Effect Of Stress Concentration Factor Research Articles

Stress concentration affecting hydrogen-assisted crack in API X70 pipeline base and weld steel under hydrogen/natural gas mixture

A sudden change in the geometrical parameters of a material, such as bends, T-branches, and welded joints may increase the stress concentration, which in turn may enhance the diffusible hydrogen concentration. In this study, quantitative evaluations of the effect of stress concentration factors on hydrogen environmental embrittlement (HEE) will be studied based on the mechanical performance of notched tensile specimens with variations in the stress concentration factors (Kt) of the X70 pipeline base and weld metal. To highlight the role of stress concentration, the tests are performed under a 10 MPa gas mixture condition with a low partial hydrogen pressure. The maximum strengths of the notched specimens were nearly consistent across all Kt values. The degree of HEE susceptibility of the base metal increased with increasing Kt value. However, in the weld metal, prominent reductions in the RA occurred at all Kt values. The complex HEE susceptibility of the weld metal can be attributed to the synergistic action of the microstructure heterogeneity and Kt values.

Experimental and Numerical Investigation of Stress Concentration Factor of Cable Steel Wire with Corrosion Pits

Fatigue crack initiates from corrosion pits in various metallic structures, leads to the decline of the fatigue life. In the present study, the effects of the width, depth, angle and spacing of primary and secondary pits on failure mechanism and stress concentration factor are investigated by the experimental and numerical analysis. The results show that depth-width ratio of corrosion pits is the critical factor that affects the dangerous area and stress concentration factor. The development of secondary pits will lead to the multiplier effect of stress concentration factor. The maximum stress is basically located at the mouth or middle part of secondary pits. In addition, the pit angle does not change the distribution of dangerous area, but with the pits angle increasing, the stress concentration factor increases as a whole. The contours that classical butterfly-like distribution rotates and the rotation angle is basically the same with that of the corrosion pits. Furthermore, with the pits spacing increasing, the stress concentration factor increases gradually and converges to the fixed value, which is equal to the stress concentration factor under the single pit. Finally, the relationship between the pits parameters and stress concentration factor is systematically predicted.

To Study the Effect of Stress Concentration Factor on Mild Steel Due to Heat Treatment

To Study the Effect of Stress Concentration Factor on Mild Steel Due to Heat Treatment

Effect of nonlinear material behavior of laminated composite plates with central rectangular hole subjected to out -of- plane loading

The purpose of this paper is to investigate the effect of nonlinear material behavior on four layered, symmetric; angle-ply laminated composite plate with various fiber-orientation angles; ( θ = 30°, 45° and 60°). The plate has a central square-hole and subjected to out-of-plane uniformly distributed load. The effect of Stress Concentration Factor (SCF) resulting from redistribution of in-plane stresses ( σ x , σ y , τ xy ) around the hole was taken into consideration. Square plates with simply supported boundary conditions were considered in the present study. The analysis was carried out utilizing the ANSYS-computer program. The presence of a central hole was found to concentrate the maximum stresses at the corners of the hole. The nonlinear material behavior was found to redistribute the in-plane stresses more reasonably and smoothly around the hole-perimeter and hence resulting in smaller SCF-values.

Some Influencing Variables on Internal Fatigue Crack Initiation in Structural Materials

Major variables which cause internal fatigue crack initiation are nonmetallic inclusions in high strength steels, surface roughness and notch in structural components and corrosive environments. This paper focused on the effect of stress concentration factor and corrosive environment for internal fatigue crack initiation of structural materials mainly based upon author's experimental results.In the results of conventional and ultrasonic fatigue testing on notched specimens with stress concentration factor of 1.5, 2.0 and 2.5 for 0.65 mass % carbon matrix high speed steel with HRC 60.7, subsurface fatigue crack initiation was observed on all notched specimens at failed number of cycles over than 106. On the contrary fatigue crack initiated from notched specimen surface for powdered high speed steel with HRC 67 with stress concentration factor of 2.0. The fatigue crack initiation mode in notched specimens at high cycle region may be governed by surface hardness of high speed steels.The different effect of corrosive environment on fatigue crack initiation is demonstrated in the plate bending fatigue testing results of 1% carbon steel and13Cr-1Mo steel in refrigeration compressor gaseous environment. For 1% carbon steel fatigue crack initiated from subsurface at lower fatigue life of 5x106 cycles,while fatigue crack initiated from surface corrosion pit at higher fatigue life of 5x106 cycles. For 13Cr-1Mo steel subsurface fatigue crack initiation was predominantly observed in air and in refrigeration compressor gaseous environment.

Ultrasonic fatigue testing on high strength steel: Effect of stress concentration factors associated with corrosion pitting holes

Ultrasonic fatigue tests at the frequency of 20 kHz were carried out on the hot rolled low alloy steel grade (known as R5), which according to the International Classification Society of offshore systems, it is a steel with the highest ultimate tensile strength to manufacture mooring chains and accessories intended to position mooring applications. Tests were carried out at constant load ratio R = −1 on pre-corroded and no-corroded hourglass shape specimens; pre-corrosion was implemented according to ASTM standard G85. Stress concentration between two and three close hemispherical pitting holes on hourglass shape specimen undergoing uniaxial loading were obtained by finite element method. Experimental results show that fatigue life decreases with the proximity of two close pitting holes on the fracture surface. An exponential law is proposed for the stress concentration factor evolution with the proximity of two close pitting holes of identical radius; the trend of this law is confirmed by experimental results. Finally, fracture surfaces were analyzed and conclusions were listed concerning fatigue life, proximity of pitting holes on fracture surface, and the associated stress concentration factors.

