Explicit Finite Element Model Research Articles

Behavior of steel fiber-reinforced coal gangue concrete beams under impact load

In order to promote the use of new sustainable steel fibers (SF) reinforced coal gangue aggregates (CGA) concrete, impact tests were performed in this paper. The impact resistance of steel fiber-reinforced coal gangue concrete was investigated using a self-developed drop-weight facility. The test variables were the CGA replacement rate (0 %, 50 %, and 100 %), the SF volume content (0 %, 0.75 %, and 1.5 %), and the drop height of the drop-weight (0.5 m and 1.0 m). Using 15 kg of hard steel as a drop-weight, the drop-weight impact test was performed on steel fiber-reinforced coal gangue concrete beams with a span of 300 mm; the damage pattern, impact reaction force-time, displacement-time relationships, and energy absorbed by steel fiber-reinforced coal gangue concrete beams were studied. The test shows that, compared with natural aggregate, CGA reduces concrete's static mechanical properties and impact resistance, and adding SF improves the static mechanical properties and impact resistance of coal gangue concrete. As the CGA replacement rate increased from 0 % to 50 % and 100 %, the reaction force of impact of the specimens decreased by 2.54 %− 6.06 % and 3.69 %− 12.33 %. The SF volume content was increased from 0 % to 0.75 % and 1.5 %, and the reaction force of impact of the specimens was increased by 23.05 %− 32.34 % and 72.27 %− 81.84 %, respectively. The impact resistance of steel fiber-reinforced concrete beams under impact loading was investigated numerically using a nonlinear explicit finite element model in LS-DYNA. The Finite Element results were validated with experimental results. Based on the validated finite element model, a parametric study was carried out to investigate the effects of coal gangue replacement rate, steel fiber volume content, and drop height of the drop weight on the behavior of the beams. This study might provide a basis for the future engineering project applications of steel fiber-reinforced coal gangue concrete under impact conditions.

Ultrasonic wave propagation analyses in centrifugally cast stainless steel using solidification grain structure models

Several components of nuclear power plants are made from cast austenitic stainless steel (CASS) because of its high corrosion resistance and strength. CASS that is centrifugally fabricated in a rotating mold is used in primary coolant piping. In-service inspection based on ultrasonic testing (UT) has to be conducted for primary coolant piping in accordance with fitness-for-service codes. However, a high-accuracy evaluation of flaws in CASS components through UT is difficult because the ultrasonic waves are scattered and attenuated by the coarse grains, and the ultrasonic beam is distorted by the anisotropy resulting from the grain orientations. Some works have attempted to improve UT capability for CASS components. For more improvement, it is essential to understand how ultrasonic waves propagate in the solidification structure of CASS. Numerical simulations are a useful and reasonable way for this purpose. The simulation model should account for a three-dimensional grain structure. In this study, we prepared three different models of solidification structures for centrifugally CASS, and we fed these structures into an explicit finite element model to simulate the propagation of ultrasonic waves. Afterward, we compared the simulated wave propagations with those measured by a laser Doppler vibrometer to determine an appropriate model that showed good agreement between the simulated and experimental results.

Unreinforced masonry walls under two-way out-of-plane bending: Comparison of FE model predictions with analytical models

Four existing design guidelines based on the virtual work method have been compared to predict the out-of-plane (OOP) bending capacities of unreinforced masonry (URM) walls to one-way and two-way actions. The two-way OOP bending design equation as per the Australian masonry standard (AS 3700) and the three subsequent models developed by other researchers are based on specific wall geometries, support conditions, dimensions and strengths of masonry units and mortar. Due to limited experimental data available on URM walls under two-way bending, it is difficult to carry out a detailed investigation of the performance of these two-way design models against all the design parameters. This paper applies the finite element (FE) modelling technique to generate data and extensively investigate the influence of support conditions, pre-compression and aspect ratio on the two-way OOP bending capacity of URM walls. An explicit FE model previously developed by the authors where masonry is macroscopically modelled as an anisotropic composite material, is used for this purpose. Performances of three key parameters (i.e., moment capacity under horizontal bending and diagonal bending and torsional shear strength of masonry) that differentiate the four design models are investigated against varying levels of vertical pre-compression and flexural tensile strength of masonry. The OOP bending capacity predicted by the FE model is compared with the predictions of the design models. Results show that three out of four design models generally overpredict the two-way OOP bending capacities of square and taller walls. Further refinement to the AS 3700 design equation has been proposed in a modified model. The outcomes of this research will help to improve the design of masonry walls under OOP bending.

