Estimating reliability in a strengthstress interference. In section 3, stressstrength interference is considered. The variation in stress and strength results in a statistical distribution and natural scatter occurs in these variables when the two distributions interfere. Dynamic model ing of stressstrength interference might offer more realistic.
Probability density function failure probability effective sample size joint probability density function fatigue reliability these keywords were added by machine and not by the authors. Along the radial direction from inside to outside, stress decreases gradually, and the maximum stress is 339 mpa. The derivation of equation 710 is same as equation 79, whereas the difference is that the strength is set to r 0, falling into the interference area first. Application of the stressstrength interference model to the design. Reliability analysis based on stressstrength interference model. The stress decreased with the decreasing relative interference due to decreasing rivet nail rod expansion. The model calculates the probability of failure by determining the probability that a random stress drawn from a stress distribution is greater than a random strength drawn from a strength. Pdf comparative analysis of toothroot strength using. Stressstrength interference model has been widely used for reliability analysis of structures.
Publication date 1989 publisher kansas state university collection. A 400 mm od steel cylinder with a nominal id of 240 mm is shrunk onto another steel cylinder of 240 mm od and 140 mm id. This article introduces the concept of the stressstrength interference model for reliability. This interference ensures that the pin will be placed in compression by the additional expansion of the bell during insertion. Useful solutions for standard problems dartmouth college. Interference assembly and fretting wear analysis of hollow. As we know, the expected reliability is called from the following stressstrength calculation. Then, according to stressstrength interference theory and the theory of the order statistics, the reliability models considering the number of load cycles from a gear to gear system are built. For mechanical components, reliability can be predicted using the stressstrength interference and probabilistic design method.
Full text of stressstrength interference models in. However, a complex dependence between stress and strength exists in practical engineering. The stress distribution is usually estimated from customer usage data, such as the mileage per year of a passenger car or the load distribution for a beam. The stressstrength interference method applied to fatigue design. In addition to the spin stresses, interference fit preload stresses contribute to the loading of the core material.
Seeing this let y and x be two random variables such that y represents strength and x represents stress and let y, x follow a joint probability density function pdf. Stress and strength distribution example reduced strength variability using the quarter interference stressstrength analysis calculator, the probability of failure is now calculated to be 0. Stressstrength models to estimate systems reliability rt. Computational method for importance measure of the kout. A major drawback is the assumption that the strength and stress are statistically independent, which may not be valid for some problems. We study the stressstrength reliability for the case in which the strength of the system is decreasing in time and the stress remains fixed over time. The stress distribution at the interface of interference fitted assemblies depends on various parameters such as amount of interference, physical dimensions, material properties, diameter and contact length, geometrical inaccuracies and surface roughness of mating members. Although more powerful methods of reliability analysis.
In a strengthstress interference model we are interested in estimating the reliability, here we present two results. The mathematical formulation for the stressstrength. A dependent stressstrength interference model based on. Stressstrength interference models in reliability core. Pdf extension of stress and strength interference theory. Based on systemlevel stressstrength interference model, a new computational method for the birnbaum importance measure is proposed for the koutofn system. Stress strength analysis is the analysis of the strength of the materials and the interference of the stresses placed on the materials, where materials is not necessarily the raw goods or parts, but can be an entire system. Therefore r py stressstrength analysis calculator, the probability of failure is now calculated to be 0.
Part i fast fracture, probabilistic engineering mechanics, 7, 1992, p. Note that several errors in the source material have been corrected. Methods of estimating stressstrength interference reliability under a time dependent degradation analysis by nandan sudarsanam bachelor of engineering bharathidasan university tiruchirapalli, india 2003 submitted to the faculty of the graduate college of the oklahoma state university in partial fulfillment of the requirements for the degree of. Stressstrength interference models in reliability by lee, anmin.
