FE Simulation Research Articles

The Effect of the Layup on the Stability of Composite Cylindrical Shells

Fiber reinforced plastic laminated composites have conquered greater and greater territory in the field of engineering in the past decades for their high strength to weight ratio. By varying the layup structure their behavior can easily be modified. One of the applications, that is investigated in this article is the slit tube or cylindrical shell, that used as a structural element undergoes bending. These shells indifferent from their material may experience the snap-through phenomenon (this depends both on the material and geometry) in which the shell flattens and loses its stability to bending. Depending on the layup bistable behavior also can be achieved, i.e., the shell would have two different shapes that are in equilibrium without any constraint. In this article the effect of the layup is investigated both on the bistable behavior and the snap-through phenomenon. Geometric limitations for the bistability are calculated based on a simple beam model from the literature. The same model is used to find the snap-through moment for these shells as a function of the orientation angle. It is also proven that the flattening of the shell cannot be evaded by changing the layup structure. The results are confirmed by FE simulations where applicable.

Reliability-based capacity safety factor for G20Mn5 cast steel joints

Cast steel joints have complex geometries and great load-carrying capacity, and hence their resistances are commonly determined through FE simulations. Considering the significant variability in the material mechanical properties (that in fracture strains, in particular) and the model uncertainty inevitably involved in the FE analysis, a large safety factor (γR) should be adopted for the FE simulation-based design of cast steel joints. However, the γR-values specified by the current design specifications, e.g. the Chinese standard CECS 235: 2008 in which γR = 3.0, are deemed to be overly conservative. This paper examined the structural reliability of G20Mn5 cast steel joints to provide a rational γR-value for the practical joint design. The above-mentioned uncertainty of the material and geometric properties as well as the model uncertainty related to FE simulations are evaluated, and Monte Carlo simulations were conducted on nine representative joints to obtain the statistical characteristics of cast steel joints’ ultimate resistance, allowing for both failure modes of material fracture and instability caused by large-scale yielding. FORM was adopted to calculate the reliability index β for the assumed γR-values and different loading scenarios, and the recommended values for γR under target reliability indices are proposed. For snow load-dominant and wind load-dominant load combinations, the recommended γR corresponding to β = 4.2 are 2.29 and 2.16, respectively, and the recommended γR corresponding to β = 3.7 are 2.01 and 1.90, respectively.

The Influence of Material Properties and Wall Thickness on Predicted Wall Stress in Ascending Aortic Aneurysms: A Finite Element Study.

Finite element analysis (FEA) has been used to predict wall stress in ascending thoracic aortic aneurysm (ATAA) in order to evaluate risk of dissection or rupture. Patient-specific FEA requires detailed information on ATAA geometry, loading conditions, material properties, and wall thickness. Unfortunately, measuring aortic wall thickness and mechanical properties non-invasively poses a significant challenge, necessitating the use of non-patient-specific data in most FE simulations. This study aimed to assess the impact of employing non-patient-specific material properties and wall thickness on ATAA wall stress predictions. FE simulations were performed on 13 ATAA geometries reconstructed from computed tomography angiography (CTA) images. Patient-specific material properties and wall thicknesses were made available from a previous study where uniaxial tensile testing was performed on tissue samples obtained from the same patients. The ATAA wall models were discretised with hexahedral elements and prestressed. For each ATAA model, FE simulations were conducted using patient-specific material properties and wall thicknesses, and group-mean values derived from all tissue samples included in the same experimental study. Literature-based material property and wall thickness were also obtained from the literature and applied to 4 representative cases. Additional FE simulations were performed on these 4 cases by employing group-mean and literature-based wall thicknesses. FE simulations using the group-mean material property produced peak wall stresses comparable to those obtained using patient-specific material properties, with a mean deviation of 7.8%. Peak wall stresses differed by 20.8% and 18.7% in patients with exceptionally stiff or compliant walls, respectively. Comparison to results using literature-based material properties revealed larger discrepancies, ranging from 5.4% to 28.0% (mean 20.1%). Bland-Altman analysis showed significant discrepancies in areas of high wall stress, where wall stress obtained using patient-specific and literature-based properties differed by up to 674kPa, compared to 227kPa between patient-specific and group-mean properties. Regarding wall thickness, using the literature-based value resulted in even larger discrepancies in predicted peak stress, ranging from 24.2% to 30.0% (mean 27.3%). Again, using the group-mean wall thickness offered better predictions with a difference less than 5% in three out of four cases. While peak wall stresses were most affected by the choice of mechanical properties or wall thickness, the overall distribution of wall stress hardly changed. Our study demonstrated the importance of incorporating patient-specific material properties and wall thickness in FEA for risk prediction of aortic dissection or rupture. Our future efforts will focus on developing inverse methods for non-invasive determination of patient-specific wall material parameters and wall thickness.