Effect of stress concentration factors on the structural integrity assessment of multi-planar offshore tubular DKT-joints based on the fracture mechanics fatigue reliability approach

A reasonably accurate estimate of fatigue reliability is considered to be essential for offshore structures due to their high construction cost and failure consequences. In the present paper, firstly, a fracture mechanics based fatigue limit-state function is derived and effects of assigning different values to deterministic variables involved in this limit-state function on the results of reliability analysis are investigated. These deterministic variables are the material parameter, number of stress cycles, and the mean value of critical crack size. Afterwards, effects of stress concentration factors (SCFs) on the reliability of the tubular joint are studied. The SCF is one of the most important parameters in the fatigue reliability analysis, which exhibits considerable scatter. Results showed that change of the mean value of SCF, from the value typically assumed in the previous research works (=2.5) to a realistic value obtained in the present research for a widely used multi-planar joint (∼15), leads to considerable decrease in the reliability index and consequently significant increase in the probability of failure. However, change of the coefficient of variation (CoV) of SCFs, from the typically assumed value (=0.15) to a realistic value obtained in the present research (∼1.048), does not considerably affect the results.

Fatigue Behavior of the Low-Strength Steel Welded Joints Treated by TIG Dressing and Ultrasonic Peening Combined Method

Butt-joint specimens of Q235B low-strength steel were treated by TIG dressing and ultrasonic peening combined method. The paper presents comparative fatigue test for welded specimens in the as-welded condition and specimens treated by TIG dressing, ultrasonic peening treatment (UPT) and the combined method. When the ratio of stress R=0.1, contrasted with the specimens in as welded condition, the fatigue strength of the specimens treated by TIG dressing is increased by 36%. The fatigue strength of the specimens treated by the combined method and UPT are almost the same, which are increased by 57% and 56% respectively. In the high stress level, weld toe treated by the combined method has smaller stress concentration factor than that of UPT, resulting in less release of residual compressive stress. So it's more effective to improve the fatigue life by the combined method. While in the low stress level, the residual compressive stress of weld toe treated by the combined method and UPT are nearly the same. Besides, the effect of stress concentration factor is smaller, thus the fatigue life of the two methods have little difference.

Environmentally assisted cracking of 18%Ni maraging steel

Slow strain rate testing of notched cylindrical specimens of 18Ni2400 maraging steel has been carried out in air with 30% relative humidity and synthetic seawater environments. Peak-aged condition has been chosen, considering the relevance to engineering applications. Studies have also been carried out with different notch geometries to understand the effect of stress concentration factor. It is concluded from the study that (i) degree of stress concentration at the notch influences the notched tensile strength (ii) mild hydrogen embrittlement seems to occur in air environment, (iii) synthetic seawater environment drastically brings down the notched tensile strength and time to fracture (iv) environmentally assisted cracking occurs in air tests in quasicleavage and microvoid coalescence modes and in seawater tests in intercrystalline mode.

Fatigue Properties of Austenitic Stainless Steel with Circumferential Notch

The effect of stress concentration factor on the fatigue properties of typical austenitic stainless steel SUS304 have been investigated using the circumferentially notched specimens. The notch of specimens has six kinds of radii, i.e. ρ = ∞ (i.e. plain specimen), 2.0, 1.0, 0.6, 0.3, and 0.1 mm with constant notch depth (t=0.2mm). Though the fatigue cracks in the specimens with a blunt notch initiate at one point, those in the specimens with a sharp notch initiate at several points. There exist the slip bands in the surface of the specimen under the stress amplitude of fatigue limit by 1×107 cycles, and do not exist the non-propagating micro-cracks in all kinds of the specimens. Furthermore, it has been found that notch sensitivity of austenitic stainless steels is higher than that of a typical plain carbon steels under the higher stress concentration factor region.

応力集中係数と溶接残留応力の効果 高強度鋼溶接継手の疲労強度とその支配因子

The fatigue strength of mild and high strength steel plates and their welded joints is studied with respect to stress concentration factor (Kt) and welding residual stress. The fatigue strength of high strength steel is higher than that of mild steel when Kt is less than 3, though the effect of strength on fatigue strength becomes smaller as Kt increases. The fatigue strength of welded joint of high strength steel, however, is similar to that of mild steel in the case that K2 is 1.68. The tensile residual stress in the welded joints of high strength steels is higher than that of mild steel. The effect of stress concentration factor on fatigue strength and the existence of higher welding residual stress in the higher strength steel welded joint conclude that the welding residual stress has a predominant effect on the fatigue strength of the welded joint of high strength steel.

Calculation of the effect of stress concentration factor with multicycle fatigue

Calculation of the effect of stress concentration factor with multicycle fatigue