Stress In Region Research Articles

Effect of laser additive repair on high cycle fatigue properties of TC17 titanium alloy

This paper investigates the influence of laser cladding (LC) on the phase distribution, microstructure, residual stress, microhardness, and high-cycle fatigue performance of TC17 titanium alloy. The experimental results are analyzed through microscopic characterization and fatigue tests, and the fatigue fracture mechanism is discussed. The LC process transforms the dual-phase α + β material containing stable β phase into a microstructure composed entirely of β phases. The β phases exhibit a coarse grain size up to 200 μm and numerous epitaxial columnar crystals in the additive direction. Near the laser cladding zone (LCZ), residual stress is in a tensile state, while the stress in the additive region relaxes to almost 0 after 106 cycles under a load of 300 MPa, without any change in the substrate's stress. Microhardness in the substrate, heat affected zone (HAZ), and LCZ shows a slight decrease trend, with only a 5 % drop. The fatigue limit of the TC17 repaired sample (309 MPa) decreases by approximately 45 % compared to the forging material (557 MPa) after 106 cycles at a stress ratio of 0.1. However, this result (309 MPa) is over 70 % higher than that of samples damaged by foreign objects (180 MPa), indicating a significant repair effect. Fatigue fracture observations reveal that cracks originate from additive manufacturing pores, and the crack propagation rate in the LCZ is significantly higher than that in the substrate. The characteristics of dimples in the final fracture region indicate a decrease in the plasticity of TC17 titanium alloy due to the additive repair.

Bond Wire Fatigue of Au, Cu, and PCC in Power LED Packages.

Bond wire failure, primarily wire neck breakage, in power LED devices due to thermomechanical fatigue is one of the main reliability issues in power LED devices. Currently, the standard testing methods to evaluate the device's lifetime involve time-consuming thermal cycling or thermal shock tests. While numerical or simulation methods are used as convenient and quick alternatives, obtaining data from material lifetime models with accurate reliability and without experimental fatigue has proven challenging. To address this issue, a mechanical fatigue testing system was developed with the purpose of inducing mechanical stresses in the critical region of the bond wire connection above the ball bond. The aim was to accelerate fatigue cracks at this bottleneck, inducing a similar failure mode as observed during thermal tests. Experimental investigations were conducted on Au, Cu, and Pd-coated Cu bonding wires, each with a diameter of 25 µm, using both low- and high-frequency excitation. The lifetime of the wire bond obtained from these tests ranged from 100 to 1,000,000 cycles. This proposed testing method offers material lifetime data in a significantly shorter timeframe and requires minimal sample preparation. Additionally, finite element simulations were performed to quantify the stresses at the wire neck, facilitating comparisons to conventional testing methods, fatigue test results under various operating conditions, material models, and design evaluations of the fine wire bond reliability in LED and microelectronic packages.

Geometric Conformability of 3D Concrete Printing Mixtures from a Rheological Perspective

The effectiveness of 3D concrete printing (3DCP) relies on understanding the rheological properties of cementitious materials and their time-dependent evolution. These materials exhibit shear-thinning viscosity, an elastic region, and both static and dynamic yield stress, which are challenging to balance in 3DCP. Layer deformation can be caused by factors such as self-weight, the weight of subsequently deposited layers, and the stress induced by the nozzle pressing. Starting at the level of a single filament, the final geometrical conformity of a 3D-printed object is the sum of individual filament conformities. Hence, the control of layer deformation during the printing process is critical. The failure of 3D-printed objects can occur due to two primary mechanisms: material failure, which occurs when the material’s strength is exceeded, resulting in fracture or uncontrolled deformation; and stability failure, where the object cannot retain equilibrium of forces. These mechanisms often interact; extensive deformations resulting from material failure can lead to stability loss, or conversely, stability loss generates local excessive stresses leading to material failure. The governing mechanism depends on various factors, including material and process characteristics, as well as the transient nature of material properties, print strategy, and object design. With this in mind, this research aimed to broaden the understanding of the connection between rheological material properties—primarily yield stress—and the geometric conformability of printed objects. Experimental tests were conducted on pastes using a rheometer, and correlated mortars, allowing for the evaluation of realistic extrusion properties.