Predictions of sheet molding compound composite structures using probabilistic finite element simulations with bimodal Weibull strength distributions

Due to the large scatters in Sheet Molding Compound (SMC) mechanical properties, the uncertainty in the prediction of mechanical responses of SMC composite structures is significantly high as compared to that for continuous fiber composite structures. Another challenge is the size effect resulting from the scatter in mechanical strengths, i.e., the measured material flexural strength is much higher than its tensile strength. As a result, classical approaches that rely on the mean tensile strength can substantially underpredict the flexural responses in Finite Element Analysis (FEA). This work investigates the use of a material model with bimodal Weibull distributions for its strength properties in Probabilistic FE (PFE) simulations. A Random Search-based optimization procedure was developed to obtain model parameters which are difficult to determine. The material model was verified by PFE simulations of standard experiments, and then examined in simulations of open-hole tension and disk bending tests.

Bayesian protocols for high-throughput identification of kinematic hardening model forms

Constitutive models are essential for assessing the mechanical response of complex materials, yet uncertainties in model forms and parameters persist due to the influence of micromechanisms and microstructural features. We develop Bayesian protocols to iteratively refine both model forms and the associated material properties for complex constitutive models. Our aim is to provide rigorous, probabilistically informed evaluations of improvements achieved with increasing model complexity. Leveraging high-throughput experimental microindentation data, the protocols involve three steps: (i) emulating FE simulations using multi-output Gaussian process surrogate models, (ii) calibrating an initial simple constitutive model against experimental data, and (iii) progressively enhancing model complexity by iteratively improving agreement between simulations and experiments. The various model forms are compared using model form probabilities and aggregate discrepancies. Sobol indices are used to quantify the identifiability of material properties, aiming to prevent parameter proliferation. We apply this protocol to identify the optimal form of cyclic plasticity models for duplex Ti-6Al-4V. Although tailored for cyclic plasticity models, these protocols hold promise for calibrating and refining nonlinear constitutive models across diverse material classes.

Simulation Research on the Control Method of Bow-Collapse in Gear Cold Roll-Beating

Bow-collapse is a type of geometric defect in the gear cold roll-beating process. In order to effectively control bow-collapse and improve material utilization, this paper calculates the cross-section radius of the blank according to the volume invariance principle of metal plastic deformation, and then performs FE simulation of the cold roll-beating process by using the cyclic beating of adjacent tooth spaces and intermittent blank feeding method. The flow state of metal particles is investigated, revealing that the movement of metal particles along the axial direction of the blank is the main reason for the formation of bow-collapse. This paper proposes a method to correct the cross-section radius of the blank and thus control for bow-collapse, where the loss coefficient K characterizes the state of metal particle loss in an infinitesimal thickness region on the cross-section. The analytical equation for calculating the corrected value of the cross-section radius is derived, and the corrected value is calculated. Conducted on the modified blank, cold roll-beating FE simulation results show that bow-collapse is effectively controlled, and the loss coefficient K correctly reflects the loss state of metal particles on the cross-section. The simulation results also show that after cold roll-beating, the gear teeth with standard face width and tooth depth can be obtained after two turning end faces and turning tip circle processes. The bow-collapse control method proposed in this paper effectively improves material utilization.

