On New Modifications of Some Strength Criteria for Anisotropic Materials

2016 ◽  
Vol 724 ◽  
pp. 53-57 ◽  
Author(s):  
S.L. Shambina ◽  
F.V. Rekach ◽  
Y.V. Belousov
Keyword(s):  
Limit State ◽  
Strength Criterion ◽  
Material Strength ◽  
Small Element ◽  
Exact Results ◽  
Strength Condition ◽  
Stress Space ◽  
Strength Criteria ◽  
State Of Stress ◽  
The Moment

The strength criterion is the strength condition for a small element of the construction’s material. Strength criterion is analytical interpretation in stress space the allowable boundaries of stress state, within these boundaries the material can work under these conditions without breaking. Since analytical interpretation of the experimental data may be performed in different ways, therefore many different strength criteria exist. Properly chosen strength criterion allows determining the moment when the material is destroyed while it is working under various tense conditions. Also it gives an opportunity to assess the limit state of stress in the most loaded points of the structure. This paper suggests new modifications of some well-known strength criteria which are more comfortable for practical use and can help to achieve more exact results.

A Research on Strength Criteria Based on Material Structure

2014 ◽  
Vol 518 ◽  
pp. 236-243
Author(s):  
Zhen Hai Wei ◽  
Meng Shu Wang ◽  
Ding Li Zhang
Keyword(s):  
Random Distribution ◽  
Strength Criterion ◽  
Tensile Failure ◽  
Material Strength ◽  
Material Structure ◽  
Friction Materials ◽  
Strength Criteria ◽  
Complex Material ◽  
Material Theory ◽  
Strength Models

Strength criteria for materials in the classical elastoplastic theory are formed mostly based on experiments and some assumptions [1, . However, no concensus has been achieved though many strength models were put forward to explore the applicable material strength criteria previously. Even the influence of material structures on strength has not been realized. In this article, the tensile failure strength criterion, shear strength criterion and strength criterion of friction materials are explored on the basis of the model of material with a structure of uniformly random distribution. Through analysis, it can be discovered that the strength criteria in the classical elastoplastic theory can be derived from the complex material theory based on the concept of material structure. However, as the theoretical basis, conditions of derivation and assumptions of concepts are totally different, it is proved that the complex material theory used for studying the material structures can fully cover the contents and conclusions obtained in classical elastoplastic theory.

Material Strength: A Rational Nonequilibrium Energy Model for Complex Loadings

2020 ◽  
Vol 88 (2) ◽  
Author(s):  
Biao Wang
Keyword(s):  
Failure Process ◽  
Strength Criterion ◽  
Energy Model ◽  
Natural Phenomenon ◽  
Material Strength ◽  
Strength Theory ◽  
Reliable Prediction ◽  
Strength Criteria ◽  
Safety Considerations ◽  
Nonequilibrium Energy

Abstract The failure of materials with some sort of loading is a well-known natural phenomenon, and the reliable prediction of the failure of materials is the most important issue for many different kinds of engineering materials based on safety considerations. Classical strength theories with complex loadings are based on some sort of postulations or assumptions, and they are intrinsically empirical criteria. Due to their simplicity, classical strength theories are still widely used in engineering, and they are very easy to incorporate into any finite element code. Recently, a new methodology was proposed by the author. Instead of establishing empirical models, the material failure process was modeled as a nonequilibrium process. Then, the strength criterion was established with the rational stability analysis for the failure process. In this study, the author tried to use this idea to develop a rational thermodynamic strength theory and to make the theory easy to use in engineering, similar to the classical strength criteria. It was found that the predictions of the rational energy strength theory were very reasonable compared to the experimental data even if no postulation was taken. Through the analysis, it seemed that the strength problem could be efficiently tackled using the rational nonequilibrium energy model instead of using some sort of empirical assumptions or models.

