Pressure Pipe Damage: Numerical Estimation of Point Load Effect II

2013 ◽  
Vol 577-578 ◽  
pp. 533-536 ◽  
Author(s):  
Zdeněk Majer ◽  
Michal Zouhar ◽  
Martin Ševčík ◽  
Luboš Náhlík ◽  
Pavel Hutař
Keyword(s):  
Stress Intensity Factor ◽  
Stress Intensity ◽  
Intensity Factor ◽  
Hoop Stress ◽  
Simple Relation ◽  
Point Load ◽  
Numerical Estimation ◽  
Load Effect ◽  
Pressure Pipe ◽  
External Point

It has been shown that the service lifetime of buried pipes can be reduced especially in relation to stress concentration caused by external point loads. If the pipe is loaded locally the stress is concentrated there and a crack can initiate at this position or the existing crack can be affected by corresponding stress redistribution. In the paper, the effect of a hard indenter, material properties, and the hoop stress level on the stress intensity factor of the axial inner crack are evaluated. A simple relation for estimation of the stress intensity factor value without FEM simulations is proposed.

Pressure Pipe Damage: Numerical Estimation of Point Load Effect

2012 ◽  
Vol 525-526 ◽  
pp. 177-180 ◽  
Author(s):  
Michal Zouhar ◽  
Pavel Hutař ◽  
Martin Ševčík ◽  
Luboš Náhlík
Keyword(s):  
Hoop Stress ◽  
Point Load ◽  
Simple Relationship ◽  
Numerical Estimation ◽  
Load Effect ◽  
Pipe Wall Thickness ◽  
Pressure Pipe ◽  
Service Lifetime ◽  
External Point ◽  
Pipeline Design

The most relevant loading conditions for real polymer pipe systems are not only internal pressure, but also loading caused by sand embedding including bending or different kinds of point loads. It has been shown that service lifetime of buried pipes can be reduced especially due to stress concentration caused by external point loads. If the pipe is loaded locally the stress is concentrated here and a crack can initiate at this position or the existing crack can be affected by corresponding stress redistribution. In the paper the effect of the hard indenter, Poissons ratio, hoop stress level and pipe wall thickness on the crack shape was estimated using numerical simulations of the creep crack propagation based on finite element method. Relation between crack length and crack width was found and expressed by simple relationship. A deeper understanding of the point load effect in order to prevent unexpected failure of the pipelines is of paramount importance for pipeline design.

The Numerical Analysis and Experimental Study of the Stress Intensity Factor and Outer Surface Strain of the Pressure Pipe with Internal Longitudinal-Cracks

2016 ◽  
Vol 853 ◽  
pp. 221-225
Author(s):  
Jia Sheng He ◽  
Meng Qi Yan ◽  
Xiao Ming Zhu
Keyword(s):  
Stress Intensity Factor ◽  
Stress Intensity ◽  
Intensity Factor ◽  
Outer Surface ◽  
Crack Size ◽  
Surface Strain ◽  
Strain Variation ◽  
Pressure Pipe ◽  
Longitudinal Cracks ◽  
Relationship Of

The strain characteristics in the outer surface of the pipe and the stress intensity factor in crack front with internal longitudinal-cracks were analyzed by the finite element method. According to the results of analysis, the outer surface strain variation to crack size was got and the relationship of stress intensity factor and crack size was known. Based on resistance strain gauges and fiber optic sensing technology, pressure pipe crack extension monitoring device was designed and the outer surface circumferential strain were tested .The results of finite element analysis and experiment are in good agreement. The outer surface strain variation in this paper can be used to analyze the situation of internal longitudinal-cracks extension.That relationship of stress intensity factor and crack size has an important reference to the safety assessment of pipe with internal longitudinal-crack.

scholarly journals Transient Analysis for Antiplane Crack Subjected to Dynamic Loadings

1991 ◽  
Vol 58 (3) ◽  
pp. 703-709 ◽  
Author(s):  
Chien-Ching Ma ◽  
Ying-Chung Hou
Keyword(s):  
Stress Intensity Factor ◽  
Stress Intensity ◽  
Intensity Factor ◽  
Shear Wave ◽  
Dynamic Stress Intensity Factor ◽  
Crack Tip ◽  
Point Load ◽  
Crack Face ◽  
Kinked Crack ◽  
Kink Angle

