One such problem is stress concentration caused by sudden change in form of machine elements 4. The problem of stressconcentration effects, produced by holes and notches in bars under tension is, of interest to machine designers. Structures and materials section 7 stress concentration. Stress concentration factor, slotted bars, eccentricity. Geometric stress concentration factors shigley, fig. In design under fatigue loading, stress concentration factor is used in. Pdf determination of the stress concentration factor k t in a. The stress concentration in a body happens because of sudden change in the geometry of the body due to cracks, sharp corners, holes, decrease in the cross section area. Stress concentration 20022014 darrell socie, all rights reserved 2 of 63 stress concentration factor. 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.
There are different stress concentration factors for bending and torsional loads. The strain concentration and strain distribution at a notch are influenced by plane stress. Once the notch tip zone yields, strain concentration increases and stress concentration decreases. Statics strength and stress concentration factors mechanical. For any other purpose, you must verify and validate every aspect of your calculations on your own, thus accepting total reponsibility for whatever you are doing. Petersons stress concentration factors, third edition researchgate. Note that the design solution for the diameter of the shaft should be an iteration procedure at least two. Theoretical approaches, using elasticity or strength of material considerations, can lead to equations similar to the one shown above. Therefore for fatigue design one needs to have good estimates both of the stress concentration factor scf at the weld toe and of the induced forces in the bolts. In addition, k is dependent only on ratios of geometric. Pdf stress concentration at notches download ebook for free. The stress concentration factors correspond to the ratio of the maximum membrane stress at the hole to the membrane stress in the shell far from the hole. Published elastic stress concentration factors are shown to underestimate stresses in the root of a shoulder filleted shaft in bending by as much as 21 percent, and in tension by as much as forty percent. Stress concentrations in keyways and optimization of keyway.
Stress concentration factors and notch sensitivity lecture 4 engineering 473 machine design. For the new third edition, new material will be added covering finite element analyses of stress concentrations, as well as effective computational design. These sources are readily available and used widely. Photoelasticity is a visual method for viewing the full field stress distribution in a photoelastic. Pdf the stress concentration factor in a plate with a hole is very important for joints.
The numerical calculations are shown by points and the full lines are the curve fit to the data, see equation 24 fig. Stress concentration factors scfs at girth welds arise from geometrical misalignments when the pipes are fitted together. The difference in stress concentration factors between single and doublesided supports can be neglected. Top 15 items every engineering student should have. A textbook called fundamentals of machine component design and theres a textbook on metal fatigue that has various q factors. Stress concentration an overview sciencedirect topics. The stress concentration factor scf differs from one joint geometry to another. Section 7 stress concentration stress concentrations produced by discontinuities in structures such as holes, notches, and fillets will be introduced in this section. Other resources you can utilize to determine q include petersons stress concentration factors, shigleys textbook for mechanical engineering design. Stress concentration factors for circular, reinforced penetrations in pressurized cylindrical shells a dissertation presented to the faculty of the school of engineering and applied science university of virginia in partial fulfillment of the requirements for the degree doctor of philosophy civil engineering by james w. Petersons stress concentration factors free download pdf. In other words, materials are not used in applications where they will be subject to stresses above their yield strength.
Apr 06, 2017 stress concentration is the accumulation of stress in a body due to sudden change in its geometry. The width ratio bd is linked to the depth ratio through equation 22. Jun 17, 2010 structures and materials section 7 stress concentration 1. Stress concentration factor important parameter for the safety. Utilizing the birefringentcoating technique complemented with data from electricalresistance type of strain gages, the whole field stresses and stress co. These stress concentrations will be finetuned in successive iterations, once the details are known. However, once the stress states satisfy the yield condition of the material, the strain concentration factor deviates from the value of the stress concentration. During the design phase, there are multiple approaches to estimating stress concentration factors. The fatigue stress concentration factors for normal stress and shear stress are specified, respectively, as. State of stress and stress concentration stress concentration and perfect plasticity of steel for a material with perfect elastoplastic constitutive relation, once the peak stress reaches yield point, its stress will remain this value and the stress concentration factor will decrease. It is thus defined as a ratio of the highest stress in the element to the reference stress. Notch sensitivity and fatigue notch factor, k f the fatigue notch factor,k f,is not necessarily equal to the elastic stress concentration factor. 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.
