisition techniques. The proposed methodology is applied to extract the high-rate interlaminar fracture properties of a carbon fibre reinforced composite, IM7/8552 and it is further shown that a high level of confidence in the calibrated data can be established by adopting the proposed methodology.

Pore size distribution evolution in pellets based bentonite hydration: Comparison between experimental and numerical results

Several nuclear waste disposal concept designs take advantage of bentonite based materials to seal underground galleries and shafts. Safety assessment and long-term predictions of the material behaviour have been the main objective of a number of experimental campaigns and of constitutive models development. All these studies have underlined that the multi-porosity bentonite structure affects undeniably the strongly coupled hydro-mechanical processes taking place during water saturation. Due to this, in recent years, many classic experimental tests on unsaturated soils have been performed in conjunction with multi-scale observation techniques (for instance MIP, i.e. mercury intrusion porosimetry analises). Despite the well-known limitations of such observation methods, they provide interesting quantitative measurements in terms of pore diameters families, which differ by several orders of magnitude, and their distribution with respect to different assemblies' types (namely pellets mixtures and compacted bentonite blocks). On the other hand, very few studies have been focusing on the role of such pore size distributions with respect to the hydro-mechanical response, both from an experimental and a numerical point of view. The aim of this paper is to present the experimental campaign and the numerical modelling strategy adopted to analyse the role of different pore size distributions characterising MX-80 bentonite in different forms (i.e. 32 mm pellets mixture, 7 mm pellets mixture and compacted sample surrounded by gap) with same overall dry density during isochoric hydration tests. Taking advantage of multisensor-equipped cells and post-mortem analyses and of the finite element code LAGAMINE, the hydro-mechanical response of these bentonite assemblies is examined. Experimental and numerical outcomes result in good agreement and provide complementary information regarding the features of each assembly type.

Finite Element Model to Predict the Impact of Wrinkles on Wind Turbine Blades

Among the manufacturing defects of wind turbine blades, wrinkles are critical to the blade performance, affecting the structural integrity. Therefore, this paper introduces three-dimensional numerical models of laminates representative of a wind turbine blade with artificial wrinkles. The models are verified against static tension-compression experimental tests of laminates embedded with two types of wrinkles. The results show a good correlation between numerical prediction and experimentally obtained stiffness behaviour. The outcome of this analysis proves the validity of the numerical modelling strategy applied to evaluate the behaviour of laminates with wrinkles for a static loading situation.

Experimental research and numerical analysis on mechanical behavior of lightweight-design precast bent caps with large cantilevers

Two innovative lightweight-design schemes for large cantilevered precast bent caps (PBCs) commonly used in China are proposed in this study. In Scheme 1, a monolithic bent cap is divided into two symmetrical precast pieces that are parallel to the bent cap center line (hereafter referred to as PPBCs) and connected together by a cast-in-place wet joint. In Scheme 2, U-shaped and inverted U-shaped cross-section bent caps are designed to facilitate monolithic precast. Four scaled bent cap specimens are loaded monotonically to study the crack development, failure mode, deformation of the cantilevers, and ultimate load-carrying capacity. The test results show that all the specimens failed in the desired bending. However, the connectivity of the two precast pieces in the PPBCs was damaged after cracking occurred in the wet joint, leading to a slightly decreased ultimate load-carrying capacity, compared to the corresponding monolithic bent cap. The tensile stresses of the stirrups in the cavities of the U-shaped and inverted U-shaped cross-section bent caps were larger than those at other positions. Therefore, the arrangement of the stirrups should be strengthened in the cavities. The numerical modeling strategy validated by the test results was used to predict the mechanical behavior of full-scale lightweight-design bent caps from construction to final failure. The analysis results indicated that, all lightweight-design PBCs remained uncracked in both the construction and service stages. Finally, the PPBC and hollow cross-section PBCs failed under load combinations that were 1.9- and 1.7-time the Strength I load combination.

