Finite Element Analysis Program Research Articles

Analysis of stress distribution in implant-supported prostheses with custom abutments at different angles of 20 degrees: A finite element analysis

Aim: Implants may not always be placed parallel to each other. In such cases, implants can be made more parallel by adjusting the angles with custom abutments. Different cementation materials can be used for cement-retained abutments. The bonding and stress resistance values of materials used in the cementation of implant-supported prostheses vary. The aim of this study is to demonstrate the stress distribution values of restorations bonded with different cementation materials in finite element analysis. Methodology: In this study, a maxillary edentulous jawbone was designed using the SolidWorks program. Two implants were placed in the regions of teeth #14 and #16. Implant data was obtained from the Bilimplant company. A 20-degree angled custom abutment and implant-supported prosthesis were designed using the Exocad program. Standard Tesellation Language (STL) files were transferred to SolidWorks to obtain Standard for the Exchange of Product Model Data (STP) files. The created prosthesis design was then transferred to the ABAQUS program for finite element analysis. Subsequently, using 5 different cementation materials (glass ionomer cement, dual-cure resin cement - ivoclar, dual-cure resin cement - relyx, polycarboxylate cement, self-cure resin cement), stress distribution values of implant-supported prosthesis components were recorded as von Mises stress values (VMS) Results: İndicate higher stress values with glass ionomer cement and lower with polycarboxylate cement. Stress distribution increases posteriorly but doesn't significantly differ based on cement type. Lowest stress on implant screws is with glass ionomer, but highest varies. Cortical bone stress is lowest with glass ionomer cement. Conclusion: There was no significant difference in stress values among different cement types. Stress increases in implants, abutments, and cements due to forces applied posteriorly, while anteriorly, retention screw stress increases. The choice of cementation material does not significantly impact stress in implant components or surrounding tissues.

Analytical study on fire resistance performance of precast concrete hollow-core slabs for electric vehicle fire in parking structures

This study evaluated the effects of fires that occur in internal combustion engine vehicles (ICEVs) and battery electric vehicles (BEVs) on the structural safety of hollow-core slabs (HCS) installed in parking structures. A fire simulation of a prototype parking structure was performed using the time–heat release rate curves of ICEVs and BEVs derived from fire experiments, and fire behavior and temperature history were derived according to the fire curve. Additionally, nonlinear finite element analysis was conducted using a general-purpose finite element analysis program, and the fire resistance performance of HCS was evaluated according to the fire curve and slab load ratio. In the case of a fire in ICEVs, the performance criteria of ISO 834–1 were met even at a slab load ratio of 0.7. However, in the case of a fire in BEVs, the standard for insulation was not met as the temperature change of the upper surface of HCS exceeded 180 K, and the load-bearing capacity was also not satisfied as the limiting deflection reached a slab load ratio of 0.7.

Active Vibration Control Performance Comparison Based on Middle Pedestal Stiffness Using a Mobility Model and the Narrowband Fx-LMS Technique

Vibrations generated from equipment mounted on ships radiate into the water and affect covert operation capabilities. Accordingly, various studies are being conducted to reduce vibration transmitted from mounted equipment. In this study, a system consisting of mounting equipment, a 3-axis active mount, a middle pedestal, and a lower mount of the middle pedestal was modeled using a finite element analysis program, and a mobility model was constructed by calculating the frequency response function between the positions required for analysis. The error signal (primary path) obtained using the mobility model and the response at the operating point by the control force of the actuator (secondary path) are applied to the narrowband Fx-LMS algorithm for vibration control, and the control performance was compared. Through coupling analysis of the middle pedestal, the control influence according to the rigidity of the middle pedestal was analyzed. As a result of the control simulation, the time required for vibration control was controlled approximately 6 times faster in the model, with increased stiffness of the middle pedestal, and the vibration reduction performance was predicted to improve by a minimum of 0.9 dB and a maximum of 13.3 dB. Through this study, a simulation model that can provide a guide for the design of the middle pedestal of a ship was obtained, and it is expected that it can be utilized for a preliminary design review before manufacturing the middle pedestal of a ship.