Charts of theoretical stressconcentration factors k. Stress concentration factors for different geometric shapes are found by using experimental techniques like photoelasticity, grid methods, brittlecoating methods, and electrical straingauge methods. An object is stronger when force is evenly distributed over its area, so a reduction in area, e. Stress concentration factors of cold formed stainless. Jul 09, 2015 discontinuities in the components that lead to local increase of stress is referred to as stress concentration. There is no perfect and systematic strain concentration solution for a notch under elastic.
When engineers design parts for service, they do so with the mechanical properties of the material in mind. Effect of stress concentration on fatigue life continued so what effect does a stress riser have on fatigue life. Petersons stress concentration factorspetersons stress concentration factors, third edition. Stress concentration factor kt, is a dimensionless factor which is used to quantify how concentrated the stress is in a material.
As you can see the stress flow lines are more even in the slant edged, filleted, notchedgrooved design. What is stress concentration definition, causes, effects. The latter approach requires having a means for obtaining stress concentration factors. Determination of stress concentration factors on flat plates. Weld design and specification university of delaware. Petersons stress concentration factors, 3rd edition pdf free.
Useful solutions for standard problems thayer school of. Effect of stress concentrations on fatigue most things that we design have features such as holes, fillets, keyways, and other notch shapes that cause stresses to be elevated relative to the nominal stress in the region surrounding the notch. A stress concentration factor kt is a dimensionless factor that is used to quantify how concentrated the stress is in a material. When there is a sudden change in the geometry of the body due to cracks sharp corners, holes and decrease in the cross section area, then there is an increase in the localised stress near these cracks, sharp corners, holes, and decreased cross. The stress concentration factor, k, is defined as follows. Stress concentration factors for the fatigue design of. What are the methods of reducing stress concentration. Structures and materials section 7 stress concentration 1. Updated stress concentration factors for filleted shafts in. This is part of what makes fatigue life estimation difficult. It is defined as the ratio of the highest stress in the element to the reference stress.
They are actually determined based on the corresponding strains, which show a certain degree of advantages compared to the stresses van wingerde et al. Interacting stress concentration factors and their effect on fatigue of metallic aerostructures by david warren whitley a dissertation presented to the faculty of the. The combined effect of these misalignments induces a local secondary bending stress that augments the otherwise plain nominal stress in the pipe section, as the nominal bending moment and axial forces are transferred across the weld. Stress concentration factors for mechanical design ever j. Petersons stress concentration factors, 4th edition wiley. Several catalogs of stress concentration factors have been published. In many simple geometries, the stress concentration factor is defined for a range of geometries. The two experimental results are those of houghtan and rothwell. Strain concentration theory of elasticity and stress. This site is provided without any warranties of any kind, and for educational purposes only. Jan 20, 2014 in this work, by using the ratio of the radius of curvature of the stress concentrating feature to the minimum thickness as the only fitting variable, generalized equations for both the bending and tension stress concentration factors were obtained for two generalized models, the conic model and the ellipticarcfillet model, through fitting.
Fillet and groove stress concentrations springerlink. Because of the lack of accurate data on stress concentration factors for these cases it was decided to make some additional. Stress concentration factors of cold formed stainless steel. As a base for estimating the effect of other parameters we estimate the fatigue notch factor k f for zero mean stress and long life 106108 cycles. Measured stress concentration factors, or analysed with fem as described in app. Stress concentration stress concentrations for shoulders and keyways are dependent on size specifications that are not known the first time through the process. When q0, kf 1, that is, no fatigue stress concentration effect when q1, kfk, that is, fatigue stress concentration has equal value of geometric stress concentration factor. Since the stress is much higher in these areas than in the rest of the part, fatigue failures will usually initiate in these regions. Sep 17, 2016 one typical method is the neuber rule. Generalized equations for estimating stress concentration. A stress concentration often called stress raisers or stress risers is a location in an object where stress is concentrated. Stress concentration factor an overview sciencedirect topics. Substantially revised and completely updated, this book presents stress concentration factors both graphically and with formulas. Petersons stress concentration factors, fourth edition includes a thorough introduction of the theory and methods for static and fatigue design, quantification of stress and strain, research on stress concentration factors for weld joints and composite materials, and a new introduction to the systematic stress analysis approach using finite.
The mentioned design features will not cause stress concentration. Download stress concentration at notches ebook free in pdf and epub format. For this reason, it is called theoretical or geometric stress concentration factor. Pdf petersons stress concentration factors loa carter. Weld design and specification jim glancey, pe depts. Useful solutions for standard problems preface modelling is a key part of design. Reducing stress concentrations school of materials. Design stress concentration factors for keyways cutting keyways create stress concentrations in shafts. This is why it is a good idea to keep features that concentrate stress out of your design, if at all possible. Petersons stress concentration factors, 3rd edition wiley. Stress concentration is related to type of material, the nature of the stress, environmental conditions, and the geometry of parts. Bending stress measurements, or continuous beam analysis, or 3point bending, depending on manufacturers documentation.