The problem considered here is the antiplane response of an elastic solid containing a half-plane crack subjected to suddenly applied concentrated point forces acting at a finite distance from the crack tip. A fundamental solution for the dynamic dislocation is obtained to construct the dynamic fracture problem containing a characteristic length. Attention is focused on the time-dependent full-field solutions of stresses and stress intensity factor. It is found that at the instant that the first shear wave reaches the crack tip, the stress intensity factor jumps from zero to the appropriate static value. The stresses will take on the appropriate static value instantaneously upon arrival of the shear wave diffracted from the crack tip, and this static value is thereafter maintained. The dynamic stress intensity factor of a kinked crack from this stationary semi-infinite crack after the arrival of shear wave is obtained in an explicit form as a function of the kinked crack velocity, the kink angle, and time. A perturbation method, using the kink angle as the perturbation parameter, is used. If the maximum energy release rate is accepted as the crack propagation criterion, then the crack will propagate straight ahead of the original crack when applying point load at the crack face.

Damage accumulation near a hole under low cycle fatigue proceeding from measurements of local deformation response

2020 ◽  
Vol 86 (10) ◽  
pp. 46-55
Author(s):  
S. I. Eleonsky ◽  
Yu. G. Matvienko ◽  
V. S. Pisarev ◽  
A. V. Chernov
Keyword(s):  
Stress Intensity Factor ◽  
Stress Intensity ◽  
Intensity Factor ◽  
Damage Accumulation ◽  
Stress Ratio ◽  
Low Cycle Fatigue ◽  
Accumulation Process ◽  
Stress Range ◽  
Cycle Fatigue ◽  
Deformation Response

A new destructive method for quantitative determination of the damage accumulation in the vicinity of a stress concentrator has been proposed and verified. Increase of damage degree in local area with a high level of the strain gradient was achieved through preliminary low-cycle pull-push loading of plane specimens with central open holes. The above procedure is performed for three programs at the same stress range (333.3 MPa) and different stress ratio values 0.33, – 0.66 and – 1.0, and vice versa for two programs at the same stress ratio – 0.33 and different stress range 333.3 and 233.3 MPa. This process offers a set of the objects to be considered with different degree of accumulated fatigue damages. The key point of the developed approach consists in the fact that plane specimens with open holes are tested under real operation conditions without a preliminary notching of the specimen initiating the fatigue crack growth. The measured parameters necessary for a quantitative description of the damage accumulation process were obtained by removing the local volume of the material in the form of a sequence of narrow notches at a constant level of external tensile stress. External load can be considered an amplifier enhancing a useful signal responsible for revealing the material damage. The notch is intended for assessing the level of fatigue damage, just as probe holes are used to release residual stress energy in the hole drilling method. Measurements of the deformation response caused by local removing of the material are carried out by electronic speckle-pattern interferometry at different stages of low-cycle fatigue. The transition from measured in-plane displacements to the values of the stress intensity factor (SIF) and the T-stress was carried out on the basis of the relations of linear fracture mechanics. It was shown that the normalized dependences of the stress intensity factor on the durability percentage for the first notch (constructed for four programs of cyclic loading with different parameters), reflect the effect of the stress ratio and stress range of the loading cycle on the rate of damage accumulation. The data were used to obtain the explicit form of the damage accumulation function that quantitatively describes damage accumulation process. The functions were constructed for different stress ratios and stress ranges.

A new type of cracks adding to Griffith–Irwin cracks

2019 ◽  
Vol 485 (2) ◽  
pp. 162-165
Author(s):  
V. A. Babeshko ◽  
O. M. Babeshko ◽  
O. V. Evdokimova
Keyword(s):  
Stress Intensity Factor ◽  
Stress Intensity ◽  
Intensity Factor ◽  
Crack Tip ◽  
Stress Concentrations ◽  
New Type

The distinctions in the description of the conditions of cracking of materials are revealed. For Griffith–Irwin cracks, fracture is determined by the magnitude of the stress-intensity factor at the crack tip; in the case of the new type of cracks, fracture occurs due to an increase in the stress concentrations up to singular concentrations.

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