Experimental and FE Investigation on the Influence of Impact Load on the Moment Transmission of Smooth Shaft–Hub Connections

A well-known phenomenon in machinery systems is the easing of a blocked connection of mechanical parts after an impact hit close to the connection. Such impact hits may also arise in shaft–hub connections such as gears, crankshafts, or other parts. The objective of this study is to investigate the influence of local impact loads on the transmittable torque of smooth shaft–hub connections. In a specially designed test rig, it was demonstrated that the transmittable torque of the shaft–hub connection is reduced as a consequence of the impact, resulting in a reduction in the frictional force and slippage of the hub. Increasing the impact load leads to an increase in the reduction in the frictional force as well as the slippage and reduces the transmittable torque. By carrying out a modal analysis of the relevant parts and FE simulations of the impact, two possible reasons have been identified: (i) the impact load excites a vibration mode in the connection which reduces the frictional force and the transmittable torque; and (ii) the impact causes local deformation of the shaft, which results in local slip.

An optimal penalty method for the joint stiffening in beam models of additively manufactured lattice structures

Additive manufacturing is revolutionizing structural design, with lattice structures becoming increasingly prominent due to their superior mechanical properties. However, simulating these structures quickly and accurately using the finite element method (FEM) remains challenging. Recent research has highlighted beam element simulation within FEM as a more efficient alternative to traditional solid FE simulations, achieving similar accuracy with reduced computational resources. However, a significant challenge is managing the lack of rigidity at nodes and the prevalence of low aspect ratio beams. While various methodologies have been proposed to address these issues, there is still a gap in the comprehensive evaluation of their limitations. An optimal node penalization methodology is required to expand the limited range of accurately represented lattice behavior. A preliminary study investigates lattice geometries through comparative analysis of solid and beam FE simulations. Built on this, we developed a methodology suitable to linear, dynamics and nonlinear beam FE simulations, contributing to enhanced computational speed and accuracy. Several lattice structures were printed using material jetting and quasi-static compressive tests were conducted to validate the methodology’s accuracy. The numerical results reveal a good accuracy between the proposed beam FE methodology and the experimental data, offering a better alternative to conventional FEM for energy absorption in terms of computing time.

Mechanical and failure behaviors of adhesively bonded dissimilar materials joints incorporating bio-inspired morphological irregularities

Adhesive dissimilar material joints between stainless steel grade 316L and polyethylene terephthalate glycol (PETG) plastic were examined, in which irregular interface morphologies inspired by natural sutures were incorporated. The joint interfaces exhibited various teeth-like, non-repetitive zigzag patterns based on a pseudo-randomization method and sutural interdigitation index. Effects of their irregularities on mechanical and failure characteristics of adhesive butt joints were studied by means of experiments and FE simulations. The cohesive zone model, Drucker-Prager plasticity model and ductile failure criterion were applied for the interface and PETG, respectively. Predicted load-displacement curves of joints with different teeth profiles were well validated. The degree of irregularity became higher to 20%, 40%, and 60%, the joint strengths decreased by 1.47%, 5.39%, and 11.95%, while the total energies to failure increased by 110.74%, 129.33%, and 161.23%, accordingly. More inhomogeneous morphologies led to earlier local damage initiation, but enhanced damage evolution range by impeding abrupt joint separation. Smaller teeth angles provided higher joint strength, whereas significant declines of bonding strength were observed by too acute teeth angle due to excessive stress localization and resulting teeth breakage. The teeth angle of 45º enabled the superior joint performance owing to a proper combination of interlocking and large adhesive force under shear stress state. Finally, a key insight for designing an optimal dissimilar joint with morphological irregularities was provided.