Design and numerical modelling strategy to form Tailored Fibre Placement preforms: Application to the tetrahedral part with orthotropic final configuration

Tailored Fibre Placement (TFP) allows manufacturing net shape preforms with continuously varying orientations and thickness. This additive technology, combined with forming, enables the design of fibre reinforced composite parts with optimized fibre orientations. A new modelling strategy to simulate the forming of thin dry TFP preform without backing material is proposed. The finite element model is based on an embedded element formulation, which assumes the stitching yarn to act as a bond between fibre tows of adjacent layers. Fibre tows are modelled with 2-node beam elements having independent generalized stress stiffnesses. The forming of a tetrahedral shape with orthotropic final configuration is addressed both experimentally and numerically to validate the proposed approach. The tetrahedral shape has a direct industrial application since it corresponds to corner brackets. This study also demonstrates the ability to improve the mechanical properties of engineered part using the hybrid TFP-forming process.

Numerical modelling strategies for reinforced 3D concrete printed elements

Extrusion-based 3D concrete printing (3DCP) prompts a new age of reinforced concrete structures by virtue of the exponential advancements in process, control, material, and fresh-state analysis technologies. Notwithstanding these advancements, latency exists in the numerical analysis of complex geometric forms produced by 3DCP technology. In this research, two finite element (FE) modelling strategies are proposed for the numerical analysis of 3DCP building elements. The objective of these models is to predict the hardened state structural capacity and failure mechanisms of singularly and dually reinforced concrete deep beams under various loading configurations. To validate the proposed FE modelling strategies, the reinforced 3DCP deep beams are experimentally evaluated. An analogy between masonry and 3DCP structures provides premise to the presented FE modelling strategies, and succinct descriptions of the respective modelling strategies, adaptions to the 3DCP design space, and material model prescriptions are provided. Strikingly, the recommended input parameters provide sound agreement with the experimentally evaluated configurations, with all simulations exhibiting a load carry capacity within 14% of the experimental observations. Not only is the load-displacement response deemed appropriate, but also the numerically produced cracking patterns, placing confidence in the proposed numerical simulation strategies. Furthermore, it is shown that the advent of a 2D plane stress simplification of the fibre-reinforced hollow beam geometry yields adequate agreement while significantly reducing the computational expense required to simulate the nonlinear response of anisotropic printed composites. • Design and fabrication rules to ensure structural integrity in 3DCP elements is presented. • The mechanical performance of reinforced 3DCP beams is experimentally investigated. • Two hardened state anisotropic numerical simulation frameworks for 3DCP are proposed. • A 2D plane stress simplification of cellular infill geometry is proposed and validated.

Numerical modeling of the post-fire performance of strap-braced cold-formed steel shear walls

Strap-braced, cold-formed steel framed walls are frequently used as the lateral force resisting system in cold-formed steel construction. While the behavior of these walls has been studied under lateral loading and (to a lesser extent) under fire conditions, there is a need to comprehend the influence of multi-hazard interactions, in particular the effect of fire pre-damage on the lateral load resistance of the walls. In this paper, a numerical model of a strap-braced cold-formed steel wall is developed to analyze the thermal and structural response when subjected sequentially to fire followed by shear deformation. The numerical model is validated against full-scale experiments. Coupon tensile tests are conducted to characterize the post-fire properties of the cold-formed steel that are used as inputs to the model. The results show that the numerical model can capture the post-fire response of the cold-formed steel walls including the wall strength, stiffness and ductile failure by yielding of the strap. The lateral behavior of the walls depends primarily on the maximum temperature reached in the cold-formed steel members and the resulting residual properties. Thermal analysis by the finite element method can be used to predict the maximum temperatures across a wall section under a variety of design-relevant fire scenarios, but the results are strongly affected by the quality of the data on thermal properties and by the loss of integrity of the gypsum sheathing. This study validates the numerical modeling strategy and suggests that the post-fire lateral capacity of the walls can be predicted from ambient temperature methods with use of the cold-formed steel residual mechanical properties.