A Study on the Bearing Performance of an RC Axial Compression Shear Wall Strengthened by a Replacement Method Using Local Reinforcement with an Unsupported Roof

When compared with conventional replacement reinforcement methods, the method of replacement using a local reinforcement with an unsupported roof has the advantages of shortening the reinforcement cycle and reducing material loss, and many scholars have carried out useful explorations thereof. At present, the formula for the bearing capacity of reinforcement by replacing concrete in the Code does not consider the effect of stress hysteresis on the parts of the reinforcement; so when the initial stress level is greater than 0.4, the Code’s strength utilization coefficient of 0.8 for the new concrete in the replaced area is on the side of insecurity. In this study, we are trying to improve and supplement the formula in the Code through the following work. Firstly, 18 groups of shear wall models were constructed using a VFEAP finite element analysis program to analyze the bearing performances of the shear walls after the replacement. The results showed that the replacement concrete strength, the initial stress level and the size of the replaced area had a significant influence on the bearing capacity of the shear wall after the replacement. Secondly, utilizing the replacement concrete strength, the initial stress level and the size of the replacement area as key parameters, then introducing the strength improvement coefficient considering the constraints of the stirrups, the modified strength utilization coefficient of new concrete in the replaced area was formulated. Finally, based on the modified strength utilization coefficient, the replacement bearing capacity formulas for the one-batch, two-batch, and three-batch replacements were derived, and an N-batch replacement bearing capacity formula was regressed and fitted on the basis of these equations, which are less discrete and more secure than the Code’s formula.

Computer Modelling Study of Volume Kinetics in Intraocular Segments Following Airbag Impact Using Finite Element Analysis.

We have previously studied the physiological and mechanical responses of the eye to blunt trauma in various situations using finite element analysis (FEA). In this study, we evaluated the volume kinetics of an airbag impact on the eye using FEA to sequentially determine the volume change rates of intraocular segments at various airbag deployment velocities. The human eye model we created was used in simulations with the FEA program PAM-GENERISTM (Nihon ESI, Tokyo, Japan). Different airbag deployment velocities, 30, 40, 50, 60 and 70 m/s, were applied in the forward direction. The volume of the deformed eye impacted by the airbag was calculated as the integrated value of all meshes in each segment, and the decrease rate was calculated as the ratio of the decreased volume of each segment at particular timepoints to the value before the airbag impact. The minimum volume of the anterior chamber was 63%, 69% and 50% at 50, 60 and 70 m/s airbag impact velocity, respectively, showing a curve with a sharp decline followed by gradual recovery. In contrast to the anterior chamber, the volume of the lens recovered promptly, reaching 80-90% at the end of observation, except for the case of 60 m/s. Following the decrease, the volume increased to more than that of baseline at 60 m/s. The rate of volume change of the vitreous was distributed in a narrow range, 99.2-100.4%. In this study, we found a large, prolonged decrease of volume in the anterior chamber, a similar large decrease followed by prompt recovery of volume in the lens, and a time-lag in the volume decrease between these tissues. These novel findings may provide an important insight into the pathophysiological mechanism of airbag ocular injuries through this further evaluation, employing a refined FEA model representing cuboidal deformation, to develop a more safe airbag system.

Numerical Analysis of Blast Behavior for Non-ideal Explosive ANFO in Shock-Tube Test

