Two- and Three-Dimensional Cases of Stress Concentration, and Comparison With Fatigue Tests

1936 ◽  
Vol 3 (1) ◽  
pp. A15-A22 ◽  
Author(s):  
R. E. Peterson ◽  
A. M. Wahl
Keyword(s):  
Fatigue Strength ◽  
Stress Concentration ◽  
Stress Concentration Factor ◽  
Concentration Factor ◽  
Practical Importance ◽  
Three Dimensional ◽  
Fatigue Tests ◽  
Carbon Steels ◽  
Dimensional Case ◽  
Strain Measurements

Abstract This paper reports the results of a study of some two- and three-dimensional cases of stress distribution with particular reference to shafts having fillets or transverse holes, these being of considerable practical importance. To determine the stress-concentration factor kt in such cases, strain measurements were made, using a specially developed extensometer with a gage length of 0.1 in. The results of these strain measurements indicate that for shaft fillets in bending (three-dimensional case) the stress-concentration factor kt is little different from the values obtained photoelastically on flat specimens having the same r/d ratio (a two-dimensional case). A comparison of these values of kt (both for shafts with fillets and with transverse holes), with data from fatigue tests, leads to the following observations: (1) In some cases fatigue results are quite close to theoretical stress-concentration values. (2) Fatigue results for alloy steels and quenched carbon steels are usually closer to theoretical values than are the corresponding fatigue results for carbon steels not quenched. (3) With decrease in size of specimen, the reduction in fatigue strength due to a fillet or hole becomes somewhat less; and for very small fillets or holes the reduction in fatigue strength is comparatively small. (4) Sensitivity factors determined for small specimens should not be applied to the design of machine parts regardless of size.

Pipe Joint Management for Risers and Pipelines

2021 ◽  
Author(s):  
Ghiath (Guy) Mansour
Keyword(s):  
Fatigue Strength ◽  
Stress Concentration ◽  
Software Development ◽  
Wall Thickness ◽  
Stress Concentration Factor ◽  
Concentration Factor ◽  
Joint Management ◽  
Pipe Joints ◽  
Best Fit ◽  
Pipe Joint

Abstract Minimizing the stress concentration factor (SCF) in pipe joint welding subjected to fatigue is a major concern. Machining the joint ends is one way to achieve this. However, this adds cost, time, risk of potential crack starters, and loss of wall thickness which is detrimental for fatigue, strength, and engineering criticality assessment (ECA) in particular. Pipe joint sorting (certain joints in sequence) and end matching (rotating the pipe joints for best fit) are other ways. However, this adds time, costly logistics, risk of errors, and does not guarantee the minimum possible SCF is achieved. In a typical project, more pipe joints are procured than required in order to mitigate contingencies. For pipelines, this overage is typically a percentage of the required number of joints or pipeline length. For risers, typically double the required number of joints is procured where half of the joints is sent offshore for installation and the remaining half is kept onshore for a spare riser. Then, it becomes very important to send for installation the best pipe joints that produce the best (lowest) SCFs out of the entire batch of pipe joints. This requires calculating the SCF for every potential match of any random joints to be welded together, and then choosing the best joints. Performing such calculations by spreadsheet is not feasible considering the tremendous number of required iterations and calculations. A pipe joint management software development is presented herein which accomplishes this task and examples provided to illustrate the benefits. Note: Selecting pipe joints with the best end measurements, whether ID, OD, OOR, or thickness does not guarantee that the minimum possible SCFs will be achieved since the SCF is a function of all those measurements.

Simple formulae for the stress concentration factor for two- and three-dimensional holes in finite domains

2002 ◽  
Vol 37 (3) ◽  
pp. 259-264 ◽  
Author(s):  
Q. Z Wang
Keyword(s):  
Stress Concentration ◽  
Circular Hole ◽  
Stress Concentration Factor ◽  
Concentration Factor ◽  
Spherical Cavity ◽  
Three Dimensional ◽  
Finite Domain ◽  
Three Dimensional Models ◽  
Finite Domains ◽  
Asymptotic Validity

First, based on an approximate analysis, simple closed-form expressions of the stress concentration factor (SCF) for two- or three-dimensional models with a circular hole or a spherical cavity in a finite domain are derived. Then, an asymptotic method is adopted to improve the accuracy of the derived solutions for an extremely large circular hole or spherical cavity, when the remaining ligament approaches zero. Exact limit SCF values for these two kinds of models were given by Koiter; these values are used for the adjustment of the coefficients in the SCF expressions. Finally, simple SCF formulae for these finite domain problems are obtained, their accuracy is demonstrated to be very good by comparison with the available data from the literature, and the asymptotic validity is guaranteed.

