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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.

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.

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.

MUCH theoretical and experimental data are available on the strength and stiffness of tension joints with perforations. The object of the present paper is twofold: firstly, to summarize some relevant parts of existing data, and secondly, to present the results of recent tests which serve to illustrate some outstanding features of members tested to destruction.

This paper is concerned with a new proposal regarding the analysis of visco‐elastoplasticity and fatigue and is based on rheological‐dynamical theory. Due to the analogy between rheological model and dynamical model with viscous damping, it becomes obvious that inelastic response of members is essentially a dynamical problem. An analytical rheological‐dynamical viscoelasto‐ plastic solution of one‐dimensional longitudinal continuous vibration under loading and solution for the stress relaxation as unloading have been developed and used to obtain the fatigue limit of thin long bars. Rheologic behavior of the bar can be characterized by one parameter, like in a single‐degree‐of‐freedom spring mass system. In all inelastic strains time rate effects are always present to some degree. Whether or not their exclusion has a significant influence on the prediction of the material fatigue behavior depends upon several factors like: maximum absolute stress in the cycle, coefficient of asymmetry of cycle, creep coefficient, slope of the strain hardening portion of the stress‐strain curve, relative frequency and uniaxial yield stress. This paper provides description of dynamic magnification factor, relaxation of stress, stress concentration and the fatigue limit of thin long symmetrical bars.

The purpose of this paper is to develop a new improved solution and a new model to predict both shear and normal interfacial stress in simply supported beams strengthened with bonded prestressed FRP laminates by taking into account the fiber volume fraction spacing that play an important role on the interfacial stresses concentration.

The study has been conducted by using analytical approaches for interfacial stresses in plated beams. The analysis is based on the deformation compatibility approach where both the shear and normal stresses are assumed to be invariant across the adhesive layer thickness. In addition, an unrealistic restriction of the same curvatures in the RC beam and FRP panel commonly used in most of the existing studies is released in the present theoretical formulation.

To verify the analytical model, the present predictions are compared first with those of (Malek et al., 1998; Smith and Teng, 2001) in the case of the absence of the prestressing force; for the second time, the present method is compared with that developed by (Al-Emrani and Kliger, 2006; Benachour et al., 2008) in the case where only the prestressing force is applied. From the presented results, it can be seen that the present solution agree closely with the other methods in the literature.

The paper puts in evidence a new originality approach theory, taking into account the mechanical load, and the prestressed FRP plate model having variable fiber spacing which considers a strength rigidity and resistance of the damaged structures, which is one aspect that has not been taken into account by the previous studies.

PROFESSOR PUGSLEY was the first to have popularized the term ‘philosophy’ in connexion with airworthiness. Generally, unless structures are completely safe they are regarded as unsafe. A flying machine, however, can at best be only approximately safe. Hence the need for an a priori definition of safety. Not only is it necessary to make a statistically definable sacrifice of safety to obtain a machine which will fly at all, let alone lift an economical payload, but this sacrifice must be spread in a certain manner to give acceptable returns.

NOTWITHSTANDING the fact that there exists a considerable amount of literature published in various forms on the subject of brittle lacquers and their applications to a multitude of diverse problems a brief resume of some of the general principles involved would seem not to be out of place.

IN the design of aircraft structures for fatigue strength, it is as well to bear in mind that those parts most likely to give trouble fatigue‐wise are those wherein rivets or bolts have to react a load. The term ‘react’ is used here to distinguish this from the case where rivets or bolts arc used to hold the skin on the frame, etc., where the worst possible concentration of stress in terms of the nominal gross area will approach that of a hole in an infinitely wide sheet, or about 3·0. The riveted joint is more likely to approach that of a lug, which, for conventional rivet spacing and edge distance would be about 5½ in terms of gross stress. In other words, our working stress for a joint would be about one‐half the axial stress in a plain sheet with holes for the same life. Other things, such as normal loads and buckling, may alter this ratio somewhat.