This calculator will determine a variety of force, stress and other design parameters for press fit applications. Due to residual tensile and compressive stresses, the stress and strain in the material does not. The word interference refers to the fact that one part slightly interferes with the space that the other is taking up. Stressstrength interference is a model to predict the probability of failure when the probability distributions of the stress and the strength are known. In other words, when probability density functions of both stress and strength are known, the component reliability may be determined analytically. On stressstrength reliability with a time dependent strength. On stressstrength reliability with a timedependent strength. To evaluate the structure reliability in the case of strength degradation over time, the strength degradation is represented by a gamma process and the stress applied on a structure is represented by the poisson process in. Stressstrength analysis is the analysis of the strength of the materials and the interference of the stresses placed on the materials, where materials is not necessarily the raw goods or parts, but can be an entire system. This study addressed itself to the development of a practical engineering tool based on the stressstrength interference theory to be used for designing and quantitatively predicting the reliability of mechanical parts subjected to mechanical loading.
Computation of reliabilityenlarged portion of the interference area. The stress and strength curves would then be as shown in figure 3. Strength degradation of a structure is a common phenomenon in engineering. In order to derive the maximum benefit by the use of interferencefit pin in all. Extension of stress and strength interference theory for conceptual designforreliability article pdf available in journal of mechanical design 17 july 2009 with 335 reads. The stressstrength interference method is one of the oldest methods of structural reliability analysis. An interference fit, also known as a press fit or friction fit, is a fastening between two parts which is achieved by friction after the parts are pushed together, rather than by any other means of fastening. This article deals with the importance measure for the koutofn system of which components are loaded by common stress. Stressstrengthinterferencemodels in reliability by anminlee b. If this assumption can be justified, then reliability can be computed relatively quickly, using stressstrength interference methods. Stressstrength analysis is the analysis of the strength of the materials and the interference of. Pdf the stressstrength interference method applied to fatigue. This process is experimental and the keywords may be updated as the learning algorithm improves. This work was simple to implement, giving the failure probability with a quite acceptable computational time and providing useful information with regard to the quantification of the failure probability of the component.
An interference fit is generally achieved by shaping the two mating parts so that one or the other, or both, slightly deviate in size from the nominal dimension. Stressstrength analysis is a tool used in reliability engineering environmental stresses have a distribution with a mean and a standard deviation and component. Introduction interferencefit pin connections have wide applications ranging from aerospace structures to electric hardware systems and the telephone industry. Interference theory an overview sciencedirect topics. Interference fit, stress analysis,fem,contact stress. Pdf the use of the probabilistic analysis called stressstrength interference method ssim applied to the endurance limit approach is being analyzed find. When interference becomes higher than strength, failure results. It is this compressive load applied over the joint engagement area in the presence of.
Stress strength interference free download as pdf file. Where, fy is the probability density function pdf of stress y and fx is the. The beam is no longer elastic, and, in this sense, has failed. If, instead, the maximum fiber stress reaches the brittle fracture strength. This method assumes that the material properties are time independent because of their slow change, and the components are. The use of the probabilistic analysis called stressstrength interference method. In the traditional stressstrength interference ssi model, stress and strength must satisfy the basic assumption of mutual independence. The enlarged interference area is shown in figure 3. Effect of interference fit size on tensile strength and. The fibre stress changed from compression stress to tensile stress since the bending stresses transmitted to this region.
The stressstrength concept in practice accendo reliability. Effect of the interference fit on the stress distribution. Methods that consider stress and fatigue strength as random variables and basing the reliability of structural strength on stressstrength interference theory are widely used. Compressive residual stress induced by interferencefit can reduce the effective hoop stress at the. Stressstrength interference for normal distributions. To evaluate structural reliability under the case that stress and strength are dependent, a mixed copula function is introduced to a new dependent ssi model. Design and stress analysis of a high speed rotor for an. The study of stressstrength reliability in a timedependent context needs to model at least one of the stress or strength quantities as dynamic. Press fit forces stress design calculator engineers edge. Fatigue data were gathered for various ferrous materials, heat treatments, surface conditions, etc.
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