Path analysis and logistic regression for heat tolerance in sheep

Climate change and increasing atmospheric temperature are important issues in breeding small ruminants. Although sheep animals are highly adaptable to extreme conditions, observing how they respond physiologically when challenged in stressful climatic regions is important. Understanding the physiological pathways that lead these animals to thermal equilibrium is crucial. The present study aimed to analyse the interaction between environmental and physiological variables on heat stress in different breeds of sheep by path and logistic regression analysis. In total, 16 sheep genetics groups were studied and classified into two groups (wool and hair) to analyse how the variables correlate using path analysis and the responses of respiration rate and rectal temperature to increased temperature and humidity index using logistic regression analysis. Suffolk and Dorper breeds presented alterations in respiration rate before the others. Bergamasca and Poll Dorset × Dorper were the first groups to demonstrate alterations in rectal temperature. Hampshire Down breed showed no alteration in respiration rate. Morada Nova was the breed (among the breeds with hair) with the more delayed respiration rate and rectal temperature alteration. The use of path analysis and logistic regression helps in the understanding of how sheep animals respond physiologically to environmental changes.

Analysis of the microscopic characteristics of periodic structure arrays on silicon carbide fabricated by femtosecond laser

The fabrication of large dimension structures (800 μm × 800 μm) featuring fine and coarse ripple patterns, nano particle structures, and V-shaped grooves was achieved on silicon carbide (SiC) through the use of femtosecond laser. The X-ray photoelectron spectroscopy (XPS), X-ray diffraction (XRD) and Raman spectroscopy (Raman) were performed on sample surface to investigate the atomic bond, residual stress and lattice disorder. XPS analysis revealed that an increase in laser fluence resulted in an increase in the content of C=O bond, while the content of O–C=O bond decreased. The C–C (sp2) bond was destroyed, while the unstable C–C (sp3) bond increased. Additionally, there was a decrease in the content of Si–Si bond and Si–C bond, and an increase in the content of Si–O bond. The resulting oxide layer contributed to an improvement in the fracture toughness of the periodic array. XRD analysis results indicate that the technique is not sensitive to structural defects in SiC and surface contaminants caused by laser ablation. On the (0008) crystal plane, an increase in fluence resulted in an initial increase in lattice spacing, strain, and residual stress, followed by a plateau. The laser-modified area corresponded to a region of tensile stress, with the maximum tensile stress being 179.464 MPa. On the (0004) crystal plane, an increase in fluence resulted in varying degrees of increase in lattice spacing, strain, and residual stress. The residual tensile stress at the fine ripple and groove bottom was 0 and 14.623 MPa, respectively, while the residual tensile stress at the coarse ripple and nano particle structure was 277.847 MPa. The residual tensile stress increased with an increase in scanning interval. Raman analysis showed that the overall disorder increased with an increase in laser fluence, with a maximum degree of disorder being 0.548.

In-plane dynamics crushing of a reinforced honeycomb with enhanced energy absorption

Recently, an increasing interest in reinforced honeycomb structures (RHC) due to their exceptional mechanical properties and potential applications in energy absorption. This paper focuses on the theoretical and numerical study of the in-plane dynamic crushing response of RHC and the reinforced honeycomb structure with one layer of reinforcement and one layer of non-reinforcement(1 + 1RHC). The 1 + 1RHC was fabricated with a welding method. A displacement-controlled in-plane compressive load was applied to the 1 + 1RHC specimens. Three different deformation modes were monitored at varying impact velocities: low-speed, medium-speed, and high-speed modes. The deformation modes maps were developed to reveal the extent of effects by impact velocity and relative density. For 1 + 1RHC, two distinct plateau stress regions were identified at low-velocity impact loading. Additionally, the first plateau stress value of the 1 + 1RHC structure is 180.4% higher than that of structures with two platform stresses, and the second platform stress value is 71.0% higher than that of structures with two platform stresses. The 1 + 1RHC structure exhibits superior energy absorption and negative Poisson's ratio performance. The paper also discusses the impact of cell wall thickness, angle, and velocity on the crushing strength of both RHC and 1 + 1RHC. The results obtained by theoretical methods align well with that obtained from finite element simulations.