Validated, high-resolution, non-linear, explicit finite element models for simulating screw - bone interaction

Background and ObjectivePrimary stability evaluation of screw implants through pull-out or push-in experiments is commonly used to investigate the mechanism of screw loosening. Numerical models simulating these testing methods could provide an enhanced understanding of the underlying attachment mechanisms as well as save time and cost in the development of new screws. However, previous numerical models have been limited by compromises between modelling the trabecular structure at high resolution versus incorporating sophisticated mechanical properties and boundary conditions, leading to overestimated mechanical performance. The aim of this study was to overcome these limitations. MethodsWe developed explicit models incorporating the microstructure of trabecular bone, with frictional contact, and a non-linear material model incorporating damage. One model digitally inserted the screw into the trabecular bone structure using Boolean operations, while another model simulated the screw's rotational insertion. ResultsThe results showed a strong correlation between numerical and experimental results (R2: 0.54–0.93) for force-displacement response in terms of stiffness and strength. We found that the damage induced by the screw insertion process is an important factor to be considered, as the absence of modelling it led to an overestimated stiffness in previous studies. ConclusionsThe study highlights the importance of including frictional contact and also identified screw insertion damage as an important part of the simulating screw-bone interaction. Our findings demonstrate the potential of explicit finite element models for accurately replicating experimental push-in results and optimizing orthopaedic screws. The code is available at https://github.com/zhou436/Bone-Screw-Constructs-eFEM.

Numerical investigation on orthogonal cutting and damage response of CFRP/Ti6Al4V stacks

CFRP/Ti6Al4V stacks are widely employed in aerospace, automotive and marine applications owing to their superior properties. However, machining these stacked structures pose challenges due to the intrinsic difference in the mechanical properties of CFRP and Ti6Al4V. Such difference can induce distinct failure mechanisms and chip formation processes compared to those observed in individual materials. This paper presents an explicit finite element (FE) modeling to predict the cutting forces and analyze the induced damage during the orthogonal cutting process. The proposed FE model is validated using available experimental data for separate CFRP and Ti6Al4V conditions before being applied to simulate the cutting behavior of CFRP/Ti6Al4V stacks. The effects of fiber angles, cutting sequences and cutting parameters on the cutting performance and damage mechanism of CFRP/Ti6Al4V stacks are investigated in detail. This work provides insights into the cutting behavior of CFRP/Ti6Al4V stacks and facilitates the optimization of machining process for such composite system.

Effects of average number of platelets through the thickness and platelet width on the mechanical properties of discontinuous fiber composites

In this study, we experimentally and numerically investigate the evolution of the tensile material properties of Discontinuous Fiber Composites (DFCs) with an increasing average number of platelets through the thickness for two different platelet widths.The results show that both the number of platelets and the platelet width have significant effects on the tensile modulus and strength. We find that not only the average mechanical properties but also their coefficients of variation change according to the different DFC mesostructures.To understand the relationship between material morphology at the mesoscale and corresponding material properties, we developed a random platelet mesostructure generation algorithm combined with explicit finite element models. Leveraging the computational tools, we find that moduli and strength increase with increasing average number of platelets through the thickness. The increasing trend continues until reaching an asymptotic limit at about 45 layers through the thickness for the narrow and 27 layers for the square platelets.In the study, we address the importance of having accurate simulations of the mesostructure to match not only the average modulus and strength but also their associated coefficients of variation. We show that it is possible to accurately predict the tensile material properties of DFCs, including their B-basis design values. This is a quintessential condition for the adoption of DFCs in structural applications.

