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This study investigates the effect of laser volume energy density (VED) on the properties of AISI 420 stainless steel and TiN/AISI 420 composite manufactured by selective laser melting (SLM). The composite contained 1 wt.% TiN and the average diameters of AISI 420 and TiN powders were 45 µm and 1 µm, respectively. The powder for SLMing the TiN/AISI 420 composite was prepared using a novel two-stage mixing scheme. The morphology, mechanical, and corrosion properties of the specimens were analyzed, and their correlations with microstructures were investigated. The results showed that the surface roughness of both SLM samples decreases with increasing VED, while relative densities greater than 99% were achieved at VEDs higher than 160 J/mm3. The SLM AISI 420 specimen fabricated at a VED of 205 J/mm3 exhibited the highest density of 7.7 g/cm3, tensile strength (UTS) of 1270 MPa, and elongation of 3.86%. The SLM TiN/AISI 420 specimen at a VED of 285 J/mm3 had a density of 7.67 g/cm3, UTS of 1482 MPa, and elongation of 2.72%. The microstructure of the SLM TiN/AISI 420 composite displayed a ring-like micro-grain structure consisting of retained austenite on the grain boundary and martensite in the grain. The TiN particles strengthened the mechanical properties of the composite by accumulating along the grain boundary. The mean hardnesses of the SLM AISI 420 and TiN/AISI 420 specimens were 635 and 735 HV, respectively, which exceeded previously reported results. The SLM TiN/AISI 420 composite exhibited excellent corrosion resistance in both 3.5 wt.% NaCl and 6 wt.% FeCl3 solutions, with a resulting corrosion rate as low as 11 µm/year.

This article discusses the anti-skid braking control mechanism of an aircraft. A proportional-integral (PI) controller is used by wheels to generate the desired braking torque to stop the aircraft while landing. Potential runway variations are considered, which will affect the friction force available to each wheel. Variations in wheel forces generate drag torque, causing the aircraft to drift away from the runway. As a result, a supervisory consensus controller has been introduced, which will adjust the braking torque of each wheel to achieve equal force on each wheel. Losses due to the wireless communication channel affect the performance of the consensus controller; therefore, packet losses have been studied. The proposed model is tested and simulated to find out how well the consensus controller works over a noisy channel.

Ultrashort pulsed laser is a promising tool for processing transparent materials. We report on a new approach that simultaneously creates a pair of conjugate grooves on the bottom surface of a thin glass substrate at the duration of plowing a V-shaped microgroove on the top surface using the technique of direct laser ablation. We propose a hypothesis to explain the accompanying grooves’ formation mechanism and simulate Maxwell’s equations to verify its applicability. Measurements showed the surface roughness of the groove’s sidewalls was 0.14 $\mu \text{m}$ . This method requires no mask, can be directly performed in the atmosphere, and can simultaneously produce microgrooves on both sides of the substrate that render it an effective approach for producing high quality V-shaped microgrooves on both sides of the substrate.

Laser machining has been emerging as a powerful alternative for cutting thin metal substrates. In this study, the application of pulsed laser cutting of a thin nonoriented silicon steel, with a thickness of 0.1 mm, was studied. The four processing parameters considered were laser power, cutting speed, pulse repetition rate, and processing environment. The two outputs to be measured were the extent of heat-affected zone (HAZ) and deviation of magnetic flux density (MFD) from initial value. Each input was designed with three levels and the three processing environments were air, deionized water, and sodium chloride solution. Based on the experimental design of the L27 Taguchi method, 27 parameter sets out of the total of 81 sets were used for the experiment. Results show that HAZ and MFD were negatively correlated. Compared with processing in air, cutting in the liquid could effectively reduce the HAZ. In the 27 experimental cases, the achieved minimum HAZ was 34.5 μm that corresponded to retaining 99% of initial MFD. The importance of the input was analyzed by the random forest method. The most and second significant parameters were laser power and environmental condition and their importance levels were 50.82% and 40.99%, respectively. Four artificial intelligence (AI) prediction models, full quadratic multiple regression analysis, artificial neural network, random forest, and extreme learning machine (ELM), were established based on randomly selecting 80% of the 27 data sets for training and the remaining 20% for testing. Model verification was executed by arbitrarily taking 10 additional new predictive parameter sets, from the remaining 54 parameter sets, for experiments. After comparing the predicting and experimental results, ELM model was found to have the best forecast performance. Thus, it was chosen as the target model for output optimization by the genetic algorithm method (GA). Through implementing the predicted optimal processing parameters from the resulting ELM-GA algorithm for the confirmation experiment, the obtained MFD and HAZ were 1.639 T and 30.41 μm, respectively, which were very close to that of the predicted optimal outputs, 1.640 T for MFD and 29.90 μm for HAZ.

