Criteria of Mora-Coulomb with Three Parameters of Material

A modified Mohr – Coulomb criterion is presented. This criterion, in addition to adhesion and the angle of internal friction, contains the third parameter of the material (d). Depending on the value of this parameter (d), the modified criterion can take the form of the original Mohr – Coulomb criterion (with d = 0.5) or the original Treska criterion (with d = 0). For all other values of the parameter (d), varying in the range of 0 <d <0.5, the tangential stresses by the modified criterion are larger than the Mohr – Coulomb criterion, but less than the Tresca criterion. The paper presents the methodology and results of determining this parameter (d) using experiments on the triaxial compression of soils. The technique contains recommendations for the appointment the value of the axial strain of the sample material when determining the value of the parameter d. The value of the ultimate deformation is advisable to take in the range from 8 to 12%. This range is due to the fact that with axial deformation of the sample of 8%, the formation of slip areas begins in it, and with axial deformation of the sample 12%, the slip area is completely formed. In this case, the parameter d varies in the range 0 <d <0.5, having a shear strength bigger than in the Tresca criterion, but less than in the original Mohr – Coulomb criterion. The tangential stresses according to the modified criterion, on the contrary, have a bigger value than according to the Mohr – Coulomb criterion, but the values of the tangential stresses are lower than in the Tresca criterion.

Creep Response of Rotating Composite Discs having Exponential Hyperbolic Linear and Constant Thickness Profiles

The study compares the steady state creep response of rotating Al-SiC discs having constant, linear, hyperbolic and exponential thickness with different thickness profiles. All the discs are assumed to have equal volume with the same average thickness. The creep behaviour of the disc material is described by threshold stress based law while the yielding is assumed to follow Tresca criterion. The variable thickness disc is observed to have superior creep response, expressed in terms of stresses and strain rates, to a constant thickness disc. Amongst variable thickness discs, the creep response is observed to be superior for linear thickness disc, when the inner thickness of all the discs is kept the same. However, for the same outer thickness, the disc having hyperbolic thickness profile exhibits the best creep response.

Elastoplastic Analysis of Two-Layered Circular Lining Based on the Unified Strength Theory

Based on the Unified Strength Theory (UST), elastoplastic analysis of the two-layered circular lining is carried out. The stresses, displacements, and the elastic and plastic zones in both layers are discussed under different values of Young’s moduli of the inner and outer layers. The results reveal that, compared to the single-layered lining, the tangential stress distributions in the two-layered linings are more reasonable along the radial direction, which is beneficial to enhance the overall elastic and plastic ultimate bearing capacities. When considering the intermediate stress (i.e., the axial load), the elastic ultimate bearing capacity will be higher. However, the plastic ultimate bearing capacity remains unchanged. Moreover, a comparison between the Unified Strength Theory and Tresca Criterion is analyzed as well.

Evaluation of Burst Pressure of Corroded Pipe Segments Using Three-Dimensional Finite Element Analyses

In this paper, three-dimensional finite element models are developed to simulate full-scale burst tests of corroded pipes containing multiple naturally occurring corrosion anomalies. Both the von Mises and Tresca yield criteria and associated flow rules are employed in finite element analysis (FEA). For the Tresca criterion, the corresponding constitutive model subroutine is developed and incorporated in the FEA. The accuracy of FEA is investigated by comparing the burst pressures observed in the tests and corresponding burst pressures predicted using FEA. The implications of using the von Mises and Tresca criteria for the accuracy of the predicted burst pressure are investigated. Sensitivity analyses are also carried out to investigate the impact on the predicted burst pressure due to the mesh density in the corroded region, characterization of the geometry of the corrosion cluster and different types of element (e.g. solid and shell elements) used in FEA. The results suggest that the Tresca criterion always underestimates the burst pressure and the von Mises yield criterion predicts the burst pressure accurately. This study demonstrates the feasibility of using high-fidelity FEA and the Tresca yield criterion to simulate full-scale burst tests of corroded pipes and therefore establish a large database of burst pressure capacities of corroded pipes that can be used to develop an accurate, practical burst pressure capacity model amenable to the pipeline integrity management practice.

Effect of Yield Criterion on Stress Distribution and Maximum Safe Pressure for an Autofrettaged Gun Barrel

<p>World artillery in the present scenario is changing its role from defensive to aggressive nature and is attempting to achieve higher penetration into enemy targets. Even for an autofrettaged gun barrel, higher ranges requirement leads to higher barrel weight and its associated demerits. The design of gun barrel is based on the choice of yield criteria. Tresca yield criterion provides conservative design for a ductile barrel material. On the other hand, more accurate von Mises criterion presents complexity. The two criteria to evaluate various parameters required for design of an autofrettaged gun barrel are compared. The methodology for evaluation of maximum safe pressure, based on von Mises criterion, for an autofrettaged gun barrel is also included in the paper. Based on case study included in the article, for an autofrettaged gun barrel or pressure vessel with uniform thickness, a theoretical weight reduction of approximately 16 per cent is feasible with von Mises criterion as compared to Tresca criterion.</p>

Prediction of Burst Pressure of Pipes With Geometric Eccentricity

An analytical model was proposed in this paper to predict the burst pressure of a pipe with geometric eccentricity. With application of the complex elastic potential function method in a bipolar coordinate system, the authors first derived an analytical solution of stresses in an eccentric pipe and then obtained the formula of predicting burst pressure by combining the solution with the Tresca criterion. Finally, the effect of eccentricity and the ratio of thickness to diameter of pipe on burst pressure were discussed. Our results show that a slight eccentricity can significantly decrease the burst pressure. In the special case of zero-eccentricity for a concentric pipe, our model yields results that are consistent with experiments data published by others and theoretical results predicted by models proposed by other researchers without considering the effect of eccentricity. In the case of eccentricity for an eccentric pipe, the calculating results of our model are also consistent with that of finite element model (FEM). The theoretical model and results presented in this paper have a broader application in predicting the burst pressure for pipes commonly used in oil and gas industry.

Numerical Investigation of the Undrained Compression and Pull-Out Capacity of Suction Foundations in Clay

This paper presents the results of three-dimensional finite difference analysis of suction foundations in uniform and non-uniform clays under undrained conditions. The Tresca criterion was used to simulate the stress-strain response. The bearing capacity of the foundations was investigated, with the degree of nonhomogeneity (kD/sum) of soil varying from 0 to 5, and the embedment depth being up to four times the foundation diameter. The end bearing capacity factor in compression and the reverse bearing capacity factor in tension were both calculated and were compared with each other under different foundation displacements. Numerical results showed that the ultimate bearing capacity factor can have the same value in cases of both compression and tension. The recommended ultimate bearing capacity factor is determined on the basis of the embedment ratio and displacement magnitude, and the displacement is not more than 30% of the foundation diameter. Finally, two equations are proposed to evaluate both the bearing capacity factor and the effective depth factor.