The structural stress concentration factors in table 8. Stress concentration caused by sudden change in form. A study among undergraduates in pakistan kashif ud din khan head of department, lahore business school, the university of lahore shazia gulzar department of psychology, lahore business school, the university of lahore farzan yahya lahore business school, the university of lahore abstract. In the early stage, approximate modelling establishes whether the concept will work at all, and identifies the combination of material properties that maximize performance. Interacting stress concentration factors and their effect on.
The hot spot stress method is currently being used for the design against fatigue by crack propagation from the weld toes of tubular connections. These may be reduced by using key seats made with bull end. Stress concentration factors petersons 12 and mechanical engineering design shigley. Index to the stress concentration factors xvii preface for the third edition xxxiii preface for the second edition xxxv 1 definitions and design relations 1 1. Stress concentrations in keyways and optimization of. It is known that the applied loads on tubular joints cause stresses at certain points along the intersection weld to be many times the nominal stress acting in the members. Stress concentration factors for shafts and cylinders.
Stress concentration factors are given for various common discontinuities. The behavior of stress concentration factors of three holes located transversely on a flat plate, as expected, decreases as the relation between three times the diameter of the holes divided by the width. Read stress concentration at notches online, read in mobile or kindle. Strain concentration is influenced by plastic constraint, namely by the extension morphology of the plastic zone. The nominal stress at the reduced area is computed as shown on the graph and the actual stress. Concepts of stress and strain university of arizona. General values are also given for keyways, gear teeth, screw threads and welds. Stress concentration caused by sudden change in form a change in the geometric shape of a part gives rise to additional stress over and above the calculated stress, which is known as stress concentration. Petersons stress concentration factors establishes and maintains a system of data classification for all of the applications of stress and strain analysis and expedites their synthesis into cad applications.
Fatigue failure process fatigue behavior in mechanical components is associated with the application of reversed or fluctuating stress states as contrasted to static. Stress concentration design factor for bars with slots and holes md. Peterson, stressconcentration factors, wiley, new york, 1974, pp. The present paper describes photo elastic tests and strain measurements to determine these. Lesson 17 stress concentration factor problem youtube. Stress concentration design factors 1953 and stress concentration factors 1974. Geometric stress concentration factors can be used to estimate the stress amplification in the vicinity of a geometric discontinuity. If not possible, then keep them away from the areas of peak stress under load. Approximate stressconcentration factors k ts for a round bar or tube having a transverse round hole and loaded in torsion source. Stress concentration factor theories of elastic failure strength of materials. The keyway related stress is indeed fully three dimensional as also stated in peterson 18. While it is often assumed that once the bolts are preloaded they are exempt from the fatigue.
T d a t d the maximum stress occurs on the inside of the hole, slightly below the shaft surface. Thus, the stress concentration factor increases as the radius of curvature in the. The stress concentration factor is defined as the ratio of highest stress in the body to the reference stress. It also employs computergenerated art in its portrayal of. Lesson 50 introduction to beam design example problem. 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 concentration produced by holes and notches by a. A number of different factors will have an influence on the needed fe. Dd 2 conclusions for the bending case of bars and shafts with central enlarged sections of width d and length l the factor of stress concentration, k, is a function of lid in addition to the other two parameters rd and dd which govern in the. Corrosionpedia what is a stress concentration factor kt. Approximate stressconcentration factors kts for a round bar or tube having a transverse round hole and loaded in torsion source. The stress concentration and stress state of tubing and casing thread connection should be considered in design in light of sour environments. The value of the sensitivity index of a material depends on two factors, the type of the material and its micro structure.
The chart below shows the curves of these factors and the dependency on the ratios of the critical dimensions. Stress concentration factor an overview sciencedirect. The stress concentration factors are widely used to predict the maximum stress value above which the mechanical structure can be destroyed, thus the two most common occurrence of stress concentrations are due to discontinuities in continuum and. Numerical analysis of stress concentration factors in order to verify the accuracy of the alfak soft ware, analysis of stress concentration factor was performed using numerical analysis in catia. Dnvglcg0037 calculation of crankshafts for reciprocating.
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