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Social stress is a psychological and biological pressure that stems from one's relationship with others in social environments, which has become the most serious humanitarian issue today. Learning environments are one of the most important environments for reducing or increasing social stress and concentration. This study aims to investigate the effect of classroom wall color on students' stress and concentration in four common types of classrooms.

This research is a survey of 275 university students with an age range of 20–24. The methodology is a combination of quantitative and qualitative research. Data analysis was performed by multiple variance analysis and the internal reliability of the questionnaire was calculated based on Cronbach's alpha.

Results show that classroom wall color has a significant effect on student stress and concentration. In class type one, wall color had an effect of 10.4% on stress and concentration; in the second type, this variable had an effect of 8.8%, also in the third type it had an effect of 7.3% and 8.8% in the fourth type.

It can be concluded that wall color has an effective role in understanding the level of stress and concentration of users in the classrooms, and considering this factor in designing classrooms improves students' behavior and the quality of education in learning environments.

In order to obtain the relationship between the geometry and stress concentration of load-bearing welded joints, the fatigue design method of welded structures based on stiffness coordination strategy is studied.

Based on the structural stress theory, a new method for anti-fatigue design of welded structures oriented to stiffness coordination strategy is proposed, and the detailed implementation process of this method is given. This method is also called the three-stage anti-fatigue design method for welded structures, which includes three stages, namely, identification, analysis and relief of stress concentration.

Through the experimental analysis of welded joints in IIW standard, the effectiveness of stiffness coordination in welded joint design is proved. The method is applied to the design of welded parts and products, and the feasibility of the method in alleviating the phenomenon of stress concentration and improving the fatigue resistance of welded structures is verified.

In this study, based on the principle of coordinated design of weld stiffness, a three-stage anti-fatigue design method of welded structure is proposed. The method has practical value for the optimization design and anti-fatigue performance improvement of welded structure in engineering products.

Inverse distance weighted (IDW) functions are utilized to make models of heterogenous materials such as functionally graded materials (FGM) in computer aided design (CAD). However, the use of IDW function based FGM for stress concentration reduction is scarcely available in the literature. The present work aims to analyze and reduce the stress concentration around a circular hole in IDW function-based finite FGM panel under biaxial loading.

Extended finite element method (XFEM) model was prepared using MATLAB to investigate the effect of geometrical and material parameters on the stress concentration factor (SCF). The obtained results of IDW FGM are compared with homogeneous material as well as two different FGMs based on the power-law function.

It was observed that the IDW function based FGM is simple in material modeling, conformal with all domain boundaries and shows lower stress concentration in comparison with the homogeneous material case. While comparing IDW FGM with power-law based FGMs, it was observed that the IDW FGM has least values of stress concentration for low d/W (diameter of the hole to panel width ratio) and is comparable with power-law based FGMs for high d/W.

It can be stated that IDW FGM is highly suitable for stress concentration reduction in finite panels with d/W = 0.5, which can further be intended for obtaining optimum hole and panel designs.

The purpose of this paper is to evaluate the effect of film cooling holes on the vibration characteristics of a turbine blade, and provide the design basis for the blade, which may reduce computing costs.

Modal analysis of the blades with and without film cooling holes is performed to evaluate the effect of film cooling holes on its natural frequency. Harmonic analysis of the blade is performed to calculate the stress concentration factors of film cooling holes for different modes.

The frequency differences between two blades with and without film cooling holes are insignificant, while the differences of the vibration stress cannot be neglected. For the first three modes of the blades, the stress concentration factor is sensitive to the hole’s shape and position on the blade. With the help of the stress concentration factor defined in this work, the concentration of stresses induced by different film cooling holes can be accurately described when evaluating HCF life of the turbine blade.

The effect of film cooling holes on a turbine blade's natural frequencies was confirmed to be insignificant and the stress concentration factors around the holes are calculated. Therefore, the simplified model of the blade without film cooling holes can be used to evaluate the natural frequencies and vibration stress, which saves a lot of time and cost.

The stress state near the notch affects fatigue damage directly, but quantifying the stress field is difficult. The purpose of this study is to provide a mathematical description method of the stress field near the notch to achieve a reliable assessment of the fatigue life of notched specimens.

Firstly, the stress distribution of notched specimens of different materials and shapes under different stress levels is investigated, and a method for calculating the stress gradient impact factor is presented. Then, the newly defined stress gradient impact factor is used to describe the stress field near the notch, and an expression for the stress at any point along a specified path is developed. Furthermore, by combining the mathematical expressions for the stress field near the notch, a multiaxial fatigue life prediction model for notched shaft specimens is established based on the damage mechanics theory and closed solution method.

The stress gradient factor for notched specimens with higher stress concentration factors (V60-notch, V90-notch) varies to a certain extent when the external load and material change, but for notched specimens with relatively lower stress concentration factors (C-notch, U-notch, stepped shaft), the stress gradient factor hardly varies with the change in load and material, indicating that the shape of the notch has a greater influence on the stress gradient. It is also found that the effect of size on the stress gradient factor is not obvious for notched specimens with different shapes, there is an obvious positive correlation between the normal stress gradient factor and the normal stress concentration factor compared with the relationship between the shear stress gradient factor and the stress concentration factor. Moreover, the predicted results of the proposed model are in better agreement with the experimental results of five kinds of materials compared with the FS model, the SWT model, and the Manson–Coffin equation.