Macro-modeling approach incorporating fiber plastic hinge for reinforced concrete frames with masonry infill

An indefinite guide from technical codes around the world leads to confusion and repudiation of masonry infill during the structural design and analysis of infilled frames. In recent years, the rising interest in nonlinear seismic analysis has called for a robust yet simple numerical modeling strategy to model the seismic behavior of reinforced concrete frames with masonry infill. This study aims to propose a reliable macro-modeling approach that incorporates fiber plastic hinge to simulate the in-plane hysteresis response of reinforced concrete frames with masonry infill. An existing constitutive law and a simplified pivot hysteretic law were fine-tuned to describe the nonlinear behavior and cyclic response of the equivalent diagonal strut representing solid clay brick masonry. A comparison with experimental observations showed that the proposed numerical modeling strategy can satisfactorily predict the in-plane global response of infilled frames.

Seismic performance of bridges with novel SMA cable‐restrained high damping rubber bearings against near‐fault ground motions

AbstractThis study presents a novel type of shape memory alloy (SMA) cable‐restrained high damping rubber (SMA‐HDR) bearing, which is particularly suited to near‐fault (NF) regions where the pulsing effect potentially exists in the ground motions. The working mechanism of the bearing is first described, followed by an experimental investigation on a full‐scale SMA‐HDR bearing specimen. The test results confirm the efficient restraining effect offered by the SMA cables, which contribute to 65% and 24.4% of the lateral load resistance and total energy dissipation, respectively, prior to the initial fracture of the SMA cables. The failure of the cables is initiated near the end grip where moderate stress concentration exists at this region. Following the experimental study, the numerical modeling strategy for the bearing is discussed, and a case study is then presented, demonstrating the application of the SMA‐HDR bearings in the Datianba #2 highway bridge, a real project that first adopts the proposed bearings in the world. A simplified design process is introduced for the bridge with novel SMA‐HDR bearings to mitigate the potential damage during strong earthquakes especially the NF ones. The system‐level analysis on the prototype bridge shows that the novel SMA‐HDR bearings equipped with ten 7×7×1.2 SMA cables in each bearing could reduce the average maximum bearing displacement (MBD) by nearly 30% compared with the conventional bridge with HDR bearings. The application of the novel SMA‐HDR bearing can significantly alleviate the pounding effect, especially under the NF earthquakes. The presence of the SMA cables tends to increase the maximum force response of the piers, but this effect is minor and under control.

Numerical modeling of localized fire exposures on structures using FDS-FEM and simple models

This paper investigates different numerical modeling strategies for evaluating temperatures in structures subjected to localized fires. Three simple fire models and two methods to interface computational fluid dynamics models with finite element thermal analyses are reviewed. Based on the field of application of each model, a decision flowchart is proposed to select the fire model and strategy suited to the problem. Validation is conducted against three experiments on steel members subjected to localized fires. Results show that the coupling between computational fluid dynamics and finite element analysis through the adiabatic surface temperature is a versatile method able to capture the member temperature in the different experiments in this study. The use of an automatic transfer interface using a transfer file with gas temperatures and radiant intensities is an efficient alternative when the member is outside the fire area and far enough that it does not significantly influence the fire development. The member should not be present in the FDS model when using the interface method. The simple models tend to yield more conservative predictions compared with the experimental results.

Seismic and Energy Integrated Retrofitting of Existing Buildings with an Innovative ICF-Based System: Design Principles and Case Studies

This work proposes an innovative integrated retrofitting system aiming to improve both the seismic and energy performance of existing reinforced concrete and masonry buildings. The system is based on engineered insulating concrete form panels, installed on the outside of existing buildings as a shell exoskeleton. A key major advantage of the proposed system is that it addresses the contemporary improvement of seismic and energy performances of existing buildings in a single installation stage, operating exclusively from outside of the building. The insulating formworks are ad hoc prefabricated in a factory on the base of the specific geometry of the existing buildings so as to greatly maximize the ratio between overall retrofitting benefits and costs and at the same time to simplify the installation procedures. The objectives of the presented research are, on one hand, to highlight the major structural issues that the system aims to address, and on the other hand to illustrate the main characteristics and combined benefits of the proposed retrofitting system. From a structural point of view, the proposed system is conceived to behave as a non-dissipative structure with regard to seismic actions, and the lateral strength and stiffness of the structural elements are designed accordingly. An analytical design approach is proposed and validated using the available data from an experimental test performed on a full-scale simple building. Moreover, numerical modeling strategies for the proposed system are illustrated for two complex case study buildings. The results of the analyses show a considerable increase in lateral stiffness of the retrofitted buildings that, considering the non-dissipative behavior of the elements, leads to a relevant reduction of seismic deformation demand on existing structural elements.