In an explosion test using a shock tube, the behavior of pressure waves can be reproduced with high reliability. However, the explosion in a shock tube occurs in a confined space. It is difficult to predict the behavior of pressure waves and its effect on various concrete specimens by using the research findings related to free-field explosions. Moreover, few studies have focused on explosive-driven shock tubes. In this study, the behavior of pressure waves in a shock tube was numerically analyzed using a finite-element analysis program. The explosive used to generate the pressure waves was an ammonium nitrate fuel oil (ANFO), which exhibits non-ideal explosion characteristics. The Jones–Wilkins–Lee (JWL) and ignition-and-growth (I&G) equations of state were used for blast-pressure calculation. The analysis results were affected by factors such as the release rate of explosive energy and the development of the pressure waves in the confined explosion. The blast behaviors, such as the low release rate of explosive energy and the resulting increase in the impulse, were analyzed using the ignition-and-growth equation. The impulse produced during the development of waves reflected by the block installed at the tube inlet exceeded that produced by the tube wall. Such behaviors that occurred at the beginning of a blast affected the process of wave propagation along the shock tube and the wave reflection due to the test specimen at the outlet of the shock tube. In this study, the blast behavior in the shock tube, which could be referenced for the analysis of blast overpressure and its effect on concrete specimens, was numerically analyzed. Further research on the structural behaviors of concrete specimens due to blast overpressure is needed.

Estimation of residual stress in dissimilar metals welding using deep fuzzy neural networks with rule-dropout

Welding processes are used to connect several components in nuclear power plants. These welding processes can induce residual stress in welding joints, which has been identified as a significant factor in primary water stress corrosion cracking. Consequently, the assessment of welding residual stress plays a crucial role in determining the structural integrity of welded joints. In this study, a deep fuzzy neural networks (DFNN) with a rule-dropout method, which is an artificial intelligence (AI) method, was used to predict the residual stress of dissimilar metal welding. ABAQUS, a finite element analysis program, was used as the data collection tool to develop the AI model, and 6300 data instances were collected under 150 analysis conditions. A rule-dropout method and genetic algorithm were used to optimize the estimation performance of the DFNN model. DFNN with the rule-dropout model was compared to a deep neural network method, known as a general deep learning method, to evaluate the estimation performance of DFNN. In addition, a fuzzy neural network method and a cascaded support vector regression method conducted in previous studies were compared. Consequently, the estimation performance of the DFNN with the rule-dropout model was better than those of the comparison methods. The welding residual stress estimation results of this study are expected to contribute to the evaluation of the structural integrity of welded joints.

Simulation of Changes in Tensile Strain by Airbag Impact on Eyes After Trabeculectomy by Using Finite Element Analysis.

We studied the kinetic phenomenon of an airbag impact on eyes after trabeculectomy using finite element analysis (FEA), a computerized method for predicting how an object reacts to real-world physical effects and showing whether an object will break, to sequentially determine the responses at various airbag deployment velocities. A human eye model was used in the simulations using the FEA program PAM-GENERISTM (Nihon ESI, Tokyo, Japan). A half-thickness incised scleral flap was created on the limbus and the strength of its adhesion to the outer sclera was set at 30%, 50%, and 100%. The airbag was set to hit the surface of the post-trabeculectomy eye at various velocities in two directions: perpendicular to the corneal center or perpendicular to the scleral flap (30° gaze-down position), at initial velocities of 20, 30, 40, 50, and 60 m/s. When the airbag impacted at 20 m/s or 30 m/s, the strain on the cornea and sclera did not reach the mechanical threshold and globe rupture was not observed. Scleral flap lacerations were observed at 40 m/s or more in any eye position, and scleral rupture extending posteriorly from the scleral flap edge and rupture of the scleral flap resulting from extension of the corneal laceration through limbal damage were observed. Even in the case of 100% scleral flap adhesion strength, scleral flap rupture occurred at 50 m/s impact velocity in the 30° gaze-down position, whereas in eyes with 30% or 50% scleral flap adhesion strength, scleral rupture was observed at an impact velocity of 40 m/s or more in both eye positions. An airbag impact of ≥40 m/s might induce scleral flap rupture, indicating that current airbags may induce globe rupture in the eyes after trabeculectomy. The considerable damage caused by an airbag on the eyes of short-stature patients with glaucoma who have undergone trabeculectomy might indicate the necessity of ocular protection to avoid permanent eye damage.