Optimum test condition setting and sample allocation for accelerated degradation tests under the last-exit-time failure mode

ABSTRACT Accelerated degradation tests (ADTs) have been widely adopted for products whose failure is defined as the first-passage-time (FPT) when the degradation path crosses a given threshold. However, for products whose failure is defined as the last-exit-time (LET), few studies related to ADT have been investigated. In this paper, we focus on designing an optimum test condition setting and sample allocation scheme for ADTs under the LET failure mode. In particular, the widely adopted Wiener process model and the generalized exponential acceleration model are used to describe the fluctuating degradation behaviors of products. By minimizing the asymptotic variance of mean-time-to-failure under the normal use condition, we design a two-level optimum test plan and a three-level compromise plan under the constraints of total sample size and stress region. The optimum plans are given in analytical forms, and we prove that the optimum plans under the FPT failure mode and LET failure mode are equivalent under some situations. Finally, a renewed selection method for the upper limit of the stress level in ADTs is proposed based on the prior ADT information from the perspective of accelerated mechanism equivalence. The proposed method is illustrated using a real-world application to rubber rings.

Depth profiling of residual stress distribution in surface treated metallic structures using nonlinear ultrasonics

Robotic hammer peening (RHP) is a cold-working technique to improve the fatigue life of metallic structures by inducing compressive residual stress in the near-surface region. Measuring the depth profiling of residual stress distribution plays an important role in process design towards the advanced manufacturing of metallic structures. This study investigates the use of the nonlinear ultrasonic method to measure the residual stress profiles through the frequency-dependent penetration depth approach. Stainless steel specimens were treated with varying RHP intensities, and their morphological evolutions were characterized with a step-profilometer. The amplitudes of the second and third harmonic components of the longitudinal critically refracted (LCR) and Rayleigh waves were measured and analyzed. The effect of the surface roughness on the acoustic nonlinearity parameters before and after polishing at various peening intensities was briefly discussed. The results show a large variation in the acoustic nonlinearity parameter at the surface layer, indicating the potential of the proposed nonlinear ultrasonics for the measurement of depth profiling of residual stress.

Prediction and demonstration of periodic tensile cracking in rate-dependent porous cement

Periodic tensile cracks are shown to occur when cylinder-shaped saturated cement specimens are subjected to rapid decompression, with the spacing between the cracks scaling as a power law of the decompression time. This behavior is predicted by theory, which is specified to this scenario based on prior work that was more general and applied to compaction bands. Specifically, the formation of the tensile cracks is shown to coincide with periodicity that naturally arises in the effective stress when the material follows a Terzaghi-type consolidation law, although in reverse for dilation and with material deformation described by a rate-dependent viscoplastic law. When strain rate is proportional to effective stress to a power that is greater than one, periodic regions of tensile effective stress arise through the poromechanical fluid–solid coupling. The theoretically-predicted exponent of the resulting power-law relationship between tensile cracks spacing and unloading time successfully brackets the experimental results, for which it is observed that the exponent is slightly stronger than a square-root relationship (0.28 to 0.67) at testing temperatures of 20 ℃ and 90 ℃. These results demonstrate that rapid-depressurization leads to periodic fracturing that could, on the one hand, be detrimental to the isolation provided by cement used to seal wellbores in the petroleum industry. On the other hand, the periodic tensile cracks could also be favorable to production if generated in low-permeability reservoir rocks such as shales that are targeted for petroleum production or granites that are targeted for geothermal energy.

Dynamic modeling and analysis of fluid-delivering cracked pipeline considering breathing effect

Crack is the most common failure mode of the pipeline system, which may lead to high-speed and high-pressure hydraulic oil leakage. In this paper, the dynamic modeling and model order reduction methods for the fluid-delivering cracked pipeline (FDCP) considering the breathing effect are proposed, and the structural intensity method (SIM) is introduced to visualize the vibration transmission and breathing effect of FDCP. The fluid, solid, and coupling elements are constructed to establish the dynamic model of FDCP, the spring element is used to simulate the breathing effect, the dynamic substructure method is extended to perform the model order reduction of FDCP, and the rationality of the modeling method is verified by experiments. SIM and energy principles are used to visualize and analyze the vibration transmission of FDCP. The analysis results show that the natural frequencies are sensitive to the cracks in the maximum modal displacement and stress regions, and the fluid velocity and pressure (FVAP) will enhance the breathing effect of FDCP. In addition, the vibration transmission analysis can accurately detect the crack with different damage degrees, and FVAP do not influence the vibration transmission laws. The modeling and analysis method in this paper can provide a theoretical reference for fault diagnosis of FDCP.