Analysis of the texture evolution during multipass tube spinning of a TA15 alloy using the crystal plasticity finite element model

In this study, we present an explicit crystal plasticity finite element model (CPFEM) to investigate the texture evolution during multipass tube spinning of a TA15 alloy. The texture formation mechanism is further revealed by analyzing grain rotation and slip behaviors. The results indicate that, for the grains whose c-axes are far from the normal direction (ND), the basal <a> slip is dominant under the significant compression deformation state of spinning. Therefore, the c-axis gradually turns toward the ND. However, for the grains whose c-axes are close to the ND, the contribution ratios of other slip systems increase, especially that of prism <a>. Under these conditions, the c-axis deviates slightly from the ND, and grains mainly rotate around the c-axis. Therefore, most of the {0001} poles cluster around the ND and {10-10} poles are distributed in the rolling-hoop plane, exhibiting an obvious basal texture component. These results imply that the CPFEM can effectively predict the formation of basal texture component during spinning. With an increase in the number of spinning pass, the texture distribution becomes slightly inhomogeneous along the ND owing to the uneven distribution of macroscopic strain. In addition, the grain rotation first increases and then decreases with deformation. The smaller grain rotation at the first pass is because a large number of basal <a> preferentially operates in the grain with favorable orientation, resulting in localized inhomogeneous deformation. The decrease at larger deformation is due to the lower Schmidt factor of basal <a>, which limits the grain rotation.

Predicting the weld zones size in FSSW of 304L stainless steel plates by mathematical model based on RSM

The 300 series austenitic stainless steels are widely used in industries due to their special properties. High heat in fusion welding reduces the properties of these steels and causes many problems. Therefore, stir friction spot welding, which is a type of solid state welding, is useful and widely used in high-tech industries. In this paper, a 3D dynamic explicit finite element model is developed to simulate the friction stir spot welding of 304L stainless steel plates. Using this model, the temperature distribution and the size of weld zones (thickness of weld zones) are obtained. Then, by experimental study, the results of the temperature and the size of weld zones were obtained to be a criterion for comparing and validating the numerical results. Microstructure and hardness of these zones are determined experimentally. Finally, a mathematical model based on the response surface methodology is proposed to predict the size of weld zones. Good agreement between the numerical results that are produced by the finite element simulation, the proposed model and the experimental data is observed. The results show the maximum temperature level appears in the stir zone and it reduces by moving from the weld center. Also, by increasing the rotational speed, plunging depth and dwell time of the tool, the size of both the stir zone and the heat affected zone increase to a peak value and then the size of the latter zone decreases.

Airfield pavement resiliency assessment against extreme dynamic events by explicit axisymmetric finite element models

Infrastructure resiliency has become an essential element in ensuring community recovery after unexpected events. In airfield pavement, resilience can be achieved through an improved design approach by understanding the fundamental elements of damage mitigation and thus allowing rapid recovery. The objective of this study was to numerically evaluate easy-to-implement alternatives for mitigating damage in rigid airfield layered pavement systems when subjected to dynamic events such as blasts or high-velocity impacts. This was accomplished by developing an efficient axisymmetric explicit finite element model, which served as an analytical tool for the study. The model was developed in LS-DYNA and the methodology consisted of a comprehensive parametric analysis. The results showed that the concrete pavement layer parameters—mass density and compressive strength—have the most significant effect on the damage to the pavement when subjected to extreme dynamic events. The material parameters for the pavement layers were optimized to minimize the damage, caused by dynamic loads, achieving more than 70% damage mitigation. Furthermore, adding a granular base layer to the rigid airfield pavement design reduces the concrete pavement layer damage by almost 40%. An asphalt concrete overlay reduces the concrete pavement layer damage by about 55%. Moreover, adding an asphalt concrete overlay to the optimized rigid airfield pavement design reduces the damage by 10%. In contrast, adding a granular base layer to the optimized rigid airfield pavement design is ineffective.

Performance of LG window systems with different materials under extreme static loading

Laminated glass (LG) is created by bonding two or more glass layers together with one or more polymer interlayer(s). LG may significantly lower the risk of injury from broken glass because the polymeric interlayer retains the glass pieces, especially when subjected to explosive threats. Many interlayer materials have recently been used in LG panels, but the effects on the performance of glass thickness and type, interlayer thickness and type, and hybrid interlayers are not well known. In this work, we report on new implicit and explicit nonlinear finite element models for simulating pressurized water-chamber-like quasi-static tests. The numerical models were validated using 18 by 18 in. LG tests. This study shows that the resistance function of LG can be well predicted numerically and can be used as a tool to study the effects of various glass and interlayer types and configurations. Explicit solutions had a slightly greater resolution in predicting the fracture behavior and post-peak response and captured the distinct failure points of the inner and outer glass panes. Implicit calculations maintained high levels of accuracy and were orders of magnitude faster than the explicit simulations. Using the implicit method, a parametric study was conducted on 38 by 66 in. LG to determine the effects of glass and interlayer thickness, size, and layup configuration. The LG resistance function was improved within the pre-cracked stage by increasing interlayer thickness. Ionoplast SentryGlas® interlayers were shown to be the strongest of the three types considered. Additionally, unique hybrid interlayers were simulated and indicated that strength and bonding can be maximized using various hybrid configurations.

