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The heat transfer coefficient, including interfacial heat transfer coefficient (IHTC) and convective heat transfer coefficient (CHTC), plays a pivotal role in the thermal dynamics of hot gas forming processes. This parameter can determine the temperature field, thereby affecting the deformation and mechanical properties of the material to improve productivity. In this paper, we present an innovative experimental apparatus designed to measure the temperature evolutions of the aluminum specimen and the die during the hot gas forming processes. This apparatus is capable of simultaneously measuring IHTC and CHTC. Using the inverse finite element method, the simulated temperature histories are matched with empirical data and the best-fit values are adopted as indicative of IHTC and CHTC. This study identified the effects of contact pressure and die temperature on IHTC, as well as the impact of gas pressure on CHTC. In addition, a predictive model was developed to forecast the IHTC and CHTC at varying contact pressures and die temperatures with a prediction accuracy surpassing 0.95. By leveraging the predictive model presented in this paper, users can modulate contact pressure and die temperature based on specific production needs to achieve a targeted temperature profile. This method offers enhanced precision in managing the temperature field of the workpiece during hot gas forming experiments, thereby refining the temperature distribution. Moreover, it optimizes the formability and microstructural attributes of the material, ultimately leading to improved mechanical characteristics. [ABSTRACT FROM AUTHOR]

Metal/CFRP hybrid structures have been increasingly applied in the automotive industry due to their favorable weight-saving and crashworthiness. In this article, a nonlinear finite element (FE) model is established to study the axial crushing behavior of aluminum/CFRP thin-walled tube structures. A progressive damage constitutive model is employed to capture the intra-laminar response of composites; Johnson-Cook model is used to describe the crushing process of aluminum layers and a bilinear cohesive zone model is applied for modeling the inter-layer delamination during the collapse process. A user material subroutine VUMAT involving these damage models is coded and executed to attain the numerical solution based on ABAQUS/Explicit solver. The axial crushing processes of thin-walled tubes with different configurations are simulated, and the corresponding damage characteristics are analyzed thoroughly. The influence of aluminum layer arrangement and cross-sectional shape on the crashworthiness and energy absorption of thin-walled tubes is discussed, which provides a design basis for the application of energy absorption elements. [ABSTRACT FROM AUTHOR]

Featured Application: Safety calculation for 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. [ABSTRACT FROM AUTHOR]

Highlights Glass fiber reinforced plastics (GFRPs) is a key material for the outer protecting layer of ships as well as for energy storage tanks. Its ballistic and blast resistance is closely related to the inclusion structure of its glass fiber and polyester matrix, however, the related detailed studies have not been reported. In this paper, ballistic shooting tests and finite element simulations are both employed to investigate the ballistic limit velocities (V50) of GFRPs and reveal the effects of glass fiber layers and the polyester matrix thickness on the V50. The results show that the V50 of GFRPs is essentially linearly related to the thickness of the target plate for a given number of glass fiber layers. An increase in the number of glass fiber layers enhances the overall V50 value of GFRPs, but the linear relationship with the thickness remains unchanged. The target plate with more layers of glass fiber interacts with the projectile for a longer time, resulting in the debonding of the fiber and the resin matrix. The resin around the crater loses its support and then produces irregular cracks. Based on energy conservation, a theoretical model for predicting the V50 of GFRPs with considering the effects of glass fiber and polyester matrix is proposed. After comparing the results of theoretical calculations with experimental and simulation data, the relationship equations between the key parameters (ballistic strength) in the model and the number of fiber layers and target plate thickness are finally given. These findings can provide support for the design of ballistic GFRPs. Ballistic velocity limit (V50) of glass fiber reinforced plastics (GFRPs) obtained by experiment and finite element simulation Tuning the V50 of GFRPs by designing the number of glass fiber and polyester thickness. Proposed a theoretical model for predicting the V50 of GFRPs. [ABSTRACT FROM AUTHOR]

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 rollbeating, 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. [ABSTRACT FROM AUTHOR]