Biomechanical Analysis of Titanium Dental Implants in the All-on-4 Treatment with Different Implant-Abutment Connections: A Three-Dimensional Finite Element Study.

The type of implant-abutment connection is one of the factors influencing the distribution of occlusal forces. This study aims to investigate the biomechanical performance of the mandibular all-on-4 treatment with different implant-abutment connections. Two connection types with 30° abutments and 18-mm implant fixtures were chosen for the posterior implants of the all-on-4 assembly. For the external hexagon connection (EHC) group, the implants with 4 mm in diameter were used. For the internal hexagon connection (IHC) group, we selected implants with 4.3 mm in diameter. A vertical force of 190 N was applied to the cantilever region. The FEA results indicated that the most stressed region in the two groups was prosthetic screws, followed by multi-unit abutments (MUAs). The lowest values of von Mises stress were both observed on the bone. The peak stress value of the implant screw and implant fixture in the EHC group were 37.75% and 33.03% lower than the IHC group, respectively. For stress distribution patterns, the load force tended to be concentrated at locations where components were interconnected. The EHC and IHC are clinically durable under the tested loading conditions, but the prosthetic screws and MUAs can be the weak point on the posterior implant within the mandibular all-on-four assembly. The peak stress values of implant screw and implant fixture in the EHC groups were lower than the IHC group.

Tolerance to deformation and flux pinning in superconducting amorphous molybdenum nitride thin films grown on flexible polyimide

We investigate the superconducting properties of 80 nm thick amorphous MoNx films fabricated via reactive sputtering on silicon and flexible commercial polyimide substrates. The samples are grown at room temperature using reactive sputtering with a gas mixture of N2 and Ar. The mechanical deformation tolerance for films on polyimide is evaluated by comparing the superconducting critical temperature (Tc) and critical current density (Jc) when the films are attached to cooper surfaces with varying curvatures. The amorphous films exhibit a Tc of 8.2 K on silicon and 7.9 K on polyimide. Our results demonstrate a significant enhancement in flux pinning for the thin films grown on polyimide, with the Jc at self-field and 3 K increasing from approximately 0.5 MA/cm2 to around 1 MA/cm2. Analyses of Jc as a function of the magnetic field, angle, and temperature reveal that the films on polyimide exhibit remarkable resilience to deformation. Interestingly, comparable Jc values are observed when the samples are affixed to both flat and cylindrical surfaces with diameters of 2.5 cm. This observation suggests that vortex dissipation predominantly occurs through flux motion in the region experiencing the maximum Lorentz force. Furthermore, the films maintain Tc without any discernible changes in resistivity when fixed to cylindrical surfaces with 1.2 cm diameters. However, there is a significant drop in vortex pinning, indicating reduced pinning capability in the stressed regions. The high deformation tolerance of amorphous MoNx renders it highly suitable for cryogenic electronics applications, providing a viable alternative to the commonly utilized metallic Nb.

Morphological responses of three contrasting Soybean (Glycine max (L.) Merrill) genotypes under different levels of salinity stress in the coastal region of Bangladesh