Numerical and experimental investigations of low-velocity impact on composite overwrapped pressure vessel with different stacking sequences

Composite overwrapped pressure vessels are designed to contain fluids that operate under high pressures. In addition to internal pressure, the design needs to account for out-of-plane loading in the form of low-velocity impact. In this study, a numerical analysis of four models of composite overwrapped pressure vessels with different stacking sequences is performed. A three-dimensional explicit finite element model using multi-layer stacked shell elements was used in the impact zone region to obtain reasonable computation time. Utilizing the bilinear traction-separation law, cohesive zone elements were used to simulate the delamination failure and as bonding between eight layers of CFRP covering the aluminum liner. The simulation results were then validated using drop-weight impact tests, which revealed that the response of contact force to impact time was comparable for both types of analysis. Prediction of failure was carried out by assessing the quantity of energy absorbed by the CFRP layers and was confirmed by shell element data that failed during simulations. In addition, the Hashin damage model confirmed that the matrix tensile failure mode was the predominant failure mode for all discussed impact scenarios. Model-A with Al + [90]8 stacking sequence was found to have the highest impact resistance based on the prediction of the composite’s failure area and the energy absorbed by the CFRP layers. Furthermore, it was found that COPVs with combinations of helical and hoop sequences tend to have larger areas of delamination due to high interlaminar shear stress between the CFRP layers.

Experimental and numerical investigation of cold-formed steel telescopic studs under compression

This paper presents a thorough experimental and numerical investigation into the structural behaviour of a novel cold-formed steel (CFS) telescopic stud system under axial compression. A total of 40 specimens were tested, considering variations in screw configurations, steel grades, and section thicknesses. The test results revealed that tilting and bearing led to failure in all screw connections. In comparison to the single-screw connection with a gap at the middle of the web, the telescopic studs with 2 screws in the web, 2 screws in the flanges, and 4 screws in both the web and flanges showed approximately 35–37% higher strengths. A nonlinear explicit dynamic finite element model was then developed and validated against the test results in terms of its connection strengths and failure modes. The experimental results were compared with the design strengths determined by the current design standards (AISI S100 (2016), AS/NZS 4600 (2018), Eurocode 3 (2006), BS5950–5 (1998) and GB50018 (2002).). The comparison results revealed that the AISI S100 (2016) and AS/NZS 4600 (2018) are conservative, underestimating the connection strengths of telescopic studs with different screw layouts by 1–13%.

Using the fatigue crack initiation parameter for prediction of the crack location on a curved track by 3D-FE analysis

Dynamic modeling of wheel-rail interaction is significant in accurate fatigue analysis of railways. Both location and magnitude of the contact stresses in the contact area must be evaluated accurately and efficiently via computational tools. In curved railway tracks, the distribution of the force exerted on the wheel is complex as it is multiaxial rather than uniaxial; thus, a more comprehensive computational model is required. In this work, a numerical procedure is developed to investigate the fatigue crack initiation on the curved tracks. The Universal Mechanism software is used to specify the spectrum of axial wheel force as input to a three-dimensional explicit finite element model to obtain the resulting stresses at the wheel-rail contact region. A critical element with the maximum von Mises stress value is treated as the element where the fatigue crack is most probably to be initiated. In this element, the critical plane method is used to determine the orientation of the crack initiation. The effect of the radius and slip ratio on the exact site of fatigue crack initiation is established in this approach, and the contact point influence on the fatigue crack initiation parameter is investigated. The proposed model successfully predicts a practical wheel-rail dynamic response to cyclic loading, applying the geometry of the curved track.