Influence of Human Error on Structural Reliability

2017 ◽  
Author(s):  
Eric Brehm ◽  
Robert Hertle ◽  
Markus Wetzel
Keyword(s):  
Human Error ◽  
Structural Reliability ◽  
Failure Modes ◽  
Structural Model ◽  
Limit State ◽  
Design Procedure ◽  
Material Strength ◽  
Limit States ◽  
The Impact

In common structural design, random variables, such as material strength or loads, are represented by fixed numbers defined in design codes. This is also referred to as deterministic design. Addressing the random character of these variables directly, the probabilistic design procedure allows the determination of the probability of exceeding a defined limit state. This probability is referred to as failure probability. From there, the structural reliability, representing the survival probability, can be determined. Structural reliability thus is a property of a structure or structural member, depending on the relevant limit states, failure modes and basic variables. This is the basis for the determination of partial safety factors which are, for sake of a simpler design, applied within deterministic design procedures. In addition to the basic variables in terms of material and loads, further basic variables representing the structural model have to be considered. These depend strongly on the experience of the design engineer and the level of detailing of the model. However, in the clear majority of cases [1] failure does not occur due to unexpectedly high or low values of loads or material strength. The most common reasons for failure are human errors in design and execution. This paper will provide practical examples of original designs affected by human error and will assess the impact on structural reliability.

Effect of Lu¨ders Bands on the Bending Capacity of Steel Tubes

2010 ◽  
Author(s):  
Julian F. Hallai ◽  
Stelios Kyriakides
Keyword(s):  
Limit State ◽  
Solution Procedure ◽  
Inhomogeneous Deformation ◽  
Pure Bending ◽  
Steel Tubes ◽  
Deformation Regime ◽  
Bending Capacity ◽  
The Moment ◽  
T Values ◽  
Structural Instabilities

In several offshore applications hot-finished pipe that often exhibits Lu¨ders bands is bent to strains of 2–3%. Lu¨ders banding is a material instability that leads to inhomogeneous plastic deformation in the range of 1–4%. It can precipitate structural instabilities and collapse of the pipe. Experiments and analysis are used to study the interaction of the prevalent structural instabilities under bending with Lu¨ders banding, with the objective of providing guidance to the designer. Pure bending experiments on tubes of various D/t values reveal that Lu¨ders bands result in the development of inhomogeneous deformation in the structure, in the form of coexistence of two curvature regimes. Under rotation controlled bending, the higher curvature zone(s) gradually spreads while the moment remains essentially unchanged. For relatively low D/t tubes with relatively smaller Lu¨ders strain, the whole tube eventually is deformed to the higher curvature, subsequently entering the usual hardening regime where it continues to deform uniformly until the expected limit state is reached. For higher D/t tubes and/or for materials with longer Lu¨ders strain, the structure collapses during the inhomogeneous deformation regime. This class of problems is analyzed using 3D finite elements and an elastic-plastic constitutive model with an up-down-up material response. It will be demonstrated that the solution procedure followed can simulate the experiments with consistency.

Markovian Analysis of Aging Distributed Systems Remaining Life

2014 ◽  
Author(s):  
Anna Bushinskaya ◽  
Sviatoslav Timashev
Keyword(s):  
Distributed Systems ◽  
Markov Process ◽  
Residual Life ◽  
Limit State ◽  
Real Life ◽  
Random Variable ◽  
Operating Pressure ◽  
Remaining Life ◽  
Failure Pressure ◽  
The Moment

Correct assessment of the remaining life of distributed systems such as pipeline systems (PS) with defects plays a crucial role in solving the problem of their integrity. Authors propose a methodology which allows estimating the random residual time (remaining life) of transition of a PS from its current state to a critical or limit state, based on available information on the sizes of the set of growing defects found during an in line inspection (ILI), followed by verification or direct assessment. PS with many actively growing defects is a physical distributed system, which transits from one physical state to another. This transition finally leads to failure of its components, each component being a defect. Such process can be described by a Markov process. The degradation of the PS (measured as monotonous deterioration of its failure pressure Pf (t)) is considered as a non-homogeneous pure death Markov process (NPDMP) of the continuous time and discrete states type. Failure pressure is calculated using one of the internationally recognized pipeline design codes: B13G, B31Gmod, DNV, Battelle and Shell-92. The NPDMP is described by a system of non-homogeneous differential equations, which allows calculating the probability of defects failure pressure being in each of its possible states. On the basis of these probabilities the gamma-percent residual life of defects is calculated. In other words, the moment of time tγ is calculated, which is a random variable, when the failure pressure of pipeline defect Pf (tγ) > Pop, with probability γ, where Pop is the operating pressure. The developed methodology was successfully applied to a real life case, which is presented and discussed.