This paper presents an efficient method for designing optimal controllers. First, we established a performance index according to the system characteristics. In order to ensure that this performance index is applicable even when the state/output of the system is not within the allowable range, we added a penalty function. When we use a certain controller, if the state/output of the system remains within the allowable range within the preset time interval, the penalty function value is zero. Conversely, if the system state/output is not within the allowable range before the preset termination time, the experiment/simulation is terminated immediately, and the penalty function value is proportional to the time difference between the preset termination time and the time at which the experiment was terminated. Then, we used the Nelder–Mead simplex method to search for the optimal controller parameters. The proposed method has the following advantages: (1) the dynamic equation of the system need not be known, (2) the method can be used regardless of the stability of the open-loop system, (3) this method can be used in nonlinear systems, (4) this method can be used in systems with measurement noise, and (5) the method can improve design efficiency.

The aim of this study is to develop a finite element analysis technique to characterize the distributions of temperature and stress in the process of multilayer deposition of metallic powders by laser additive manufacturing (LAM). Simulation results indicate the residual normal stress in the laser moving direction is greater than that in other directions due to a larger temperature gradient, and it increases with number of deposited layers. Highly residual stresses are present in the LAM build and at the base nearby the interface between the build and base.

Water vapor transmission rate (WVTR) of a barrier film is evaluated after combined cyclic-static bending. Results show that cyclic bending combined with a static bending deteriorates the barrier performance to a greater extent, compared with pure cyclic bending. For a severe bending radius of 2.5 mm, WVTR is increased at the beginning of combined cyclic-static bending. There is a little effect of static bending on WVTR for a short hold time. However, for a longer period of static hold-time, the contribution of static bending to deterioration in the performance of barrier thin film is visible.

A testing method is developed to quantitatively determine the thermo-mechanical cycling life in oxidizing atmosphere for the joint between a solid oxide fuel cell glass-ceramic sealant and a ferritic stainless steel interconnect. Thermo-mechanical cycling tests are performed under cyclic shear or tensile loading in conjunction with cyclic temperature variance between 40 °C and 800 °C. Results reveal thermo-mechanical cycling life under both shear and tensile loadings increases with a decrease in end stress at 800 °C, for a certain end stress at 40 °C. Nevertheless, for a certain end stress at 800 °C, the tensile thermo-mechanical cycling life increases with a decrease in end stress at 40 °C, while the shear thermo-mechanical cycling life is independent of end stress at 40 °C. A difference in fracture pattern is also observed between shear and tensile loadings. For shear loading, fracture mainly takes place along the interface between glass-ceramic sealant and an oxide layer, such as BaCrO4 or Cr2O3. However, for tensile loading, fracture mainly occurs within the glass-ceramic layer, following crack initiation at the interface of Cr2O3/sealant or Cr2O3/BaCrO4.

Mechanical properties and microstructure are investigated for a martensitic stainless steel (AISI 420) fabricated by selective laser melting (SLM) in three build directions. The tensile specimens built by SLM are classified into three groups. Group A is horizontally built in the thickness direction, Group B is horizontally built in the width direction, and Group C is vertically built in the length direction. The loading direction in tensile test is parallel to the build direction of Group C, but perpendicular to that of Groups A and B. Experimental results indicate build direction has significant effects on the residual stress, hardness, and tensile properties of SLM builds. Microstructural analyses indicate the as-fabricated SLM AISI 420 builds exhibit elongated cells and acicular structures which are composed of martensite and retained austenite phases growing along the build direction. Such anisotropy in the microstructure leads to anisotropic mechanical properties as Group C specimens (length direction) exhibit greater yield stress, ultimate tensile stress, and elongation than the specimens of Groups A (thickness direction) and B (width direction). The residual compressive stress in the gauge section also contributes to the superior tensile properties of Group C (length direction), as compared to Groups A (thickness direction) and B (width direction), which exhibit residual tensile stress in the gauge section.