Multiscale numerical investigation on failure behaviour of three-dimensional orthogonal woven carbon/carbon composites subjected to pin-loading

On the basis of the experimental results in previous work, a multiscale numerical modeling strategy on the failure behaviour of three-dimensional orthogonal woven carbon/carbon composites under pin-loading was presented. In consideration of the complexity of internal woven architecture, the finite element analysis at micro-/meso-/macro-scale levels was performed to exhibit the effective material properties and mechanical behaviour. The geometric models were reconstructed via X-ray tomography technology to obtain feasible configurations based on actual microstructure, meanwhile the models considered the fibers random arrangement in the yarn and voids stochastic distribution in the matrix. The anisotropic composites damage evolution was characterized by Murakami-Ohno damage theory. Additionally, for a further exploration on the practical bearing failure mode, the macro-scale open-hole plate model was established using mesh superposition method to expose the damage mechanism of each component in composites at hole edge, and the numerical predictions agreed reasonably well with the experimental results.

Caloric devices: A review on numerical modeling and optimization strategies

Caloric devices: A review on numerical modeling and optimization strategies

Effects of Corrosion on Compressive Arch Action and Catenary Action of RC Frames to Resist Progressive Collapse Based on Numerical Analysis.

Many negative factors can influence the progressive collapse resistance of reinforced concrete (RC) frame structures. One of the most important factors is the corrosion of rebar within the structure. With increasing severity of corrosion, the duration, robustness, and mechanical performance can be greatly impaired. One specific side effect of rebar corrosion is the significant loss of protection against progressive collapse. In order to quantify the effects of rebar corrosion on load-resisting mechanisms (compressive arch action (CAA) and tensile catenary action (TCA)) of RC frames, a series of numerical investigations were carried out in this paper. The previous experimental results reported in the literature provide a benchmark for progressive collapse behavior as a sound condition and validate the proposed numerical model. Furthermore, based on the verified numerical model, the CAA and TCA with increasing corrosion and an elapsed time from 0 to 70 years are investigated. Comparing with the conventional empirical model, the proposed numerical model has shown the ability and feasibility in predicting the collapse resistance capacity in structures with corroded rebar. Therefore, this numerical modeling strategy provides comprehensive insights into the change of load-resisting mechanisms in these structures, which can be beneficial for optimizing the design.

Numerical Analysis of Mechanical Damage in Ribbed Masonry Vaults under Differential Settlements

ABSTRACT The present study takes advantage of a parametric model, which allows one to create automatically complex structural models of ribbed masonry vaults. Two numerical modelling strategies are discussed: a 3D continuum and a 3D contact-based model. The effects of settlements are studied by imposing vertical displacement at the vault supports up to collapse. Predictions of each modelling strategy are compared with actual damage observation. A representative square vault of Milan Cathedral is studied here, aiming to understand the causes of the damage documented through the years. The structure is noted to have suffered structural damage in the vaulting system due to a long history of soil settlements. The geometry is based on a photogrammetric scanning, and the three-dimensional solid models are created through parametric reconstruction procedures, including details such as springing, arch, ribs, web, and rubble-fill. Both modelling strategies allow to highlight the vulnerability of masonry vaults due to settlements. Significant differences in prediction capabilities are noted when large displacements and separation of elements are involved. The simulations show the possibility of predicting and interpreting different complex damage phenomena as arch block damage or sliding, and web–arch detachment, which is frequently observed in historical structures.