Local post-weld heat treatment (PWHT) is the only option for heat treating field welded joints. Quite often, the success of local PWHT in alleviating the residual stress and tempering the material within the soak band (SB) is dependent on the ability to achieve the required heat treatment temperature and maintain through-thickness temperature gradient (TTG) within the specified limits at the end of heating cycle, whence soaking begins. Field observations reveal the inadequacy of AWS D 10.10 specified parameters viz. rate of heating (ROH), heat band (HB) and insulation band width in not achieving the required TTG for certain pipe dimensions. Although prior works have attempted to address this issue by widening the HB, the capacity of the heating equipment often pose a limitation. In such cases, reducing ROH is a plausible alternative. With, no such prior studies seen in literature, an exhaustive finite-element analysis simulating the local PWHT on 81, SA106GrC pipe samples (diameter and thickness varied in 9 levels each) was performed, thrice. First as per AWS recommendations, second by halving the code deduced ROH and third by doubling the code deduced HB. The trend of important outcomes (TTG, power source rating and energy consumption) with great significance to the heat treatment industry were also compared and analysed. Two nomograms were developed to serve as a ready reckoner for field heat treater in not only assessing the adequacy of heat treatment parameters but also with possible alternatives in achieving the desired TTG using field-available power source. [ABSTRACT FROM AUTHOR]

Directed energy deposition-laser beam/powder (DED-LB/Powder) is an additive manufacturing process that is gaining popularity in the manufacturing industry due to its numerous advantages, particularly in repairing operations. However, its application is often limited to case studies due to some critical issues that need to be addressed, such as the degree of internal porosity. This paper investigates the effect of the most relevant process parameters of the DED-LB/Powder process on the level and distribution of porosity. Results indicate that, among the process parameters examined, porosity is less affected by travel speed and more influenced by powder mass flow rate and laser power. Additionally, a three-dimensional finite element transient model was introduced, which was able to predict the development and location of lack-of-fusion pores along the building direction. [ABSTRACT FROM AUTHOR]

Die-less spinning is developed because of its advantages of low cost and high flexibility. The spherical roller has not been commonly used in the die-less spinning process. In previous studies, the sizes of the spherical rollers are varied, and the distributions of the wall thickness of the formed parts are inconsistent. To explore the effects of spherical roller dimensions on the formed parts, four spherical rollers of different radii are adopted to form the truncated cone-shaped parts. Meanwhile, the finite element models are established to analyze the stress states during the spinning process. The wall thickness distribution and the outer contour accuracy of the experimental parts are measured. Combined with the finite element simulation results, it is found that the curvature of the roller and the contact area between the roller and the sheet has an important influence on the wall thickness distribution and outer contour accuracy of the parts. In addition, the too-small radius of the roller makes the shear stress on the sheet material greatly increase. It results in the wall consistent with the sin law of die-less shear spinning. [ABSTRACT FROM AUTHOR]

A combined stamping–bulging forming process was proposed to achieve high-precision forming of large-diameter, ultra-thin-walled, superalloy welded S-type corrugated diaphragms. The underlying principle is to enhance the diaphragm's forming accuracy by increasing the plastic deformation region and reducing springback. Using the ABAQUS version 6.14 finite element analysis software, finite element models were constructed for the stamping, hydraulic bulging, and combined stamping–bulging forming processes of the welded S-type metal corrugated diaphragms. A comparative analysis was conducted on the forming processes of the welded S-type metal corrugated diaphragms under the three forming methods, focusing on equivalent stress, distribution of wall thickness, and forming accuracy. This analysis determined the optimal forming process and the corresponding process parameters for superalloy welded S-type metal corrugated diaphragms. The results show that under a constant drawing force, as the bulging pressure increases, the plastic deformation of the straight sections of the diaphragm becomes more pronounced, resulting in improved shape accuracy. The combined stamping–bulging forming process guarantees the highest degree of shape accuracy for the diaphragm. The optimal process parameters were identified as a 30 t force and a 5 MPa pressure, with a maximum shape error of 0.02 mm. Concerning a plate thickness of 0.3 mm, the maximum deviation rate was found to be 6.7%, which represents a 30% improvement over traditional stamping processes. The maximum wall thinning rate was found to be 3.3%, a 1% reduction compared to traditional stamping processes, confirming the process's feasibility. [ABSTRACT FROM AUTHOR]