Nonlinear mechanics of horseshoe microstructure-based lattice design

Enhancing buffering capacity, flexibility, and energy absorption to withstand large deformations in structure remains a challenge. Bio-inspired horseshoe lattice structures, with their curved trusses, exhibit distinct mechanical characteristics compared to conventional metamaterials. However, their mechanical properties under in-plane compression have been rarely explored. This study characterised and modelled three types of novel 3D-printed horseshoe lattice structures, totalling 12 configurations, with unit cell geometry varying based on cell-wall angles ranging from 120°to 210°. The implementation of the FE simulation based on the three-network viscoplastic (TNV) model showed good agreement with the experiments. The results demonstrated that the cell-wall angle in the geometry and the cross-lap joint topology were significantly associated with the failure mechanism of the unit cell and the overall non-linear mechanical behaviour. Increasing the cell-wall angles can prevent beams from failing due to bending and buckling fractures, facilitate the initiation of internal contacts and stretching during in-plane compression. This reveals a configurable mechanism where the flexibility and stability of the lattice structure can trigger strain hardening, resulting in an increase in load-bearing capacity. The sensitivity to strain hardening varies depending on the order of cross-laps within the topology. A colour-pattern tracking method was employed to monitor the progressive stabilisation of lattice structures, and offering a novel approach for the future design of flexible, configurable, and programmable horseshoe-based lattice structures.

Damage of thin target plates impacted by conical projectiles with varying apex angles in ballistic application: experimental, FEA and ANN integrated approach

In the current study, an experimental setup consisting of smoothbore 30-caliber powder gun was employed to launch spherical projectiles (3 g/ϕ9) in the ballistic range of velocities from 500 to 1700 m/s and obliquity (0, 33 and 65°), impacting 2 mm thin Steel 1006 target plates. Crater dimensions (major and minor dia.) obtained from series of FE simulations run for the above configuaration was validated by corresponding experimental data. Subsequently, a fullscale 3D FE model considering 8-noded hexahedral elements was used to discretize SS304 conical projectiles (replacing spherical projectile) with various apex angles viz. 40°, 60°, 80° and 100° impacting on single (3 mm) and double layer (1.5 mm each) steel 1006 targets (replacing 2 mm target) in LS dyna. The material behavior was characterized using J–C strength and damage models, along with Gruneisen Equation of State. An erosion algorithm was used in the explicit FE code LS-DYNA to remove undesirable elements. In the next stage, Adam and Nadam optimizers have been employed in ANN models developed using Python code within the Tensor-Flow framework. The Keras Tuner library in the Tensor-Flow framework was used for hyper parameter tuning. The ANN models trained using simulation data successfully predicted the residual KE of conical projectiles with intermediate apex angles of 90°, 70°, and 50° across twelve different impact scenarios. The models with Adam and Nadam optimizers achieved mean squared error (MSE)/coefficient of determination (R2)/mean absolute percentage error (MAPE) values of 109.44/0.998/6.72 and 91.19/0.998/7.76, respectively.

A semi-analytical method based on the Green's function for the laser melting process of the metal materials

Thermal responses of the metal materials subjected to intense laser irradiation are complicated due to the phase change in the melting process. In order to simplify this problem, previous studies usually ignored the liquid phase or took the usage of finite element method, which limited the achievement of theoretical breakthroughs. In the present study, a one-dimensional heat transfer model with consideration of phase change was established to describe the melting process of the metal materials caused by a constant intense laser beam. The governing equations with three domains were constructed in the piecewise form: the liquid phase region (melted already), the solid phase region (unmelted yet) and the melting region. The limited discretization method was employed to describe the moving of the soli-liquid interface and the energy exchange. The piecewise governing equations in liquid and solid region were solved separately and analytically by means of the Green's function method, and the calculation result was verified by the finite element simulation. The results of the analytical model were in good agreement with those of the finite element simulation, and the maximal prediction errors of the temperature field prediction between the theoretical model and FE simulation is limited to 2.8 %. In addition, the influences of heat source intensity, material heat conductivity, latent heat on the melting process were discussed in detail. The analytical and simulation results reveal that the semi-analytical solution in piecewise for 1-D laser melting process can be successfully used to reflect the dynamic temperature response of the metal materials and the movement of the solid-liquid interface. This work is of guiding significance for the analytical solution of the multi-dimensional melting process of the metal materials under the fixed and continuous laser beams.