In this paper, a new stress gradient factor is defined based on the stress distribution of a smooth specimen. Then, a mathematical description of the stress field near the notch is provided, which contains the nominal stress, notch size, and stress concentration factor which is calculated by the finite element method (FEM). In addition, a multiaxial fatigue life prediction model for shaft specimens with different notch shapes is established with the newly established expressions based on the theory of damage mechanics and the closed solution method.

It is well known that notches have a deleterious influence on the fatigue strength of parts. A constant, the sensitivity index, is commonly used to relate the fatigue stress concentration factor to the elastic stress concentration factor. The author outlines a simpler hypothesis, which he claims to be a more reliable guide to fatigue behaviour in notches. Briefly it assumes that the elastic stress concentration factor gives the reduction in the fatigue strength due to the notch, but because of the local nature of the stress concentration, the endurance limit is increased according to a simple law. This increase in the fatigue strength depends on the smallness of the notch.

The purpose of this study was to investigate the effect of overload (bending moment with plastic deformation: Mp) on three point bending specimen at the fatigue limit of high-tensile-strength steel containing a crack in the stress concentration zone.

An artificial semi-circular slit was introduced and Mp was applied after which bending fatigue tests were carried out.

The relationship between the level of Mp and the fatigue limit (σ_w) was proportional; the fatigue limits of specimens containing 0.2- and 0.3-mm-deep slits are improved by the Mp process as much as twice the original values; the slit size that can be rendered harmless by the Mp process is a=0.05 mm in depth; and all non-propagating cracks appeared around the artificial slit.

Very few studies have been conducted on the fatigue limit of materials containing crack-like surface defects after overload in the stress concentration zone. This study elucidated the effect of Mp on the fatigue limit.

This paper aims to use an imidazole-based n-ionic Gemini surfactant derived from palm oil to inhibit the sulfide stress corrosion cracking of a supermartensitic stainless steel.

The slow strain rate testing technique, hydrogen permeation tests and potentiodynamic polarization curves have been used.

Addition of the inhibitor below the critical micelle concentration (CMC) decreased the corrosion current density (i_corr), but not enough to avoid embrittlement due to the entry of hydrogen into the steel. Instead, the addition of the inhibitor close to the CMC decreased the i_corr, suppressed the entry of hydrogen and inhibited the sulfide stress cracking of steel. Finally, the addition of inhibitor above the CMC led to a slight increase of i_corr and promoted localized corrosion, however, the sulfide stress cracking of steel was inhibited.

A green sulfide stress corrosion cracking inhibitor of a supermartensitic stainless steel has been obtained.

The purpose of this paper is to estimate the acceptable defect size amax after needle peening (NP) and predict the fatigue limit improvement through the use of NP for an austenitic stainless steel welded joint containing an artificial semi-circular slit on a weld toe.

Residual stress and hardness distribution were measured. Microstructures around the weld toe were observed to clarify the cause for the change in hardness after NP. Finite element method analysis was used to analyze the change in the stress concentration following NP. Fracture mechanics was used to evaluate amax after NP. The fatigue limits before and after NP were predicted by determining amax for several levels of stress amplitude.

The tensile residual stress induced at the surface of the weld toe prior to NP changed to a compressive residual stress after NP. The residual stress near the surface layer after NP exceeded the yield stress prior to NP due to the increase in yield stress as a result of work hardening as well as the generation of a deformation-induced martensitic structure. The stress concentration was reduced due to the shape improvement caused by NP. The estimation value of amax after NP and the prediction results of fatigue limits were in good agreement with the fatigue test results.

The proposed method is useful in improving the reliability of welded joints used in large steel structures, transportation equipments and industrial machines.

From an engineering perspective, it is essential to estimate amax and the fatigue limit of welded joints with crack-like defects. However, it is unclear as to whether it is possible to predict amax and the effects of NP on the fatigue limit for stainless steel welded joints.

This paper aims to present the novel stacked machine learning approach (SMLA) to estimate low-cycle fatigue (LCF) life of SAC305 solder across structural parts. Using the finite element simulation (FEM) and continuous damage mechanics (CDM) model, a fatigue life database is built. The stacked machine learning (ML) model's iterative optimization during training enables precise fatigue predictions (2.41% root mean square error [RMSE], R² = 0.975) for diverse structural components. Outliers are found in regression analysis, indicating potential overestimation for thickness transition specimens with extended lifetimes and underestimation for open-hole specimens. Correlations between fatigue life, stress factors, nominal stress and temperature are unveiled, enriching comprehension of LCF, thus enhancing solder behavior predictions.

This paper introduces stacked ML as a novel approach for estimating LCF life of SAC305 solder in various structural parts. It builds a fatigue life database using FEM and CDM model. The stacked ML model iteratively optimizes its structure, yielding accurate fatigue predictions (2.41% RMSE, R² = 0.975). Outliers are observed: overestimation for thickness transition specimens and underestimation for open-hole ones. Correlations between fatigue life, stress factors, nominal stress and temperature enhance predictions, deepening understanding of solder behavior.

The findings of this paper highlight the successful application of the SMLA in accurately estimating the LCF life of SAC305 solder across diverse structural components. The stacked ML model, trained iteratively, demonstrates its effectiveness by producing precise fatigue lifetime predictions with a RMSE of 2.41% and an “R²” value of 0.975. The study also identifies distinct outlier behaviors associated with different structural parts: overestimations for thickness transition specimens with extended fatigue lifetimes and underestimations for open-hole specimens. The research further establishes correlations between fatigue life, stress concentration factors, nominal stress and temperature, enriching the understanding of solder behavior prediction.

The authors confirm the originality of this paper.