Homogeneous polynomial functions have the potential to provide a general modeling framework for yield surfaces in metal plasticity. They incorporate as particular cases many of the previously proposed yield functions and their fitting capabilities allow for capturing a wide range of yield surface shapes. And yet, there are still two unsolved problems which turn into major obstacles when it comes to actual implementations in both academic and industrial environments: The lack of a general optimization algorithm for the calibration of their parameters and the lack of an efficient computational scheme for their value, gradient and hessian. The difficulty of the first problem is two-fold, necessitating an adequate specification of the experimental input data set and satisfaction of the convexity constraint. The second problem is specific to all high degree polynomials and is comprised of issues such as numerical stability, precision and implementation efficiency. We present practical solutions to both problems: An optimization algorithm that reduces to solving a sequence of quadratic problems and a double Horner evaluation scheme that is optimal (featuring the least number of multiplications). The resulting modeling framework can account for arbitrary input data, experimental or from crystal plasticity predictions. As illustration we show new results regarding the relationship between generalized r-values and the earing profile of deep-drawn cylindrical cups. Practicality is demonstrated by the high level of automation of the entire workflow, from material parameters calibration to finite element simulations, and supporting code (Python scripts and constitutive subroutine) made available at https://github.com/stefanSCS/PolyN. [ABSTRACT FROM AUTHOR]

Purpose: The research aims to investigate the impact of thermo-mechanical aging on SBR under cyclic-loading. By conducting experimental analyses and developing a 3D finite element analysis (FEA) model, it seeks to understand chemical and physical changes during aging processes. This research provides insights into nonlinear mechanical behavior, stress softening and microstructural alterations in SBR compounds, improving material performance and guiding future strategies. Design/methodology/approach: This study combines experimental analyses, including cyclic tensile loading, attenuated total reflection (ATR), spectroscopy and energy-dispersive X-ray spectroscopy (EDS) line scans, to investigate the effects of thermo-mechanical aging (TMA) on carbon-black (CB) reinforced styrene-butadiene rubber (SBR). It employs a 3D FEA model using the Abaqus/Implicit code to comprehend the nonlinear behavior and stress softening response, offering a holistic understanding of aging processes and mechanical behavior under cyclic-loading. Findings: This study reveals significant insights into SBR behavior during thermo-mechanical aging. Findings include surface roughness variations, chemical alterations and microstructural changes. Notably, a partial recovery of stiffness was observed as a function of CB volume fraction. The developed 3D FEA model accurately depicts nonlinear behavior, stress softening and strain fields around CB particles in unstressed states, predicting hysteresis and energy dissipation in aged SBRs. Originality/value: This research offers novel insights by comprehensively investigating the impact of thermo-mechanical aging on CB-reinforced-SBR. The fusion of experimental techniques with FEA simulations reveals time-dependent mechanical behavior and microstructural changes in SBR materials. The model serves as a valuable tool for predicting material responses under various conditions, advancing the design and engineering of SBR-based products across industries. [ABSTRACT FROM AUTHOR]

Large-dimension complex integral thin-shell components are widely used in advanced transportation equipment. However, with the dimensional limitations of raw blanks and the manufacturing process, there are inhomogeneous geometric and mechanical properties at welded joints after welding, which have a significant effect on the subsequent forming process. Therefore, in this paper, the microstructure of welded joints with a sharp property change was accurately characterized by the proposed isothermal treatment method using the BR1500HS welded tube as an example. In addition, an accurate constitutive model of welded tubes was established to predict the deformation behavior. Firstly, the heat-treated specimens were subjected to uniaxial tensile tests and the stress–strain curves under different heat treatment conditions were obtained. Then, the continuous change in flow stress in the direction of the base metal zone, the heat-affected zone and the weld zone was described by the relationship between the microhardness, flow stress and center angle of the welded tube. Using such a method, a continuous constitutive model of welded tubes has been established. Finally, the constitutive model was compiled into finite-element software as a user material subroutine (VUHARD). The reliability of the established constitutive model was verified by simulating the free hydro-bulging process of welded tubes. The results indicated that the continuous constitutive model can well describe the deformation response during the free hydro-bulging process, and accurately predicted the equivalent strain distribution and thickness thinning rate. This study provides guidance in accurately predicting the plastic deformation behavior of welded tubes and its application in practice in hydroforming industries. [ABSTRACT FROM AUTHOR]