scholarly journals Strength criterion for a plane stress reinforced concrete element under a special action

Vestnik MGSU ◽  
2020 ◽  
pp. 1513-1522
Author(s):  
Natalia V. Fedorova ◽  
Vu Ngoc Tuyen ◽  
Igor A. Yakovenko
Keyword(s):  
Reinforced Concrete ◽  
Progressive Collapse ◽  
Concrete Strength ◽  
Limit State ◽  
Strength Criterion ◽  
Structural Systems ◽  
Variable Loading ◽  
Concrete Element ◽  
Theory Of Plasticity ◽  
Concrete Elements

Introduction. Problem solving focused on the protection of buildings and structures from progressive collapse and minimization of resources, needed for this purpose, is becoming increasingly important. In many countries, including Russia, this type of protection is incorporated into national regulatory documents, and, therefore, any research, aimed at developing effective ways to protect structural systems from progressive collapse under special actions, is particularly relevant. In this regard, the present article aims to formulate effective strength criteria for such anisotropic materials as reinforced concrete to analyze plane stressed reinforced concrete structures exposed to sudden structural transformations caused by the removal of one of bearing elements. Materials and methods. To solve this problem, a variant of the generalized theory of plasticity of concrete and reinforced concrete, developed by G.A. Geniev, is proposed for application to the case of variable loading of a plane stressed reinforced concrete element. The acceptability of generalization of the strength criterion, pursuant to the theory of plasticity of concrete and reinforced concrete under static loading, and the applicability of this criterion to variable static-dynamic loading of reinforced concrete are used as the main hypothesis. An algorithm of an approximate method is presented as a solution to this problem; it allows to analyze the considered stress-strain state of plane stressed reinforced concrete elements. Results. The numerical analysis of the obtained solution, compared with the results of the experimental studies, was used to evaluate the designed strength criterion for reinforced concrete elements located in the area where the column is connected to the girder of a monolithic reinforced concrete frame in case of a sudden restructuring of a structural system. It is found out that the qualitative nature of the destruction pattern of the area under research, obtained in experiments, corresponds to the destruction pattern, identified by virtue of the analysis performed using the proposed criterion. Conclusions. The variant of the reinforced concrete strength criterion designated for the variable loading of a plane stressed reinforced concrete element and an algorithm for its implementation, based on the theory of plasticity of concrete and reinforced concrete developed by G.A. Geniev, is applicable to the analysis of a special limit state of reinforced concrete elements of structural systems of frames of buildings and structures.

Partial Safety Factors Assessment of Pipes With a Circumferential Surface Flaw

2010 ◽  
Author(s):  
Hideo Machida ◽  
Hiromasa Chitose ◽  
Manabu Arakawa
Keyword(s):  
Fracture Resistance ◽  
Design Method ◽  
Limit State ◽  
Surface Flaw ◽  
Flaw Size ◽  
Material Strength ◽  
State Function ◽  
Safety Factors ◽  
Related Parameter ◽  
Partial Safety Factors

This paper describes the evaluation of partial safety factors (PSF’s) for parameters related to flaw evaluation of pipes which have a circumferential surface flaw, and proposes the important matter which should be pay attention in the setup of the safety factors used in flaw evaluation. PSF’s were evaluated considering randomness of flaw size, a fracture resistance curve (J-R curve) and applied loads using load and resistance factor design method (LRFD). The limit state function is expressed by fracture resistance (resistance-related parameter) and applied J integral (load-related parameter). The measure parameters in the reliability assessment are the flaw size and the J-R curve, and PSF’s of them are larger than those of applied loads. Since the material properties used in the flaw evaluation are generally set to the engineering lower limit of their variation (e.g., 95% lower confidence limit), variation of the flaw size is considered to have important role on flaw evaluation. Therefore, when setting up the safely factors used in Rules on Fitness-for-Service (FFS), it is necessary to take into consideration not only the influence of variation of loads or material strength but the influence of variation of flaw size.