Finite Elements Analysis and Topology Optimization of Parking Brake Lever and Ratchet

Topology optimization is known as one of the basic categories of structural optimization. Topology optimization is received increasing attention in many engineering disciplines. Topology optimization contributes to minimizing emissions and environmental effects by increasing material utilization efficiency and manufacturing sustainability. The mechanical parking brake is still used in many vehicles. This study aims to contribute to the reduction in vehicle weight by applying topology optimization. In addition, it also purposes to promote sustainability in manufacturing by reducing material usage and energy consumption. A CAD model was created by considering the existing mechanism element dimensions. The parking brake lever mechanism component was evaluated using topology optimization and finite element analysis methods. Static analyses were performed using a finite element analysis program. The results of this analysis were used as input data for topology optimization. In the topology optimization, the response constraint mass was increased by 5 increments from 50% to 95%. As a result, the maximum equivalent (von Mises) stress for the parking brake lever is 230,29 MPa, and for the ratchet is 11,559 MPa. The maximum total deformation value for the brake lever is 0,95853 mm and for the ratchet is 0,0079482 mm. The parking brake lever mass decreased by 18,48% from 0.27751 kg to 0.22622 kg. The ratchet mass decreased from 0.095042 kg to 0.061911 kg by 34.85%.

Numerical simulation of the 2010 4-story reinforced concrete structure tested on the E-defense shake table

Due to advancements in computational tools, performing a full nonlinear response history analysis of structures at the system level using detailed numerical simulations of components has become less demanding, even on standard personal computers. However, the modelling approaches need to be calibrated and verified against experimental measurements to ensure the accuracy of the system-level predictions. In this study, an advanced numerical simulation method is used to predict the 3D nonlinear dynamic response of a four-story reinforced concrete building tested at E-Defense shake table. The structure is modelled in the finite element analysis programme DIANA, using a previously developed and validated approach to predict the failure modes of doubly reinforced walls with confined boundary regions. Curved shell elements are used to model the walls and slabs, and the reinforcement is modelled using embedded bar elements. The frame elements are modelled using beam elements with the effect of confinement on the concrete behaviour represented in the material constitutive model. The numerical versus experimental response comparison is conducted at both local and global levels. For local levels, the base shear versus top displacement curves, strain gradients as well as the crack pattern predicted by the numerical model are compared with the test measurements. The inter-story drift response history is considered as the metric for the global level assessment. The effects of different modelling parameters on the accuracy of predictions are also investigated.

EXPERIMENTAL AND ANALYTICAL INVESTIGATION OF THE EFFECT OF LAYER NUMBER AND THICKNESS ON THE BENDING PROPERTIES OF GLULAM BEAMS

Wooden material is used in structural elements due to its many positive properties. Recent years have witnessed a surge in research directed toward enhancing the mechanical properties of wooden beams through the utilization of materials like steel plates and fiber reinforced polymers (FRP). Layered laminated timber, a composite material crafted from wood, serves as a testament to this endeavor. These laminated timbers constitute intricate engineering elements, fashioned from layers of wood characterized by distinct levels of strength and hardness, systematically arranged as per established guidelines. The present study is geared toward a comprehensive examination of the bending characteristics exhibited by glued beams, fashioned from spruce trees, encompassing six distinct sizes and varying layer counts. The manufacturing process yields beams with diverse cross-sectional profiles, including 3-layer and 7-layer variants. By performing 4-point bending tests of the beams, maximum load carrying capacity, bending strength, and elasticity modulus values were obtained experimentally. In addition to the experimental analyses, numerical models of the produced beams were created using the finite element analysis program, and static analyses were performed. In the experimental results, it was observed that the bending properties of the beams increased as the number and size of layers increased. It was determined that the maximum load carrying capacity, bending strength, and elasticity modulus values obtained as a result of experimental and numerical analysis were very close to each other. Numerical analysis results showed that beams produced with various number of layers and thicknesses can be simulated. It has been determined that the results obtained by creating numerical models instead of experimental analyses for this type of wooden beam may be sufficient.