The representation of non-spherical particles in discrete element method (DEM) has not been addressed adequately. Although the multiple sphere method (MSM) is the most popular approach to describe non-spherical particle shape, the validity of the MSM has not been established yet. The purpose of this study is to examine the validity and adequacy of the MSM. A uni-axial confined compression test was designed and set up to study the mechanical behaviour of an ellipsoidal granular assembly under vertical loading and the load transfer to the contacting boundary. Four levels of multi-sphere approximation for an axi-symmetric ellipsoidal particle were employed in DEM simulation to investigate the adequacy of multi-sphere approximation. A comparison on compression characteristics between the numerical and experimental results was made and discussed in this paper. Most of the compared physical properties showed reasonable agreement, indicating that capturing the key linear dimensions of a non-spherical particle may be sufficient to predict reasonable results. A small number of sub-spheres (say, N ≥ 5) for representing an axi-symmetric ellipsoidal particle can give plausible results. However, the DEM simulations also produced a certain extent of discrepancy in loading stiffness with experiments. Plausible explanations are provided and require further investigation.

Creep rupture is investigated at 800 °C of a joint between a glass-ceramic sealant and a ferritic stainless steel interconnect coated with lanthanum strontium manganite for solid oxide fuel cell application. Results reveal the shear and tensile creep strength of the as-joined, non-aged joint at a rupture time of 1000 h is about 42% and 3% of the average shear and tensile bonding strength, respectively. A thermal aging of 1000 h at 800 °C enhances the creep strength. For both non-aged shear and tensile specimens with a short creep rupture time, fracture mainly takes place in an oxyapatite interlayer which is formed in the joining process. For a medium creep rupture time, fracture site changes to a mixed BaCrO4/oxyapatite layer. Oxyapatite and BaCrO4 dominate the creep failure mechanism for 1000 h-aged shear specimens, while (Cr,Mn)3O4 spinel plays a role in the creep failure of 1000 h-aged tensile specimens.

Effects of cyclic bending on the encapsulation properties of a barrier thin film are investigated. Water vapor transmission rate (WVTR) of the given barrier film is measured after variously cyclic bending conditions using a calcium corrosion test technique. Experimental results show that microcracks in the barrier thin film are found after applying a certain number of bending cycles. They are responsible for an increase in WVTR. Given a bending radius, a greater number of bending cycles leads to a larger amount of damage, and consequently a greater extent of moisture ingress. A smaller bending radius produces a greater amount of damage than a larger one, in a short period of loading time (≤104 cycles). However, after 105 cycles of cyclic bending, the amount of damage reaches a saturated level regardless of bending radius, as all the WVTR values become comparable. A simplified 3D finite element analysis (FEA) model is established in microscale to analyze the moisture diffusion mechanism. Numerical results show that, with the presence of cracking and delamination, the WVTR value increases significantly. Good agreement between the simulation and experimental measurements on WVTR confirms that the failure mechanism involves cracking and delamination under cyclic bending. The 3D FEA modeling developed could offer a method to predict the change of WVTR in correlation with cracking and delamination in the barrier thin film.

The aim of this work is, using finite element analysis, to study the effects of thermal load and rotation speed on the structural integrity of a substrate holder module in an MOCVD reactor. Several loading conditions are considered, including thermal load and rotational speeds of 0-1500 rpm. In addition, the wafer bow and residual stress of GaN film grown on silicon or sapphire wafer are systematically studied. Simulation results indicate the variation of critical stress with rotation speed in all of the components is small. Given a similar heat source in the MOCVD reactor, temperature of the upper components such as susceptor, substrate holders, and wafers is higher in the case of sapphire wafer than that in the case of silicon wafer. The temperature gradient of upper components is greater for the silicon wafer case. A greater temperature gradient in the film-substrate system generates a greater wafer bow and residual stress in the grown thin film. Therefore, temperature uniformity is an important parameter for the epitaxial process. The sign of residual stress is different between a GaN film grown on a sapphire wafer and a silicon wafer (compressive for sapphire wafer and tensile for silicon wafer). For growing a GaN thin film, sapphire wafer is better than silicon wafer in terms of lessening cracking in film.

This paper investigates mechanical behaviour and failure process of a 3D notched plate subjected to uni-axial tension using the discrete element method (DEM). The 3D notched plate consisted of different crystal structures, such as simple cubic (SC), body-centered cubic (BCC), face-centered cubic (FCC) and hexagonal close-packed (HCP), where constituent spheres were bonded together by contact bond. The inclination angle of the notch ranged from 0° to 90° with an increment of 15°. The aim of this study is to explore the effects of crystal packing and notch inclination angle on the mechanical responses, crack initiation and propagation, and crack paths. The proposed DEM model was first verified for the pre-cracking behaviour by the corresponding FEM calculation, and was confidently used to study the post-cracking behaviour. Numerical results reveal that the crack initiation and propagation of crystal structures depend on the crystal configuration and notch inclination angle. The loading stiffness of the four crystal structures follows the sequence of HCP > FCC > SC > BCC. The stress concentration factor shows a convex profile against notch inclination angle, with the maximum value at the notch inclination angle of 30° and the minimum value at the notch inclination angle of 90°. The SC and BCC crystal structures show a symmetric feature of crack propagation, whilst the FCC and HCP crystal structures exhibit asymmetric characteristics. In such a loading scenario, the crack initiation and propagation in all the four crystal structures are mainly dominated by the tension failure mode.