The reconstruction of the spatial complex conductivity σ + j ω ε 0 ε r from complex valued impedance measurements forms the inverse problem of complex electrical impedance tomography or complex electrical capacitance tomography. Regularized Gauß-Newton schemes have been proposed for their solution. However, the necessary computation of the Jacobian is known to be computationally expensive, as standard techniques such as adjoint field methods require additional simulations. In this work, we show a more efficient way to computationally access the Jacobian matrix. In particular, the presented techniques do not require additional simulations, making the use of the Jacobian, free of additional computational costs. [ABSTRACT FROM AUTHOR]

A buckling defect will appear on the outer surface of the deformed ring during the constrained ring rolling (CRR) of an aluminum alloy thin-wall conical ring with inner high ribs (AATWCRIHR) if the geometrical dimension of the ribs does not match the wall thickness. To avoid the buckling defect, a quantitative method for characterizing the degree of the buckling defect is proposed using the area of the buckling profile. Then, an orthogonal experimental scheme was designed, taking the width of the middle rib, thickness of wall, and height of the middle rib as the design variables and defining the area of the buckling profile as the optimization objective. Subsequently, a quadratic polynomial response surface model was established by combining the optimization algorithm with the finite element method (FEM), and the geometrical dimension of the middle ribs of the deformed AATWCRIHR is optimized. Moreover, the optimal parameter combination to minimize the area of the buckling profile is obtained and verified using FE simulation. The results show that the AATWCRIHR after optimization does not generate the buckling defect during constrained ring rolling, and it is proven that the quantitative buckling defect representation method and the optimization design method based on the response surface model and the finite element simulation results are feasible for the constrained ring-rolling process of the AATWCRIHR. [ABSTRACT FROM AUTHOR]

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.

As a result of conventional wire-forming processes, the residual stress distribution in wires is frequently unfavorable for subsequent forming processes such as bending operations. High tensile residual stresses typically occur in the near-surface region of the wires and can limit further application and processability of the semi-finished products. This paper presents an approach for tailoring the residual stress distribution by modifying the forming process, especially with regard to the die geometry and the influence of the drawing velocity as well as the wire temperature. The aim is to mitigate the near-surface tensile residual stresses induced by the drawing process. Preliminary studies have shown that modifications in the forming zone of the dies have a significant impact on the plastic strain and deformation direction, and the approach can be applied to effectively reduce the process-induced near-surface residual stress distributions without affecting the diameter of the product geometry. In this first approach, the process variant using three different drawing die geometries was established for the metastable austenitic stainless steel X5CrNi18-10 (1.4301) using slow (20 mm/s) and fast (2000 mm/s) drawing velocities. The residual stress depth distributions were determined by means of incremental hole drilling. Complementary X-ray stress analysis was carried out to analyze the phase-specific residual stresses since strain-induced martensitic transformations occurred close to the surface as a consequence of the shear deformation and the frictional loading. This paper describes the setup of the drawing tools as well as the results of the experimental tests. [ABSTRACT FROM AUTHOR]

Buckling behavior of laminated composites are entirely depends on the geometry and stacking sequence of layers. The different fiber paths as a result of the stacking sequence can affect the buckling properties of laminates. The aim of this paper is to determine the effect of fiber path on the buckling behavior of laminated composites using Yarn Interlacing Matrix (YIM). Different fiber paths were implemented by making hybrid/uniform laminates. Glass woven fabrics with different yarn architectures and epoxy resin were used to fabricate the 8-plies laminated composites in 25 × 25 cm2 with 25 × 8.5 cm2 aluminum sheet in middle layer by vacuum infusion process (VIP). The buckling test was carried out on the prepared samples using DARTEC testing machine with five replicates. In addition, the buckling behavior of laminates was simulated using ABAQUS software. The novelty of this study is to use the YIM in theoretical model and investigate the critical buckling load of hybrid laminate composite in pattern of weave and understand the effect of geometrical hybridization on critical buckling load. It showed that the critical buckling load for hybrid samples are larger than the uniform ones. Comparison between theoretical and experimental results of the critical buckling load showed a maximum error of 16% in predicting the critical buckling loads. Also, comparison between theoretical and experimental results of the critical buckling load showed a maximum error of 59.7% in predicting the critical buckling loads. The main outcome of this research is that the fiber path has a greater effect on the buckling behavior than the elastic modulus of the laminates; so that despite the lower elastic modulus, the critical buckling load of laminates with hybrid reinforcement is higher than that of laminates with uniform reinforcements. [ABSTRACT FROM AUTHOR]