An efficient detailed layer model for prediction of separator damage in a Li-Ion pouch cell exposed to transverse compression

Li-ion pouch cells can be understood as thin-layer laminates. Pressure loads normal to flat electrodes can cause failure or thermal runaway. However, detailed models for investigating transverse pressure loads in which each layer is resolved are computationally intensive. This paper outlines two approaches for time-efficient yet accurate detailed explicit finite element models of a cell. Both approaches are characterised by the fact that they are divided into in-plane and out-of-plane behaviour. The modelling of interlaminar contacts is completely omitted, to prevent parasitic contact compliance and efforts for contact handling. A discrete element formulation is used for a computationally efficient simulation of transverse loads. This prevents a reduction of the critical time step, which can result from transversal deformations. The difference between the two modelling approaches lies in the modelling of the out-of-plane behaviour. In the first approach, the behaviour in the out-of-plane direction is generated by characterising each component separately. The second approach assumes homogenous behaviour in the thickness direction. Both approaches rely on characterization data derived from component and cell tests. The cell models are validated against cell tests. Numerical results obtained with the two modelling approaches differ only slightly from the validation data.

Detection and Measurement of Pitting Corrosion using Short Range Guided Wave Scanning

Short range guided wave scanning is an inspection method enabling an indirect, quantitative measurement of remaining pipe wall thickness. It has seen widespread industrial use as an inspection solution for corrosion under pipe support (e.g. [1]). Pitting corrosion represents a significant challenge in industrial pipelines and its presence complicates short range guided wave scanning analysis as the wavelength used for inspection is larger than the diameter of small pitting-type defects. This work investigates the reflected signal from pitting corrosion, both in isolation and in the presence of larger corrosion patches, to improve the understanding of the complex signals received. This work provides the foundation and guidance for analysis techniques used in guided wave scanning. To achieve this a series of representative pitting defects with varying diameter and depth have been investigated using explicit finite element modelling. It is shown that using currently established analysis techniques, the pit depth can be quantified for pitting with a diameter larger than approximately 13 mm. Smaller diameter pitting may only be qualitatively detected at this time due to mode conversion occurring at the defect, which obscure features that are used to provide quantitative analysis of the defect depth. Quantitative sizing of defects where pitting is present will require further investigation.

Comparison of grain structure models for wave propagation analysis in centrifugally cast stainless steel

Centrifugally cast stainless steel (CASS) is widely used in primary coolant piping of pressurized water reactor plants because of its high corrosion resistance and high strength. An in-service inspection based on ultrasonic testing (UT) has to be conducted for weld joints of primary coolant piping on the basis of JSME Rules on Fitness-forService for Nuclear Power Plants. However, it is difficult to detect and size flaws in CASS components with high accuracy because of the following reasons: Ultrasonic waves are scattered and attenuated due to coarse grains, and anisotropic and heterogeneous properties in CASS lead to ultrasonic beam skewing. Numerical simulations are useful and reasonable ways for better understanding the ultrasonic wave propagation behavior in CASS. To effectively achieve this, the simulation model should include a three-dimensional (3D) grain structure. In this study, we modeled three kinds of the solidification grain structures of centrifugally CASS. One is obtained by using a cellular automaton method, another consists of many hexagonal columns with the same dimensions, and the other is transversely isotropic material. Then these structures were fed into an explicit finite element model for simulating wave propagation and the simulated results were compared with those measured by a laser Doppler vibrometer. Through the comparison, we investigated the applicability of these three kinds of solidification grain structure models to simulation for wave propagation.

Dynamic computational wear model of PEEK-on-XLPE bearing couple in total hip replacements.

Understanding wear mechanisms is a key factor to prevent primary failures causing revision surgery in total hip replacement (THR) applications. This study introduces a wear prediction model of (Polyetheretherketone) PEEK-on-XLPE (cross-linked polyethylene) bearing couple utilized to investigate the wear mechanism under 3D-gait cycle loading over 5 million cycles (Mc). A 32-mm PEEK femoral head and 4-mm thick XLPE bearing liner with a 3-mm PEEK shell are modeled in a 3D explicit finite element modeling (FEM) program. The volumetric and linear wear rates of XLPE liner per every million cycles were predicted as 1.965 mm3/Mc, and 0.0032 mm/Mc respectively. These results are consistent with the literature. PEEK-on-XLPE bearing couple exhibits a promising wear performance used in THR application. The wear pattern evolution of the model is similar to that of conventional polyethylene liners. Therefore, PEEK could be proposed as an alternative material to the CoCr head, especially used in XLPE-bearing couples. The wear prediction model could be utilized to improve the design parameters with the aim of prolonging the life span of hip implants.