Soil salinity, a global environmental issue, inhibits plant development and production. Soybean is an economically important legume crop whose yield and quality are highly affected by excessive levels of salt in the root zone. A factorial experiment was conducted in a net house from October 2019 to January 2020 to evaluate the performance of three distinct soybean genotypes under varying levels of salinity stress. The experiment followed a completely randomized design (CRD) with three replications. Three soybean cultivars, namely BINA Soybean 1, BINA Soybean 2, and BINA Soybean 4 were used in this experiment. The soil salinity treatments were 0 mM NaCl, 50 mM NaCl, 100 mM NaCl, 150 mM NaCl, and 200 mM NaCl. The electrical conductivity (EC) of the soil sample was 0.91dS/m. Six seeds were sown 3 cm deep in each pot. A total of 45 pots were used in this experiment. The performance of each variety was evaluated based on its germination percentage, time of germination, no. of branches/plant, no. of leaves/plant, no. of flowers/plant, plant height (cm), no. of pods/plant, pod length (cm), seeds/pod, and root length (cm). Based on the results obtained from this research trial, it can be inferred that the BINA Soybean 2 variety along with 0 mM NaCl, 50 mM NaCl, and 100 mM NaCl treatments exhibited superior performance in all parameters compared to the other varieties. This study provides clear evidence that the soybean, particularly the BINA Soybean 2 variety, holds significant promise as a crop suitable for coastal regions. Furthermore, it suggests that the cultivation of soybeans in such areas could potentially enhance agricultural productivity, particularly in the presence of mild saline conditions. Nevertheless, it exhibits limited growth potential in environments with elevated salinity levels.

Predicting degradation of composite-titanium adhesively bonded joints exposed to seawater environment

In this paper, focusing on the composite-titanium adhesively bonded structures aging in seawater environment, a prediction method coupling the experiments, theoretical model and numerical simulation for degradation of the tensile behavior of adhesively bonded joint was proposed. Bulk adhesive and fracture specimens were aged in 45 ℃ artificial seawater to characterize the adhesive moisture absorption behavior and degraded fracture properties, respectively. Based on the discrete experimental degraded fracture properties, a theoretical continuous water coupled fracture model for the prediction of degraded fracture properties was developed. The theoretical model can predict the degraded fracture toughness based on the moisture. Prediction of the degraded tensile properties of single-lap adhesively bonded joint was conducted. The predicted tensile strength of the aging specimen agreed well with the experimental results, with less than 5 % error. Moreover, spatial variations of the damage and stress of the aging adhesive layer can be predicted by the prediction method coupling the moisture absorption. The predicted results indicated that the damage value and area of the width edge of the adhesive layer were both greater than central region, and the predicted peak stress in the central region was nearly 33.2 MPa while that of the edge decreased to 12.5 MPa.

Global land subsidence mapping reveals widespread loss of aquifer storage capacity

Groundwater overdraft gives rise to multiple adverse impacts including land subsidence and permanent groundwater storage loss. Existing methods are unable to characterize groundwater storage loss at the global scale with sufficient resolution to be relevant for local studies. Here we explore the interrelation between groundwater stress, aquifer depletion, and land subsidence using remote sensing and model-based datasets with a machine learning approach. The developed model predicts global land subsidence magnitude at high spatial resolution (~2 km), provides a first-order estimate of aquifer storage loss due to consolidation of ~17 km3/year globally, and quantifies key drivers of subsidence. Roughly 73% of the mapped subsidence occurs over cropland and urban areas, highlighting the need for sustainable groundwater management practices over these areas. The results of this study aid in assessing the spatial extents of subsidence in known subsiding areas, and in locating unknown groundwater stressed regions.

Yield stress prediction from 3D reconstruction of fresh concrete slump

Relating the empirical slump test to yield stress facilitates the capture of fresh state concrete performance in fundamental quantitative terms whilst avoiding the requirement for expensive rheological equipment. This paper proposes a novel method to predict yield stress from slump by directly measuring the height of the unyielded region, via a 3D reconstruction approach. The efficacy of the proposed method is assessed through an experimental series of 21 tests. The results indicate a better correlation between the height of the unyielded region and yield stress compared to total slump height and yield stress. The proposed 3D reconstruction methodology predicts yield stress with significantly increased accuracy, indicated by a mean prediction error an order of magnitude lower than the average performance of existing models. The results of this study suggest that, for the first time, a valuable fundamental rheological property can be confidently derived from a standard concrete slump test.

Design and Analysis of Brake Drum using Finite Element Analysis

Because of the need for safety, braking performance has become a very important factor for automotive manufacturers and passengers. Despite all the stresses experienced by the drum brake doesn’t damage the drum due to high tensile strength but the drum may fail under fatigue loading. The critical region of concentrated stress is determined, and appropriate modifications are being made to improve it. The distribution of stress and the heat dissipation obtained from the result of the analysis are employed as input for the failure region. The findings of stress and thermal analysis are crucial for improving the component design at the first stage of development. The objectives of this study are to modify and improve the circumferential strength and heat dissipation and to optimize the design of the drum brake with simulation using Finite Element Analysis. The simulation was run on the initial model and modified on its to make it better. it shows that 27.33% decrease in maximum von Mises stress. Thermal analysis for heat flux on the material will show the ability of heat dissipation. Overall, It has been determined that aluminium alloy is the optimum material for drum brake design in terms of total heat flux.