A new manufacturing process has been developed that involves drawing circular sheets of thin metal through a conical die to create square cups. This technique produces deep square cups with a height-to-punch-side length ratio of approximately 2, as well as high dimensional accuracy and a nearly uniform height. The study investigated how various factors, including the sheet material properties and process geometric parameters, affect the limiting drawing ratio (LDR). The researchers used finite element analysis to determine the optimal die design for achieving a high LDR and found that the proposed technique is advantageous for producing long square cups with high dimensional accuracy. [ABSTRACT FROM AUTHOR]

In this work, a novel five-step cold extrusion forging technology was proposed for fabricating a shaped charge liner with hyperboloid structure feature, in which three steps forming to develop the macroscopic hyperboloid shape and two steps annealing treatments to improve the microstructure and property of the liner. Besides, the preforming process was the focus of this investigation because the size structure, microstructure, and texture of the preform play a crucial role in the manufacture of the final forming process due to the heredity of dimension and microstructure, which also provides powerful process reference with the following forming steps. Based on the ABAQUS finite element (FE) platform, the cold extrusion process of the shaped charge liner preform was simulated, and the influences of forming parameters such as the initial billet size and friction coefficient between billet and dies on forming load, cavity filling, and strain distribution of the preform were investigated, respectively. The simulation results show that the optimal parameters of initial billet diameter and friction coefficient between dies and billet in cold extrusion preforming of shaped charge liner are 50 mm and 0.1, respectively. Additionally, the strain distribution of the shaped charge liner in the cold forming process was analyzed in detail. Finally, the experiment of the cold extrusion of the shaped charge liner preform was carried out to verify the feasibility of the cold extrusion process and the correctness of the simulation results. [ABSTRACT FROM AUTHOR]

The profile rings with outer groove are widely used in advanced technological fields. To improve the filling accuracy of the cross-section profile of profile ring with outer groove, the deformation behaviors and filling features of the ring are explored. The deformation coefficient of the cross-section profile per revolution for profile ring with outer groove rolling process is introduced, and the change law of the deformation coefficient of the cross-section profile per revolution for profile ring with outer groove under different influencing factors is revealed. And then, the mathematical model of the deformation coefficient of the cross-section profile per revolution for profile ring with outer groove is established. Then, a prediction model of the ultimate forming dimension for profile ring with outer groove rolling process is proposed, and the specific application of the ultimate forming dimension model is clarified. Finally, the target forged ring of the profile ring with outer groove is designed to verify the ultimate forming dimension model by simulation and experiment. The results show that the prediction model can predict the rolling size of the profile ring with outer groove well. This study can provide a guide for the design and optimization of ring forgings with outer grooves in industrial production. [ABSTRACT FROM AUTHOR]

Superior ballistic performance and the lightweight character of Ti alloys are considered as main reasons for their use in armour applications against a broad spectrum of ballistic threats, e.g. bullet, fragment or blast impact. Because dynamic loading caused by typical penetrators is characterized by high strain rates, only specific test methods allow a closer investigation of the respective material behaviour. In the present study, quasi-static and dynamic compression tests as well as ballistic tests were conducted on a two-phase α+β alloy Ti-6Al-4V (in m%) manufactured by hot-rolling. Post-deformation heat treatments, influencing microstructure and mechanical properties were applied in order to compare three different microstructural configurations: as-rolled, mill-annealed and bimodal. While, on the one hand, ballistic tests were employed for the determination of the ballistic limit velocity v50, compression tests, on the other hand, delivered essential input parameters for the application of the Johnson-Cook constitutive model in a finite element simulation of the impact event. The comparison of experimental results to simulation results was supplemented by means of microstructural characterization of tested samples with the focus set on the prevalently observed deformation and damage mechanisms, as for example adiabatic shearing.

During bone drilling surgery, the bone drill can generate drilling force and frictional heat, which may lead to mechanical and thermal damage to the bone tissue. This paper presents a finite element (FE) simulation of bone drilling for cortical and cancellous bone, analyzing the influence of drilling parameters on bone drilling force and temperature. The simulation results reveal the change laws of axial force and temperature during different density bone drilling for various parameters. To optimize the bone drilling parameters, the Taguchi method is applied to conduct bone drilling simulation experiments based on the FE simulation model. The optimal values of axial force and temperature are predicted and calculated under the condition of optimal drilling parameters. Furthermore, a robot bone drilling experiment platform is used to verify the bone drilling FE simulation model and the optimal parameters. The research demonstrates that the FE simulation model effectively explores the influence of drilling parameters on bone drilling force and temperature, while the Taguchi method optimizes the drill parameters to minimize the mechanical and thermal damage to the bone tissue.