Fe-based alloys, such as ferritic stainless steels, developed for planar solid oxide fuel cell (pSOFC) interconnect commonly contain Cr and can form a chromia (Cr2O3) scale on the surface. At the high operating temperature of pSOFC, Cr can be oxidized to volatile Cr+6 species which can deposit in the cathode and lead to degradation of cathode performance and limit the lifetime of a pSOFC system. Coating a suitable material, such as lanthanum strontium manganite (LSM), has been practically conducted on the metallic interconnect to prevent such Cr poisoning in the cathode side of pSOFC. In this study, the joint strength between an SOFC glass-ceramic sealant (GC-9) and an interconnect steel (Crofer 22 APU) coated with La0.67Sr0.33MnO3 is investigated at room temperature (RT) and 800 °C in air under both shear and tensile loading modes. In particular, the effect of a long-term thermal aging at 800 °C on the joint strength is characterized. Results indicate that an LSM coating on the metallic interconnect degrades the joint strength between the given GC-9 glass-ceramic sealant and Crofer 22 APU interconnect steel. The shear strength at RT and 800 °C is significantly degraded by 36% and 65%, respectively, and the tensile strength is significantly reduced by 39% and 80% at RT and 800 °C, respectively. It is attributable to the existence of pores around the interface between GC-9 sealant and LSM coating. However, the shear strength of LSM-coated joint specimen is enhanced by 52% at RT and by 200% at 800 °C after 1000-h thermal aging in air. The given thermal aging treatment also improves the tensile strength of LSM-coated joint specimen by 50% at 800 °C. This may be attributed to a self-healing effect of the GC-9 glass-ceramic during thermal aging to reduce the pore size. Fractography analyses reveal that fracture path involving the LSM layer and its adjoining interfaces accompanies a lower joint strength.

An improved method based on fuzzy gain scheduling (FGS) control is developed in this study to tune the PID parameters and precisely control the working temperature in situ during laser cutting of non-oriented electrical steel sheets. Experiments on laser cutting of thin electrical steel sheets are performed to compare the cutting quality of kerf features using an open loop controller with a constant power, a conventional PID controller, and the proposed FGS controller. An unstable and inconsistent cutting quality of kerf with a larger heat affected zone (HAZ) and dross attachment is observed under open loop control due to a significant variation of working temperature and kerf width along the cutting path. The FGS controller shows better cutting performance and tracking response than the conventional PID controller by reducing the settling time as well as enhancing the control stability in the steady period. A better quality of finer and uniform kerf width with parallel kerf edges of a smaller HAZ and dross attachment are thus produced by the improved FGS control through real-time tuning of control parameters. Finally, the average kerf width is well correlated with the set-point temperature in FGS control by a linear equation.

An innovative method, step-controlled casting process (SCCP), was developed to produce LiAl alloy in mass production, which was potential for hydrogen storage. Formerly, the large difference in melting points between Li and Al was considered as a disadvantage to produce LiAl alloy. However, this disadvantage was overcome by SCCP. Characterization of as-cast specimens were performed using X-ray diffraction (XRD), inductively coupled plasma-atomic emission spectroscopy (ICP-AES), optical microscopy (OM), revealing that single phase LiAl alloy was successfully fabricated by SCCP with 94% yield. The hydrogen storage properties were also investigated by temperature-programmed decomposition (TPD) and XRD. The highest maximum hydrogen storage capacity reached 2.4 wt.% of the ball milled LiAl alloy when hydrogenated under 65 atm at 400 °C.

Following the previous companion paper, the proposed DEM model has been carefully validated and produced reasonable to good agreement with the corresponding laboratory experiments. This paper confidently probes the internal physical properties and extensively understands the multi-scale (macro-meso-micro scale) relationships in this granular system subjected to confined compression. The particle von Mises stress was proposed to effectively identify the direction and magnitude of strong force chains. Ring measurement cells were developed to calculate the spatial distributions of solid fraction, coordination number, friction mobilized factor, contact force vectors and stresses. The diagrams of contact force vectors were proposed to show the mechanism of force transmission onto the cylindrical wall. In addition, the statistical analyses for contact forces and mobilized friction were evaluated in this paper. Several key findings are highlighted as follows: (1) the force drop in the load–displacement response is attributed to some local reorganization of force chains; (2) the profiles of the contact force vectors transmitted onto the cylindrical wall match with those for macroscopic wall traction; (3) the contact force vectors on the cylindrical wall are mostly parallel with each other and make a specific angle with the horizontal, indicating the full friction mobilization on the cylindrical wall; (4) the inter-particle friction is more mobilized at the lower part than at the higher part during confined compression; (5) the radial, circumferential and vertical stresses within the bulk solid generally decay with depth in spite of some disorder; (6) The inter-particle and particle-wall contacts exhibit distinctive statistical patterns for contact forces and mobilized friction; (7) the mechanical response of this compressed granular system is transversely isotropic; (8) the contact forces are directed more vertically with depth, making the macro lateral pressure ratio decrease with depth.