Numerical Investigation of Stress Concentration Factor at Irregular Corrosion Pit Under Tension-Torsion Loading

2014 ◽  
Author(s):  
Yuhui Huang ◽  
Chengcheng Wang ◽  
Shan-Tung Tu ◽  
Fu-Zhen Xuan ◽  
Takamoto Itoh
Keyword(s):  
Finite Element Analysis ◽  
Finite Element ◽  
Stress Concentration ◽  
Aspect Ratio ◽  
Stress Concentration Factor ◽  
Concentration Factor ◽  
Three Dimensional ◽  
Element Analysis ◽  
Stress Concentration Factors ◽  
Local Dissolution

Finite element analysis is adopted to study the stress concentration of pit area under tension-torsion loading. The stress concentration factors under regular evolution and irregular evolution of pits are investigated by conducting a series of three-dimensional semi-elliptical pitted models. Based on the finite element analysis, it can be concluded that pit aspect ratio (a/2c) is a significant parameter affecting stress concentration factor (SCF) for regular evolution pits. Pits, having higher aspect ratio, are very dangerous form and can cause significant reduction in the load carrying capacity. When local dissolution occurs in the pitting area, SCF will have a sharp increase, it is more probable for a crack to initiate from these areas compared with pits for regular evolution. Furthermore, local dissolution coefficient is proposed to study effect of local dissolution within the pit on SCF.

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

2011 ◽  
Vol 295-297 ◽  
pp. 1885-1889
Author(s):  
Sen Li ◽  
Dong Po Wang ◽  
Hai Zhang ◽  
Bo Tan
Keyword(s):  
Fatigue Life ◽  
Fatigue Strength ◽  
Stress Concentration ◽  
Compressive Stress ◽  
Stress Level ◽  
Stress Concentration Factor ◽  
Concentration Factor ◽  
Combined Method ◽  
Ultrasonic Peening ◽  
Weld Toe

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.

Three-Dimensional Elastic Stress Fields of Finite Thickness Plates with Elliptical Hole

2007 ◽  
Vol 353-358 ◽  
pp. 74-77
Author(s):  
Zheng Yang ◽  
Chong Du Cho ◽  
Ting Ya Su ◽  
Chang Boo Kim ◽  
Hyeon Gyu Beom
Keyword(s):  
Stress Concentration ◽  
Plane Strain ◽  
Plane Stress ◽  
Stress Concentration Factor ◽  
Concentration Factor ◽  
Maximum Stress ◽  
Elastic Stress ◽  
Finite Thickness ◽  
Plate Thickness ◽  
Three Dimensional

Based on detailed three-dimensional finite element analyses, elastic stress and strain field of ellipse major axis end in plates with different thickness and ellipse configurations subjected to uniaxial tension have been investigated. The plate thickness and ellipse configuration have obvious effects on the stress concentration factor, which is higher in finite thickness plates than in plane stress and plane strain cases. The out-of-plane stress constraint factor tends the maximum on the mid-plane and approaches to zero on the free plane. Stress concentration factors distribute ununiformly through the plate thickness, the value and location of maximum stress concentration factor depend on the plate thickness and the ellipse configurations. Both stress concentration factor in the middle plane and the maximum stress concentration factor are greater than that under plane stress or plane strain states, so it is unsafe to suppose a tensioned plate with finite thickness as one undergone plane stress or plane strain. For the sharper notch, the influence of three-dimensional stress state on the SCF must be considered.

Effects of Perforation on the Collapsing Strength of Casing

2013 ◽  
Vol 395-396 ◽  
pp. 881-886
Author(s):  
Yu Guang Cao ◽  
Shi Hua Zhang ◽  
Xin Ren
Keyword(s):  
Stress Concentration ◽  
Flat Plate ◽  
Elasticity Theory ◽  
Stress Concentration Factor ◽  
Mechanical Model ◽  
Concentration Factor ◽  
Three Dimensional ◽  
Theoretical Equation ◽  
Fem Model ◽  
Strength Factor

In this study, three-dimensional mechanical model of the perforated casing was simplified as flat plate mechanical model. The theoretical equation for the calculation of collapsing strength factor for a perforated casing under squeeze was derived as per elasticity theory. Three-dimensional FEM model of a perforated casing was built using ANSYS and analysis was performed. The stress concentration factor (SCF) was discussed for perforated casing in this paper and the effects of aperture on SCFs were analyzed in detail.

Fatigue Life Properties of Circumferentially-Notched Bar of Austenitic Stainless Steel With Various Concentration Factors

2018 ◽  
Author(s):  
Naoaki Nagaishi ◽  
Michio Yoshikawa ◽  
Saburo Okazaki ◽  
Hisao Matsunaga ◽  
Junichiro Yamabe ◽  
...  
Keyword(s):  
Stainless Steel ◽  
Fatigue Life ◽  
Stress Concentration ◽  
Austenitic Stainless Steel ◽  
Stress Concentration Factor ◽  
Concentration Factor ◽  
Stress Ratio ◽  
Ambient Air ◽  
Fatigue Tests ◽  
Concentration Factors

Fatigue tests were performed using three types of round-bar specimens of Type 304, meta-stable, austenitic stainless steel. The specimens had circumferential notch with stress concentration factors, Kt, of 2, 3 or 6.6. Load controlled fatigue tests were conducted at stress ratio, R, of 0.1 and −1 in ambient air at room temperature. At R of 0.1, fatigue life was decreased with an increase in the stress concentration factor. Conversely, at R of −1, the stress concentration factor had little influence on the fatigue life. To understand the mechanism of the stress ratio effect, local deformation behavior at and beneath the notch root during the fatigue test was computed by means of finite element analysis considering that the plastic constitutive model describes the cyclic stress-strain response.

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