We have developed a new design for a photoacoustic (PA) cell particularly suited for quartz-enhanced photoacoustic spectroscopy (QEPAS), where a quartz tuning fork (QTF) is used as a sound detector for the PA signal. The cell is designed for the investigation of solid and semi-solid samples and represents a unilateral open cylinder. The antinode of the sound pressure of the fundamental longitudinal mode of the half-open cylinder occurs directly at the sample, where a measurement is difficult. Therefore, the first harmonic is used. A small hole in the resonator wall at the location of the pressure antinode allows signal detection outside the cylinder without (or only minimally) changing the resonance conditions. This design is particularly simple and easy to manufacture. A finite element (FE) simulation is applied to determine the optimal cell length for the given frequency and the location of the pressure maximum. One difficulty is that the open end dramatically changes the acoustic sound field. We answer the following research questions: where is the sound pressure maximum located and do simple analytical equations agree with the results of the FE simulation? [ABSTRACT FROM AUTHOR]

The mechanical behavior of steel–concrete–steel (SCS) sandwich composite structures under low- or high-velocity impact loading has garnered increasing attention from researchers in recent decades. However, to date, limited effort has been dedicated to studying the residual resistance of SCS sandwich composite structures following impact damage. In a previous investigation, the authors developed a rubberized lightweight high-ductility cement composite (RLHDC) for implementation in double-layer steel–RLHDC–steel composite panels and examined the dynamic response of these panels under impact. To further explore the residual performance of impact-damaged composite panels, the present study conducts flexural tests on nine such panels. The study quantifies and analyzes the effects of various connector types, connector spacing, number of concrete layers, rubber powder content, and number of impacts on the residual flexural resistance of the impact-damaged composite panels. Detailed analysis is conducted on the failure modes, load–displacement curves, strain curves, and load–slip curves of the impact-damaged specimens. The test results reveal that the impact-damaged composite panels experience flexural failure with bond slip under static load. The residual flexural performance is found to be sensitive to the number of concrete layers and number of impacts. Finite element (FE) simulations are performed using LS-DYNA to investigate the residual flexural behavior of the impact-damaged composite panels. The restart method is employed in the simulations to mimic the post-impact static loading scenario. The agreement between the FE results and the experimental findings validates the model and provides a straightforward and effective approach for studying the residual performance of composite structures. An expanded parameter analysis leveraging the calibrated FE model indicates that the steel plate's thickness and strength predominantly influence the composite panel's residual resistance, whereas the influence from concrete strength proves less consequential. [ABSTRACT FROM AUTHOR]

Understanding the microscopic damage process of Al2O3 particle-reinforced stainless steel composite coatings under impact loading is vital for the design of impact-resistant coatings, but also complex and challenging due to their inferior toughness. In this work, the stress/strain fields and coating cracks of HVAF-sprayed monolayer and Al2O3 particle (two different sizes)-reinforced stainless steel composite coatings under falling ball impact were analyzed by means of finite element simulation and experimental verification. The results showed that three types of cracks, including circular cracks, cone cracks and radial cracks, were generated in the coating during impact, which were mainly induced by the tensile stress at the edge of the impact crater, the shear stress inside the coating, and the equivalent plastic strain on the interface of the coating/substrate, respectively. Compared to the monolayer coating, the stress concentration of the composite coating under impact was dispersed by the Al2O3 particles (mainly around the particles). The crack propagation was hampered and deflected by the interface between the particles and the matrix, and the particle fracture would dissipate the impact energy. It was also found that the stress amplitude around the larger Al2O3 particles was smaller and the probability of crack initiation was lower, resulting in better impact resistance of this coating. The comparison of the simulation results with the impact experimental results verified that the impact damage of the coating could be effectively predicted by finite element simulation. [ABSTRACT FROM AUTHOR]