Effects of cyclic deformation and annealing treatment on conductive durability of indium tin oxide (ITO) thin film deposited on polyethylene terephthalate (PET) substrate are investigated. In-situ electrical and mechanical tests of ITO/PET sheet under various combinations of cyclic and static loadings are conducted at room temperature. Experimental results show that the number of cycles to failure is significantly decreased with an increase in displacement amplitude, given a specific extent of electrical resistance change of ITO/PET sheet. A static holding period of 1000 s in various loading modes plays a role in influencing the failure of ITO/PET sheet. Cyclic bending combined with a static tensile holding generally generates more damages and a smaller number of cycles to failure than does that combined with a compressive holding, neutral holding, or no holding. Under a small fatigue loading, the conductive durability of ITO/PET sheet is increased with an increase in annealing temperature. However, there is little effect of annealing temperature on ITO/PET fatigue life under a larger displacement amplitude of fatigue loading. Using a surface-based cohesive modeling technique, a simplified three-dimensional finite element analysis micromodel subjected to tensile and compressive loadings is numerically analyzed to clarify the failure mechanism of interfacial and buckling-like delamination which governs the change in electrical conductivity of ITO/PET sheet. Modeling results indicate that buckle height of the ITO/PET micromodel subjected to tensile loading is significantly greater than that of compressive loading, providing more evidence of the aforementioned effect of loading mode.

Cracking behavior of positive electrode-electrolyte-negative electrode (PEN) assembly in a planar solid oxide fuel cells (pSOFC) during thermal cycling are investigated by using a commercial finite element analysis (FEA). The stress intensity factor for various combinations of surface crack size of 1 μm, 10 μm, and 100 μm and shape of semi-circular and semi-elliptical at highly stressed regions in the PEN are repeatedly calculated at room temperature and steady stage for twenty cycles. Simulation results indicate the stress intensity factor is significantly decreased at room temperature and is slightly increased at steady stage with increasing number of cycle. However, all the calculated stress intensity factors during thermal cycling in the present investigation are less than the corresponding fracture toughness given in the literature.

Interaction between granular solids and boundary structures is a fundamental problem encountered in bulk solids handling and subsurface structural design. Current understanding of its mechanism has not been adequate for robust and economical engineering designs, especially for flexible boundary structures. A classic and essential example is uniaxial compression of dry granules in a deformable cylindrical container, where the response of the confined granules under axial loading and the load transmission to the contacting structure still remain not fully understood. This paper comparatively studies such a confined compression scenario using a newly developed numerical procedure (Linked DEM-FEM) and a conventional FEM approach. The examined system involved around 7700 polystyrene beads contained in an acrylic thin-walled tube supported at one rim and gagged by two end platens. The compression was applied by displacing one end platen at a constant rate while fixing the other. Characteristics of the compression system, including load-displacement response, force transmission to boundary structure, mobilised bulk wall friction coefficient, and stress distribution on the wall, were evaluated. The majority of the compared physical quantities show reasonable to good agreement, thus giving a convincing quantitative verification for both approaches.

Interfacial cracking in the joint between a glass-ceramic sealant and a metallic interconnect under thermal stresses is characterized for a prototypical planar solid oxide fuel cell (pSOFC) stack, using finite element analysis (FEA). A three dimensional FEA model is constructed for a multiple-cell stack to perform thermal stress analysis at both steady operation and shutdown stages and to locate the highly stressed region in each component. Stress intensity factor and energy release rate for fracture are calculated at the crack front of a crack placed at the highly stressed interfacial region between a glass-ceramic sealant and a metallic interconnect in the given pSOFC stack for each stage. The critical crack or defect size at the interface of the joint of glass-ceramic sealant and metallic interconnect in the given pSOFC stack is determined by comparing the calculated energy release rates with the experimental measurements of interfacial fracture energy of the glass-ceramic/metallic interconnect joint.