A TWO-PHASE MODELING METHOD BASED ON COHESIVE ELEMENTS FOR MASONRY ARCHES

To simulate the non-homogeneity of masonry materials, a two-phase numerical modeling strategy based on Cohesive elements is proposed. In the proposed method, masonry is considered as a two-phase material, which consists of stone blocks and mortar joints. Solid elements are used to simulate the blocks. A nonlinear constitutive model is introduced to describe their failure behavior. Cohesive elements are inserted between adjacent blocks to consider the shear and tensile failure of the mortar. The effectiveness and applicability of the method are verified by comparison of experimental tests and numerical simulation. The influence of sensitive parameters, such as the shear friction coefficient μ and loading position, on the strength of the arch bridge is analyzed by numerical simulation. The results show that the two-phase numerical model of stone masonry based on Cohesive elements avoided the difficulty in continuous numerical methods in simulating the non-homogeneity of masonry materials, and provided important information for the ultimate strength evaluation of stone arch bridges, such as the load displacement curves and failure modes. In addition, the failure mechanism of the main arch was determined by the bending and shear characteristics of the arches, especially the shear fiction coefficient of the mortar joints.

Numerical modelling strategy for predicting the response of reinforced concrete walls using Timoshenko theory

In recent decades, different macro-models have been proposed for simulating the behaviour of concrete shear walls because of their significant role in the seismic performance of urban buildings. The ability of Timoshenko's beam theory to evaluate the behaviour of slender and moderate-aspect-ratio concrete shear walls was evaluated in this work. For this purpose, a non-linear displacement-based Timoshenko fibre element was first added to OpenSees software. A new constitutive model based on modified compression field theory was used for the stress–strain relationship of the materials. To validate the element and the materials used, the results of the numerical model were compared with a set of laboratory tests of concrete shear walls subjected to cyclic and seismic loads (shaking table tests). Evaluation of the numerical model and the experimental results revealed that the analysis procedure used to model the reinforced concrete walls predicted their overall and local responses with acceptable accuracy. It can thus be used as a reliable tool for the analysis of slender and moderate-aspect-ratio concrete shear walls.

Numerical modelling strategies using implicit and explicit methods to simulate quasi-static and dynamic three-points bend fracture tests of a ductile steel

Three-point bend fracture tests have been conducted at different loading rates with a quadratic martensitic steel. The failure energy has been found to increase with loading rate. To get insights in this increase a numerical investigation has been undertaken with different strategies using ABAQUS and IMPETUS softwares in order to address quasi-static and dynamic loading conditions. Simulations were conducted with the ABAQUS software in order to carry out a comparative analysis of both implicit and explicit approaches. In addition to standard Finite Element Method (FEM) applied to quasi-static and dynamic conditions, the eXtended-Finite Element Method (X-FEM) was applied to quasistatic conditions. In both approaches, implicit and explicit, crack initiation and propagation were governed by a critical plastic strain threshold combined with a displacement-based damage evolution criterion. Simulations conducted with the IMPETUS software use an explicit approach and second order elements for both quasi-static and dynamic loading conditions. A node-splitting method using an energy-based damage criterion was employed to simulate the crack initiation and propagation. Experimental data and numerical results have been compared, allowing to determine the ability of these two softwares to simulate accurately three-point bend fracture tests.

Sandwich Panels with Polymeric Foam Cores Exposed to Blast Loading: An Experimental and Numerical Investigation

Sandwich panels have proven to be excellent energy absorbents. Such panels may be used as a protective structure in, for example, façades subjected to explosions. In this study, the dynamic response of sandwich structures subjected to blast loading has been investigated both experimentally and numerically, utilizing a shock tube facility. Sandwich panels made of aluminium skins and a core of extruded polystyrene (XPS) with different densities were subjected to various blast load intensities. Low-velocity impact tests on XPS samples were also conducted for validation and calibration of a viscoplastic extension of the Deshpande-Fleck crushable foam model. The experimental results revealed a significant increase in blast load mitigation for sandwich panels compared to skins without a foam core, and that the back-skin deformation and the core compression correlated with the foam density. Numerical models of the shock tube tests were created using LS-DYNA, incorporating the new viscoplastic formulation of the foam material. The numerical models were able to capture the trends observed in the experimental tests, and good quantitative agreement between the experimental and predicted responses was in general obtained. One aim of this study is to provide high-precision experimental data, combined with a validated numerical modelling strategy, that can be used in simulation-based optimisation of sandwich panels exposed to blast loading.