The evolution toward electric vehicle nowadays appears to be the main stream in the automotive and transportation industry. In this paper, our attention is focused on the architectural modifications that should be introduced into the car body to give a proper location to the battery pack. The required battery pack is a big, heavy, and expensive component to be located, managed, climatized, maintained, and protected. This paper develops some engineering analyses and shows sketches of some possible solutions that could be adopted. The possible consequences on the position of the vehicle center of gravity, which in turn could affect the vehicle drivability, lead to locate the battery housing below the passenger compartment floor. This solution is also one of the most interesting from the point of view of the battery pack protection in case of a lateral impact and for easy serviceability and maintenance. The integration of the battery pack’s housing structure and the vehicle floor leads to a sort of sandwich structure that could have beneficial effects on the body’s stiffness (both torsional and bending). This paper also proposes some considerations that are related to the impact protection of the battery pack, with particular reference to the side impacts against a fixed obstacle, such as a pole, which are demonstrated to be the most critical. By means of some FE simulation results, the relevance of the interplay among the different parts of the vehicle side structure and battery case structure is pointed out.

Directed energy deposition-laser beam/powder (DED-LB/Powder) is an additive manufacturing process that is gaining popularity in the manufacturing industry due to its numerous advantages, particularly in repairing operations. However, its application is often limited to case studies due to some critical issues that need to be addressed, such as the degree of internal porosity. This paper investigates the effect of the most relevant process parameters of the DED-LB/Powder process on the level and distribution of porosity. Results indicate that, among the process parameters examined, porosity is less affected by travel speed and more influenced by powder mass flow rate and laser power. Additionally, a three-dimensional finite element transient model was introduced, which was able to predict the development and location of lack-of-fusion pores along the building direction.

In this work, alumina ceramic was bonded to itself with composite foils (Ti/Cu/Ni/Cu/Ti). The thermodynamics analysis indicates that Ti-Cu liquid firstly formed and reacted with alumina to produce Ti 3 Cu 3 O reaction layer. Meanwhile, the consumption of element Ti within the Ti-Cu liquid by Ni interlayer optimized the microstructure of the joint. By thickening Ni interlayer from 0 µm to 100 µm at 1020 ℃, the joints' strength could be significantly improved by 130.6%. While the joints' strength decreased with the decomposition of reaction layer at the brazing temperature higher than 1020 ℃. The FE simulations show that the high-level stress concentration within the reaction layer could be ameliorated by Ni interlayer effectively, which was in accordance with the corresponding fracture characteristics. Although the joint's strength could be improved to 203.9 MPa by using 300 µm Ni interlayer, its improvement rate was limited with Ni interlayer constantly thickening. [ABSTRACT FROM AUTHOR]

Thermal fatigue experiments were performed on a single-edge wedge specimen of Ni-resist D5S cast iron to reproduce the conditions to which exhaust manifolds are subjected during service. The leading edge temperature was cycled between 20°C and 850°C, and the temperature distribution on the specimen surface was measured with thermocouples during thermal cycling. Due to the complexity of the loads, a uncoupled thermomechanical computation of the problem was performed using the three-dimensional finite element code ABAQUS to evaluate the temperature, stress and strain distribution over a thermal fatigue specimen. The heat fluxes and forced convection coefficients generated by the thermal fatigue benchmark were optimized in both heating and cooling phases by reverse engineering to reproduce the experimental temperature-time profiles measured by thermocouples on the surface of the specimen. Then, an elastic-viscoplastic tow-layer model was used to simulate the mechanical behavior of the studied material. It was found that the maximum stress value was located in the center of the specimen at the edge of the wedge. This result was confirmed by experimental observations. The crack initiation zone is located in the edge zone and the direction of crack propagation is perpendicular to the edge line toward the thick part of the specimen. The saturation of the main crack propagation near the uniform specimen zone was mainly explained by the rapid decrease of the energy dissipated per cycle. [ABSTRACT FROM AUTHOR]