Design and manufacturing process of pneumatic soft gripper for additive manufacturing

The soft gripper, constructed from elastic materials, serves as a crucial automated device component, aiming to minimize object damage. The central focus of utilizing soft grippers lies in their shape design, enabling effective handling of objects with low rigidity and diverse forms. This study delves into shape design research, employing a pneumatic pressure-responsive, tube-like soft gripper fabricated through injection molding. During the design phase, a comprehensive survey of soft gripper research trends was conducted, leading to two distinct configurations: Type1, drawing from established shapes, and Type2, a novel design ensuring bending angle stability. The primary dimensions of Soft Gripper Type 1 and Type 2 are as follows: lengths of 78.11 mm and 74.96 mm, heights of 18.69 mm and 20.0 mm, respectively, with a uniform thickness of 0.6 mm. The prediction of bending angles was accomplished through employment of the Abaqus finite element analysis program. In both simulation and experimentation, pneumatic pressures of 100, 200, and 300 kPa were applied to compare the bending angles of two types of soft grippers. While conventional injection molding remains a prevalent manufacturing technique, it confronts challenges like demolding and undercuts. Thus, for intricate shapes and monolithic soft grippers, layer-by-layer additive manufacturing emerges as a superior choice over injection molding. The implementation of this approach holds the potential for streamlined soft gripper design processes, potentially yielding reductions in both time and cost. The significance of these findings lies in advancing the capabilities of soft grippers, propelling them toward efficient and cost-effective applications in various fields.

The reduction of noise and vibration of composite panels in aircraft through multi-dimensional particle swarm optimization

The reduction of noise and vibrations on aircraft poses a unique challenge. This paper explores the use of multi-dimensional Particle Swarm Optimization (PSO) to reduce vibrations and transmitted noise in composite fuselage panels excited by turbulent boundary layer flow. Turbulent boundary layer Power Spectral Density (PSD) data is used to simulate the excitation of simply supported aircraft panels. A comparison is made between isotropic aluminum 2024-T3 panels and optimized composite panels of varying composition for the assessment of success in noise transmission reduction as well as structural function. The algorithm for PSO is implemented in Python and iterates through composites with varying thickness, ply makeup, ply orientation, and materials. Python allows for complex algorithms to be easily interfaced with Finite Element Analysis (FEA) programs. In the current study, ANSYS is used to determine the spectral response of the panels subject to turbulent flow using the superposition of the modes of vibration. During the optimization process, optimization parameters are updated in each iteration based on the success of reducing the spectral response of the panel without compromising its structural integrity or increasing its weight beyond a reasonable threshold.

Finite Element Analysis of Changes in Deformation of Intraocular Segments by Airbag Impact in Eyes of Various Axial Lengths.

We studied the kinetic phenomenon of an airbag impact on eyes with different axial lengths using finite element analysis (FEA) to sequentially determine the physical and mechanical responses of intraocular segments at various airbag deployment velocities. The human eye model we created was used in simulations with the FEA program PAM-GENERISTM. The airbag was set to impact eyes with axial lengths of 21.85 mm (hyperopia), 23.85 mm (emmetropia) and 25.85 mm (myopia), at initial velocities of 20, 30, 40, 50 and 60 m/s. The deformation rate was calculated as the ratio of the length of three segments, anterior chamber, lens and vitreous, to that at the baseline from 0.2 ms to 2.0 ms after the airbag impact. Deformation rate of the anterior chamber was greater than that of other segments, especially in the early phase, 0.2-0.4 ms after the impact (P < 0.001), and it reached its peak, 80%, at 0.8 ms. A higher deformation rate in the anterior chamber was found in hyperopia compared with other axial length eyes in the first half period, 0.2-0.8 ms, followed by the rate in emmetropia (P < 0.001). The lens deformation rate was low, its peak ranging from 40% to 75%, and exceeded that of the anterior chamber at 1.4 ms and 1.6 ms after the impact (P < 0.01). The vitreous deformation rate was lower throughout the simulation period than that of the other segments and ranged from a negative value (elongation) in the later phase. Airbag impact on the eyeball causes evident deformation, especially in the anterior chamber. The results obtained in this study, such as the time lag of the peak deformation between the anterior chamber and lens, suggest a clue to the pathophysiological mechanism of airbag ocular injury.