Experimental and numerical analysis of ballistic impat and material characterization of GFRP and Kevlar 29/epoxy composite laminate

Through experimental testing and numerical simulations, this study examines the effects of ballistic events on thin FRP composite laminated plates fabricated using a hand lay-up method. Experimental ballistic impact tests using a pneumatic gun are conducted on composite plates reinforced with woven glass and woven Kevlar 29 fibers. An advanced three-dimensional finite element model programed in Ansys/Autodyn v19.1 is employed to verify the experimental findings and analyze the ballistic perforation characteristics of the target. The crucial material constants needed for the constitutive material model used in the simulation are acquired through precise experimentation on samples prepared from the fabricated laminates. Significant agreement is observed between the FE simulations and experimental findings, particularly concerning the assessment of residual velocities of the projectile and damage pattern in the laminates. The results of this study show that when subjected to ballistic impact by a flat-ended cylindrical projectile, the thin woven FRP composite primarily experiences damage characterized by delamination, fiber breakage and matrix cracking. Additionally, based on current simulations, it is observed that the ballistic limit velocity of the Kevlar 29/epoxy laminate exceeds that of GFRP by 25.64% when both materials have an equal thickness of 2.8 mm.

The Designs and Testing of Biodegradable Energy-Absorbing Inserts for Enhanced Crashworthiness in Sports Helmets.

This article addresses manufacturing structures made via injection molding from biodegradable materials. The mentioned structures can be successfully used as energy-absorbing liners of all kinds of sports helmets, replacing the previously used expanded polystyrene. This paper is focused on injection technological tests and tensile tests (in quasi-static and dynamic conditions) of several composites based on a PLA matrix with the addition of other biodegradable softening agents, such as PBAT and TPS (the blends were prepared via melt blending using a screw extruder with mass compositions of 50:50, 30:70, and 15:85). Tensile tests showed a positive strain rate sensitivity of the mixtures and a dependence of the increase in the ratio of the dynamic to static yield stress on the increase in the share of the plastic component in the mixture. Technological tests showed that increasing the amount of the plasticizing additive by 35% (from 50% to 85%) results in a decrease in the minimal thickness of the thin-walled element that can be successfully injection molded by about 32% in the case of PLA/PBAT blends (from 0.22 mm to 0.15 mm) and by about 26% in the case of PLA/TPS blends (from 0.23 mm to 0.17 mm). Next, the thin-walled elements (dimensions of 55 × 55 × 20 mm) were manufactured and evaluated using a spring-loaded drop hammer. The 60 J impact energy was tested in accordance with the EN 1078 standard. The dynamic crushing test included checking the influence of the materials' temperature (-20, 0, 20, and 40 °C) and the impact velocity. It was proven that the maximum deflection increases with increasing material temperature and an increase in the share of the plastic component in the mixture. The PLA15PBAT85 blend was selected as the most effective material in terms of its use as an energy-absorbing liner for sport helmets. Johnson-Cook and Cowper-Symonds material plasticizing models were constructed. Their use during dynamic FE simulation provided results that were in good agreement with those of the conducted experiment.

Study on characterization of moderate energy impact response of elastic-plastic plate structure

This paper presents a study on the characterization of the moderate energy impact response between the elastic-plastic plate and the elastic-plastic sphere. An equivalent contact stiffness is proposed to substitute the linear contact stiffness, and a universal analytical expression is presented according to the intensive FE simulations for different material combinations under moderate impact energy. Then, a modified characterization diagram is suggested using the analytical expression. The modified diagram is validated by the FE simulations and experimental results. The results show the modified diagram can predict the maximum impact force and the response type in a fast and simple way.