Background: Shear damage of beams is typically brittle damage that is significantly more detrimental than flexural damage. Purpose: Based on the super-high toughness and good crack control ability of engineered cementitious composites (ECC), the shear performance of concrete–ECC beams was investigated by replacing a portion of the concrete in the tensile zone of reinforced concrete beams with ECC and employing high-strength reinforcing bars to design concrete–ECC beams. The purpose of this investigation is to elucidate and clarify the shear performance of concrete–ECC beams. Methodology/approach: Experimental and FE analyses were conducted on the shear performance of 36 webless reinforced concrete–ECC composite beams with varied concrete strengths, shear-to-span ratios, ECC thicknesses, and interfacial treatments between the layers. Results: The results indicate that the effect of the shear-to-span ratio is greater, the effect of the form of interface treatment is smaller, the effect is weakened after the ECC thickness is greater than 70 mm (i.e., the ratio of the replacement height to section height is approximately 0.35), the shear resistance is reduced when the hoop rate is greater, and the best shear resistance is obtained when the ECC 70 mm thickness and the hoop rate of 0.29% are used together. Conclusions: This study can serve as a technical reference for enhancing the problems of low durability and inadequate fracture control performance of RC beams in shear and as a guide for structural design research. [ABSTRACT FROM AUTHOR]

Epoxy‐based adhesive mortars are applied as bonding materials for the heavy‐duty fastener in buildings and constructions worldwide. The long‐term behavior of the adhesive mortars is a significant influencing factor on the sustained load and lifetime of bonded anchors. An adhesive mortar is a heterogeneous material consisting of resin and fillers. For the analysis of the long‐term performance of the bonded anchor, it is fundamental to understand the long‐term behavior of the bonding material on the microscale. This contribution presents a novel prediction approach for the long‐term load capacity of the epoxy‐based bonded anchor by using nanoindentation and FE‐simulation. The long‐term mechanical properties of the adhesive mortar were measured by using the precise nanoindentation technology on the micro level for the investigation of: (a) the loading rate effect on the load behavior of the resin, (b) the heterogeneous mechanical phases of the mortar, (c) the aging of the microstructures, and (d) the long‐term load behavior of the components of the mortar. Based on the experimental nanoindentation results, the numerical long‐term time‐independent material parameters were characterized in a concrete model by means of stochastic simulation. For analysis of the imperfection effect of a real bonded anchor, the nanoindentation was employed on the micro level to investigate the error load transfer on the interface between mortar and concrete drillhole without drill‐hole cleaning. On the macro level, the macroscale defects of an installed bonded anchor were found by using the computer tomography. It is demonstrated that the FE‐model based on the nanoindentation results can correctly predict the long‐term performances of a bonded anchorage system. [ABSTRACT FROM AUTHOR]

Pure titanium composed of α single-phase has important applications for its excellent mechanical, physical, and chemical properties, which also impose high requirements on its surface finish. However, pure titanium is a difficult-to-machine material due to its low mass transportation caused by the low stiffness and the low thermal conductivity. Thus, it is greatly needed to investigate the machinability of pure titanium by precision grinding. In the present work, we carry out experimental and finite element simulation studies on the precision multi-grain grinding of pure titanium. Specifically, finite element model of pure titanium grinding using grinding wheel with multiple grains is established, which enables the prediction of successive material removal behavior by neighboring grains in line with experiments. The machining behavior of pure titanium and its correlation with machined surface morphology and grinding force are studied by experiment, and are further revealed by finite element simulation. Subsequent grinding experiments are performed to study the effects of workpiece speed and grinding depth on the ground surface quality of pure titanium, with which a surface roughness of 0.27 μm is obtained under the optimized grinding parameters. [ABSTRACT FROM AUTHOR]

Superior ballistic performance and the lightweight character of Ti alloys are considered as main reasons for their use in armour applications against a broad spectrum of ballistic threats, e.g. bullet, fragment or blast impact. Because dynamic loading caused by typical penetrators is characterized by high strain rates, only specific test methods allow a closer investigation of the respective material behaviour. In the present study, quasi-static and dynamic compression tests as well as ballistic tests were conducted on a twophase α+β alloy Ti-6Al-4V (in m%) manufactured by hot-rolling. Post-deformation heat treatments, influencing microstructure and mechanical properties were applied in order to compare three different microstructural configurations: as-rolled, mill-annealed and bimodal. While, on the one hand, ballistic tests were employed for the determination of the ballistic limit velocity v50, compression tests, on the other hand, delivered essential input parameters for the application of the Johnson-Cook constitutive model in a finite element simulation of the impact event. The comparison of experimental results to simulation results was supplemented by means of microstructural characterization of tested samples with the focus set on the prevalently observed deformation and damage mechanisms, as for example adiabatic shearing. [ABSTRACT FROM AUTHOR]