Three-dimensional creep calculation model for reliability analysis of concrete-filled steel tubular (CFST) structure

For long-span concrete-filled steel tube (CFST) structure, it is essential to implement efficient and realistic prediction models for the long-term processes of core concrete creep. In order to systematically study the main influential factors in CFST structure creep effects, a probabilistic analysis can be performed. The objective of this paper is to analyse the long-term response of CFST structure by using time-dependent reliability method. To address the problem of creep calculation, a novel and comprehensive presentation was developed. By converting the integral-type creep law to a differential-type form with internal variables, based on the Kelvin chain model, an elastic structural analysis with generally orthotropic elastic moduli and eigenstrains was established. We have compiled a three-dimensional (3-D) finite-element analysis programme that considers the creep Poisson effect of core concrete to analyse the long-term performance of the CFST structure. This is achieved by developing a commercial finite element code, such as Usermat in ANSYS. As calculation examples, several time-dependent analyses of a CFST stub column and long-span CFST arch bridge were performed. The calculated results of long-term behaviour agree well with experimental and measured data. Considering the randomness of various input parameters, such as physical dimensions and materials of the CFST structure, we have analysed the uncertainty using the Latin-hypercube-sampling (LHS) stochastic finite-element method. The results of creep sensitivity analysis revealed that coefficient of creep model uncertainty, steel and concrete elastic modulus were the three most influential parameters for CFST stub columns’ creep, and load, coefficient of creep model uncertainty, relative humidity, steel and concrete elastic modulus were the five for CFST arch bridges’ long-term deflection. In addition, the use of Monte Carlo (MC) and response surface (RS) methods for structural stochastic reliability analysis demonstrates the ability of these approaches to assess the reliability index of long-span CFST arch bridges. This provides a valuable reference for the design and performance evaluation of CFST structures.

Enhancing thermal efficiency of aluminum heat sink by reduced graphene oxide-layer coating approach

Light emitting diode (LED) technology plays a significant role in the market of lighting technologies due to its high efficiency compared to conventional lighting solutions. Cooling of high-power LEDs, on the other hand, is a critical aspect in maximizing LED performance. Furthermore, due to the powder, rain, and muds, LED armatures including a finned heat sink may not be efficient according to its design and utilization areas especially for outdoor illumination. Eliminating these factors, un-finned heat sink LED armatures are also preferred, yet the temperature dissipation of the un-finned type is not homogeneous relatively according to finned type. In this study, a graphene coated un-finned heat sink was developed to obtain relatively homogeneous temperature distribution and increase heat transfer of aluminum plate. An un-finned heat sink comprising thin graphene film was designed by a computer-aided-design (CAD) program and the thermal analysis was conducted by a finite element analysis (FEA) program. The experimental measurements offered that the maximum and minimum junction temperatures for the bare, and reduced graphene oxide (rGO)-layers coated aluminum heat sinks were obtained as 90 − 70◦C, and 59–54◦C, respectively. The outstanding in-plane thermal conductivity of rGO-layers facilitated the homogenous heat distribution throughout the aluminum heat sink. Moreover, the design and thermal analysis of developed heat sinks were validated with experimental results with the 2.4% error with respect to maximum junction temperature. It can be concluded that rGO-layers coated aluminum heat sink enabled to facilitated the heat transfer more than bare aluminum due to its higher thermal conductivity. In brief, this work opens a new gate for designing the graphene based materials-integrated cooling solution for LED applications.