A new multi-DOF envelope forming process for fabricating spiral bevel gears with back taper tooth

Spiral bevel gears are critical transmission components, and are widely used in the aerospace field. This paper proposes a new multi-DOF envelope forming process for fabricating spiral bevel gears. Firstly, the multi-DOF envelope forming principle of spiral bevel gears is proposed. Secondly, the design methods for the envelope tool geometry and movement are proposed based on the envelope geometry and movement relationships. Thirdly, the metal flow and tooth filling laws are revealed through 3D FE simulation of the multi-DOF envelope forming process of a typical spiral bevel gear. Fourthly, a new method for separating the envelope tool and the formed spiral bevel gear with back taper tooth is proposed to avoid their interference. Finally, experiments on multi-DOF envelope forming of this typical spiral bevel gear are conducted using new heavy load multi-DOF envelope forming equipment. The simulation and experimental results show the feasibility of the proposed multi-DOF envelope forming process for fabricating spiral bevel gears with back taper tooth and the corresponding process design methods.

Tire Design Using FE Simulation and Multi-Objective Optimization

Tire Design Using FE Simulation and Multi-Objective Optimization

Application of Numerical Modeling and Finite Element Analysis in Fused Filament Fabrication: A Review.

Additive manufacturing (AM) is not necessarily a new process but an advanced method for manufacturing complex three-dimensional (3D) parts. Among the several advantages of AM are the affordable cost, capability of building objects with complex structures for small-batch production, and raw material versatility. There are several sub-categories of AM, among which is fused filament fabrication (FFF), also commonly known as fused deposition modeling (FDM). FFF has been one of the most widely used additive manufacturing techniques due to its cost-efficiency, simplicity, and widespread availability. The FFF process is mainly used to create 3D parts made of thermoplastic polymers, and complex physical phenomena such as melt flow, heat transfer, solidification, crystallization, etc. are involved in the FFF process. Different techniques have been developed and employed to analyze these phenomena, including experimental, analytical, numerical, and finite element analysis (FEA). This study specifically aims to provide a comprehensive review of the developed numerical models and simulation tools used to analyze melt flow behavior, heat transfer, crystallization and solidification kinetics, structural analysis, and the material characterization of polymeric components in the FFF process. The strengths and weaknesses of these numerical models are discussed, simplifications and assumptions are highlighted, and an outlook on future work in the numerical modeling and FE simulation of FFF is provided.

Extension of a Contact Subroutine for Composite Ring Rolling to Include Temperature Dependency

By combining the ring rolling and roll bonding processes, the product spectrum can be additionally expanded. Since a successful composite ring rolling process requires a higher growth tendency for the inner ring, previous publications commonly included a softer inner ring to reduce the flow resistance of the inner ring or specific geometries for rings and tools. In this work, the material combination of a 100Cr6 (DIN 1.3505, AISI 52100) outer ring and a 42CrMo4 (DIN 1.7225, AISI 4140) inner ring is used to show that the composite ring rolling process is also possible for material combinations with a balanced flow stress ratio and equal wall thicknesses. In earlier publications, the influence of temperature was neglected. As the influence on the yield stress and thus on the success of the process has a significant influence, this should be considered in order to be able to make a reliable statement. For this purpose, the bond formation of the two materials was investigated by bonding experiments, and an existing bond formation model was extended with respect to the temperature dependency. On the basis of this model, the process control parameters were investigated using FE simulations, and a ring rolling experiment was carried out.

Study on microstructure characterization of steel using on multi-frequency electromagnetic detection and FE simulation calculation

Microstructures dominate mechanical properties of steel materials. Monitoring and controlling microstructure variations are important for high-quality steel productions. In this study, the multi-frequency electromagnetic technology is used to effectively characterize changes of steel microstructures. Steel samples with individual micro- components are obtained using different heat treatments and are measured using a self-designed multi-frequency electromagnetic system. Micro- and Macro- FE models are developed to discuss electromagnetic responses on steel microstructures with different phases, grain size and grain boundaries. The relative permeability of different steel microstructures are calculated and discussed. Results show that the low frequency inductance will increase with the increase of ferrite grain size and ferrite fraction. The relative permeability of single ferrite grain boundary is determined to be 165 and the orientation of grain boundary can influence the relative permeability of steel microstructures.