Probabilistic Optimum Design of Composite Laminates

1998 ◽  
Vol 32 (1) ◽  
pp. 68-82 ◽  
Author(s):  
S. Mahadevan ◽  
X. Liu
Keyword(s):  
Objective Function ◽  
Optimum Design ◽  
Composite Laminates ◽  
Plate Theory ◽  
Limit State ◽  
Strength Criterion ◽  
System Level ◽  
State Function ◽  
Practical Procedure ◽  
Reliability Method

This paper proposes a procedure for the optimum design of composite laminates under probabilistic considerations. The problem is formulated to consider the minimization of laminate weight as the objective function and the reliability requirements as the constraints. Both system-level and element-level reliabilities are considered. The first-order reliability method (FORM) is used to estimate the reliability of each ply group, and system reliability is computed based on series or parallel system assumptions. The Tsai-Wu strength criterion is adopted to derive the limit state function of individual ply groups in the laminate. The gradient and sensitivity information of the objective function and the constraints with respect to the design variables are obtained by using sensitivity analysis based on the composite plate theory. Thus the proposed procedure brings together modern concepts of reliability analysis, composite laminate behavior and nonlinear optimization to develop a rational and practical procedure for the optimum design of composite laminates. Numerical examples are presented to demonstrate the effectiveness of the proposed method.

scholarly journals Triaxial Strength Criteria in Mohr Stress Space for Intact Rocks

2020 ◽  
Vol 2020 ◽  
pp. 1-13
Author(s):  
Baohua Guo ◽  
Long Wang ◽  
Yizhe Li ◽  
Yan Chen
Keyword(s):  
Tensile Strength ◽  
Compression Strength ◽  
Triaxial Compression ◽  
Stress Space ◽  
Failure Envelope ◽  
Limit Values ◽  
Strength Criteria ◽  
Triaxial Strength ◽  
Failure Envelopes ◽  
Exponential Equations

Conventional triaxial strength criteria are important for the judgment of rock failure. Linear, parabolic, power, logarithmic, hyperbolic, and exponential equations were, respectively, established to fit the conventional triaxial compression test data for 19 types of rock specimens in the Mohr stress space. Then, a method for fitting the failure envelope to all common tangent points of each two adjacent Mohr’s circles (abbreviated as CTPAC) was proposed in the Mohr stress space. The regression accuracy of the linear equation is not as good as those of the nonlinear equations on the whole, and the regression uniaxial compression strength (σc)r, tensile strength (σt)r, cohesion cr, and internal frictional angle φr predicted by the regression linear failure envelopes with the method for fitting the CTPAC in the Mohr stress space are close to those predicted in the principal stress space. Therefore, the method for fitting CTPAC is feasible to determine the failure envelopes in the Mohr stress space. The logarithmic, hyperbolic, and exponential equations are recommended to obtain the failure envelope in the Mohr stress space when the data of tensile strength (σt)t are or are not included in regression owing to their higher R2, less positive x-intercepts, and more accurate regression cohesion cr. Furthermore, based on the shape and development trend of the nonlinear strength envelope, it is considered that when the normal stress is infinite, the total bearing capacity of rock tends to be a constant after gradual increase with decreasing rates. Thus, the hyperbolic equation and the exponential equation are more suitable to fit triaxial compression strength in a higher maximum confining pressure range because they have limit values. The conclusions can provide references for the selection of the triaxial strength criterion in practical geotechnical engineering.

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