The Effect Of Pre-Forming On The Forged Part In the Hot Forging Process

Analysis programs based on finite elements have great importance in verifying the design and production processes. In the automotive industry, many parts are produced by hot forging process. The die designs of the parts to be produced by hot forging process are verified by finite element analysis programs. In this study, the importance of pre-forming in hot forging process is investigated by using finite element method and the necessity of pre-forming is indicated by the analysis. In the analysis phase of the study, hot forging finite element analysis was performed for 4 different cases of the torque rod housing that one of the suspension parts of heavy commercial vehicles part using FORGE NxT program. In addition, experimental studies were carried out for these cases and the results obtained were compared with the analysis results. The results obtained as a result of the analysis and experimental study were found to be consistent with each other. It has been observed that pre-forming is very important and necessary in the hot forging process in order to increase die life and to reduce die runaway, crease and non-filling problems.

INVESTIGATION OF THE AUXETIC BEHAVIOR OF AN ORIGINAL LATTICE STRUCTURE DESIGN

Auxetic structures are special structures with negative Poisson's ratio due to their geometric shapes in their internal structure. When tensile force is applied to these structures, transverse and longitudinal expansions are observed, while transverse and longitudinal contractions are observed when compressive force is applied. There are many different unit cell designs such as chiral, arrowhead, re-entrant in auxetic structures. In this study, a unique cell design was studied and the behavior of an auxetic lattice structure was investigated. The lattice structure designed with different geometric thicknesses and different matrices was analyzed with the finite element analysis program and found to have a negative Poisson's ratio. In the designed lattice structure, the structure with 4×4 matrix and 3 mm geometric thickness was found to have the best negative Poisson's ratio.

A modal-based method for blast-induced damage assessment of reinforced concrete columns: Numerical and experimental validation

Reinforced concrete (RC) columns play a crucial role in the overall performance of modern RC frame buildings under blast loading. The RC columns under blast loads might experience various irreversible consequences such as concrete cracks, crushing and spalling, changing the status of both modal properties and load-carrying capacity. In this paper, the blast-induced damage assessment of the RC columns involving the measurement of modal parameters was introduced and validated. Firstly, a modal-based method for blast-induced damage assessment of RC columns was proposed, in which the damage is characterized as the reduction of axial bearing capacity and further expressed as the explicit function of the vibration frequencies and the mass-normalized displacement mode shapes. Then, the finite-element analysis program LS-DYNA was employed to establish the numerical model of RC columns under axial compression loads and lateral blast loads. The residual load-bearing capacities and modal properties of the RC columns were illustrated. By using the numerical results collected in the present study, the validity of the proposed damage assessment method was discussed and proved numerically. Further, field explosion tests and experimental modal tests were conducted, and the results showed that the modal-based damage assessment method exhibited remarkable agreement with the blast damage determined by residual bearing capacities. Based on the numerical and experimental results, the proposed modal-based damage assessment method is applicable for the non-destructive evaluation of blast-induced damage of RC columns.

Themomechanical Response of an Additively Manufactured Hybrid Alloy by Means of Powder Bed Fusion

The laser powder bed fusion (L-PBF) technique was utilized to manufacture a hybrid M789-N709 alloy by depositing M789 steel on wrought N709 steel. The tensile strength of the M789-N709 interface generated during the process has been established to be higher than that of the base materials. In the previous work of the current authors, extensive characterization of the M789-N709 interface (before and after heat treatment) was performed by means of electron backscatter diffraction, electron probe microanalysis, transmission electron microscopy with energy dispersive spectroscopy, and atom probe tomography analyses, to understand the mechanisms associated with its superior strength. In the present work, since the application of the hybrid alloy is targeted towards an elevated temperature environment, the individual high-temperature mechanical properties of M789 and N709 steels were acquired at various temperatures and strain rates using a Gleeble 563 thermomechanical system. Then, based on the flow curves, phenomenological-, and physical-based constitutive material models were established. These constitutive models can be utilized to accurately assess the high-temperature response of the hybrid alloy system using finite element analysis programs. This work demonstrates the application of thermomechanical processing and constitutive modeling in the field of metal additive manufacturing.