L convenient to think of kf as a stress concentration factor reduced from kt because of lessened sensitivity to notches. A stressconcentration factor is then applied to the data of box 3 and combined with the palmgrenminer damage rule and a material sn curve to yield the annual cumulative damage, d, and fatigue life of 1d years. Stress concentration caused by sudden change in form. Theories of failure and stress concentration effects 7. It is therefore logical to consider the extensive number of different ways in which components can fail. Under plastic deformation, the ratio of maximum stress to nominal stress. Estimation of plastic stress concentration factor around. The main reason for this is considered to be that k e is essentially based on only two parameters stress level and kind of material. Plastic stress and strain concentration factors in a strip. Stress concentrations locally high stresses can arise due to abrupt changes in section properties hole, corner contact stresses bearing, gear, etc material discontinuities initial stresses due to manufacturing process. The stress concentration factor is independent from materials made up the element but geometry, notch sensitivity, on the contrary, is material factor which is used to predict the fatigue strength of structural element. Charts of theoretical stressconcentration factors k. Transition of dislocation nucleation induced by local. Lecture notes mechanics and materials ii mechanical.
A study of elastic and plastic stress concentration. Further reading useful solutions for standard problems mike ashby engineering department trumpington street, cambridge cb2 1pz, uk 8th edition, march 2010. Derive of stress concentration factor formula in the zone of elastic plastic strain. Approximate stressconcentration factor kt for bending of a round bar or tube with a transverse round hole source.
Degree thesis stress concentration analysis of materials. Stress concentration factor k t k t is difficult to calculate and it is usually determined by some experimental technique photoelastic analysis of a plastic model or by numerical simulation of the stress field. Problems of strain concentration in an elastic state are equivalent to those of elastic stress concentration. In monotonic loading, the plastic concentration factor formulation is evaluated using the virgin stressstrain curve of the material.
The strain gauge consists of a grid of strainsensitive metal foil bonded to a plastic backing material. Fatigue stress concentration factors lkf is normally used in fatigue calculations but is sometimes used with static stresses. With the use of j 2 deformation theory, the stressconcentration factor at a circular hole in an infinite sheet of strainhardening material subjected to equal biaxial tension at infinity is found for a variety of representative materials. Notch sensitivity and fatigue notch factor, k f the fatigue notch factor,k f,is not necessarily equal to the elastic stress concentration factor. In this work, stress concentration factors both elastic and plastic near the elliptical cut outs of various standard geometries and for different material are computed using fea and a comparison is made with analytical and semiempirical methods available which demonstrates the behaviour of the structures with cut outs in the plastic regime. The calculated discrepancy between the geometric mean of the plastic stress and strain concen. A generalization of neubers rule for numerical applications. A stress concentration also called a stress raiser or a stress riser is a location in an object where the stress is significantly greater than the surrounding region. The results showed further that the stress concentration factor decreases as strains at the discontinuity enter the plastic range. A study of elastic and plastic stress concentration factors due to notches and fillets in flat plates. Strain concentration theory of elasticity and stress. L if notch sensitivity data is not available, it is conservative to use kt in fatigue calculations.
Peterson, stressconcentration factors, wiley, new york, 1974, pp. On the basis of the local shear stress near the step and in the grain interior, a stress concentration factor k is estimated as k i. The degree of stress and strain concentration is a factor in the fatigue strength. The analysis exploits a transformation which permits the calculation of the stressconcentration factor without determining the stress distribution in the. A study of elastic and plastic stress concentration factors due to. A stress concentration factor is then applied to the data of box 3 and combined with the palmgrenminer damage rule and a material sn curve to yield the annual cumulative damage, d, and fatigue life of 1d years. Fatigue fracture was associated with the cyclic plastic strain range and the total energy. Stress concentration factors of cold formed stainless. The plastic strain range, a plastic strain and stress concentration factors for notched specimens nominal kt 3 of carbon steel, 2. A generalization of stowells relation for the plastic stress concentration factor at a circular hole in an infinite plate was applied to the specimen shapes tested and gave good agreement with test results.
Plastic stress and strain concentration factors in a strip with a hole or notches under tension. A new concept for plastic strain concentration factors. Detailed elastoplastic analyses showed that the plastic strain concentration factor k e of the asme code is usually overly restrictive, but may also be unconservative. The most popular method to estimate the approximate value. In this paper, the influence of the geometry of the structure and of the kind of. Plastic failure through environmental stress cracking.
Environmental stress cracking can take place through continuous crack growth or via a stepwise progressive mechanism of cracking and arrest, depending on the molecular structure of the plastic, the composition of the chemical agent, the level. Stress concentration factor an overview sciencedirect. Stress concentration factor electrical strain gauges the method is the most popular and widely accepted for strain measurements and stress analysis. Mechanical engineers reference book twelfth edition, 1994. As a result of this, designing with brittle materials, it requires the use of geometric stress concentration factors to determine the actual stress at a point, for all kinds of loading situations. Find materials for this course in the pages linked along the left. Pdf for the assumed computing model the simple explicit formula for fast. Stress concentrations occur when there are irregularities in the geometry or material of a structural component that cause an interruption to the flow of stress. The stress concentration factor is derived using the theory of elasticity, computational calculations e. If this maximum stress becomes plastic, stress relaxation occurs and the elastoplastic stress concentration is less than the elastic one. R, which produces plastic deformation that result from application of a simple tensile stress. Fatigue strength influence of surface so far special mirror polish surface only in laboratory. Plasticity corrections for elastic analysis results. However, once the stress states satisfy the yield condition of the material, the strain concentration factor deviates from the value of the stress concentration.
Abstractspread of plastic region and influence of severity of constraint are observed and concentration factors are evaluated by photoplasticity of celluloid. Useful solutions for standard problems dartmouth college. The more abrupt the transition, the higher are the stress concentrations. The one on the left side is the stabilized cyclic stressstrain curve generally derived from uniaxial fatigue test samples, while on the right is the same curve with coordinates multiplied by a factor of two. As a base for estimating the effect of other parameters we estimate the fatigue notch factor k f for. The localized plastic deformation and notch blunting effect due to yielding at the. The subscript t indicates that the stress concentration factor is a theoretical factor. Plastic stress concentration at a circular hole in an. In this video i present a basic look at the field of fracture mechanics, introducing the critical stress intensity factor, or fracture toughness. Chapter outline dislocations and strengthening mechanisms. Stress concentration occurs at transition of cross sections. A stress concentration at end of a slip plane may trigger new dislocations in an adjacent grain. Thus, the stress concentration factor increases as the radius of curvature in the.
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