Investigation on bond behavior of steel-FRP composite bars in engineered cementitious composites by spliced beam tests

The collaborative utilization of steel-FRP composite bar (SFCB) and engineered cementitious composites (ECC) represents a favorable choice for engineering structures exposed to aggressive environments, offering benefits involving both mechanical behavior and durability. This paper primarily studies the bond performance of SFCB embedded in ECC through spliced beam tests coupled with finite element analysis. The findings demonstrate that with an appropriate cover thickness or transverse confinement, spliced ECC beams exhibit failure modes characterized by splitting and pull-out. Under such conditions, the bond-slip response demonstrates limited sensitivity to changes in cover thickness and transverse confinement. Conversely, increasing the cover thickness or introducing transverse confinement in spliced concrete beams, which exhibit splitting failure, significantly enhances the bond strength. Furthermore, in contrast to spliced concrete beams, spliced ECC beams are observed to demonstrate a bond toughness that is 3.85–12.10 times greater. The discrepancy in bond toughness between ECC and concrete diminishes as the cover thickness and transverse confinement increase. Notably, the uniform distribution of bond stress in the splice region of ECC beams remains unaffected by variations in splice length. To incorporate the impact of bond stress distribution when calculating the splice length of SFCB in ECC beams, a coefficient of 0.85 is introduced.

Evaluation of Anisotropic Biaxial Stress in Extremely-Thin Body (100) Silicon-Germanium-on-Insulator p-Type Metal-Oxide-Semiconductor Field-Effect-Transistor by Oil-Immersion Raman Spectroscopy

We evaluated the anisotropic biaxial strain in the channel region of extremely-thin body silicon-germanium-on-insulator p-MOSFETs by oil-immersion Raman spectroscopy. Oil-immersion Raman spectroscopy can measure the transverse optical (TO) phonon mode which cannot be detected by conventional Raman spectroscopy under the backscattering configuration for (001) substrate. Therefore, we can calculate the anisotropic biaxial stress in the SiGe channel region and investigate the channel width dependence of stress. From the Raman spectra obtained in the polarization configurations of longitudinal optical (LO)-active and TO-active, we confirmed that compressive stress is induced in the SiGe channel region. In addition, we observed that the strain state of the SiGe channel region becomes quasi-uniaxial strain by narrowing the channel width.

Effects of cooling roofs on mitigating the urban heat island and human thermal stress in the Pearl River Delta, China

The Weather Research and Forecasting model was employed to simulate the effects of cooling roofs on the urban heat island effect and human thermal stress in the Pearl River Delta region, China, in summer (June–August) 2014. It was found that cooling roofs can reduce the 2-m air and ground-surface temperature, wind speed, and planetary boundary layer height, while increasing the specific and relative humidity, in urban areas. The effects can influence the entire urban boundary layer, especially in commercial/industrial areas in the daytime. Cooling roofs can effectively mitigate the urban heat island effect, and the mitigation of white roofs is more significant than that of green roofs. The mitigation of the urban heat island effect is stronger in commercial/industrial areas than in low-intensity residential areas. The city-wide 2-m and ground-surface urban heat island intensity induced by white roofs can reduce by 1.5 °C and 4.8 °C at noon, while the corresponding decreases induced by green roofs can reach 0.7 °C and 1.9 °C, respectively. White roofs improve human thermal comfort both in the daytime and at nighttime. With white roofs, three city-wide thermal-stress indices (wet-bulb globe temperature, apparent temperature, and humidity index) can be reduced at noon by 0.8 °C, 1.3 °C and 1.5 °C, respectively. Green roofs mostly improve human thermal comfort at nighttime but even deteriorate it in the daytime. The above three indices decrease by less than 0.5 °C in different urban categories at nighttime with green roofs.