Energy absorption characteristics of a super hexagonal honeycomb under out-of-plane crushing

Designing innovative honeycomb materials with improved energy absorption capacity is a long-term pursuit to provide adequate impact protection for crucial structural components. The edge-based design has been regarded as an effective strategy to enhance the mechanical properties and energy absorption of honeycomb materials. This paper proposes a novel super hexagonal honeycomb (SHH) structure to pursue better energy absorption capacities. Its geometry is derived from the outline of a hexagonal honeycomb. The crushing performance of the SHH is investigated based on the out-of-plane compression experiments, and an explicit finite element model is established to explore the crashworthiness characteristics of the structure. Furthermore, a theoretical model based on the simplified super folding element (SSFE) method is established to predict the mean crushing force during the crushing process. The comparison with the experimental and numerical results verifies its accuracy. Besides, the crushing mechanisms and collapse modes of the constitutive Y and V elements in the SHH are discussed. The parametric analysis of the crashworthiness of the SHH is conducted in terms of the cell-wall length ratio, sub-corner angle and hierarchy. The results reveal that the crashworthiness of SHH is much superior to traditional hexagonal honeycomb and presents 106%, 62%, 104% and 162% improvement in the mean crushing force, crushing force efficiency, specific energy absorption and volumetric energy absorption, respectively. This work can inspire future research on lightweight edge-based honeycombs with excellent energy absorption capacity.

Optimization of a temporary road traffic steel barrier using explicit finite element method and laboratory testing

Over a million people die in road crashes and tens of millions result injured or disabled each year, globally. Hence, there is a constant concern for improving the safety of the roads to protect road users, and those at the most risk, the road workers. Construction, maintenance, and utility work are constantly needed to ensure safety and functionality of roads and highways. Temporary road traffic barriers are used to separate passing traffic from the workspace and protect the workspace from an errant vehicle intrusion. Steel barriers are light, and their major advantage is rapid installation. These barriers are not anchored to the ground, and their behavior relies on the base-pavement friction, mass inertia, and stiffness of the system. The paper describes a methodology that was successfully applied for the development of a temporary road traffic steel barrier in compliance with the European specification EN 1317. The study included a simplified theoretical analysis of 178 barriers, static laboratory tests of three types of barrier connectors, development of explicit finite element models (EFEMs) of four selected barrier designs, and a full-scale crash test of the final barrier design. It is shown that static laboratory tests of complex connector systems can help to improve the design process and reduce the cost. The analysis and use of EFEMs was enough so that just a single full-scale crash test was sufficient for certification of the barrier design for use in Europe. The final barrier is compliant with the EN 1317–2 requirements for T1/W1 (TB21) containment level, which was confirmed by a full-scale crash test.

Bird strike simulation on a bonded Ti/CFRP leading edge of an engine fan blade

Bird strike represents a critical loading scenario for aeronautical structures, especially for engine fan blades. It is, therefore, of great importance both to protect the leading edge of the fan blade from impact damage and to be able to detect impact damage directly. In the present study, an explicit finite element (FE) model was developed using the LS-DYNA software to simulate bird strike on the leading edge of a CFRP fan blade protected by an adhesively bonded Ti layer. The model accounts for damage on the CFRP blade through a progressive damage modeling scheme and for debonding through a cohesive zone modeling scheme but not for damage on the Ti layer. For the modeling of the bird, the smooth particle hydrodynamics (SPH) method was used, due to the large deformations that were expected. Using the model, a parametric study on the effects of bird mass and impact energy was performed. The numerical results show that impact damage depends more on impact velocity than the bird mass. In all cases, debonding of the tip of the leading edge was predicted, while for combinations of small bird mass and large impact velocity a more extensive debonding of the protective layer was predicted. Regarding damage in the CFRP, only matrix cracking on the leading edge has been predicted. Aiming to assess the effectiveness of FBGs to detect debonding of the Ti layer due to bird strike, an FBG network has been modeled into the bondline and a study was performed on the correlation of the measured strains with impact damage.