FKM - commentary

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<p>1</p> <p>FKM-Guideline ANALYTICAL STRENGTH ASSESSMENT OF COMPONENTS IN MECHANICAL ENGINEERING5th, revised edition, 2003, English Version Translation by E. Haibach</p> <p>Title of the original German Version: RECHNERISCHER FESTIGKEITSNACHWEIS FR MASCHINENBAUTEILE 5., berarbeitete Ausgabe, 2003</p> <p>Editor: Forschungskuratorium Maschinenbau (FKM)Postfach 71 08 64, D-60498 Frankfurt / Main Phone 49 - 69 - 6603 - 1345</p> <p>2</p> <p>Preface of the English Version of the 5th Edition.For engineers concerned with construction and calculation in mechanical engineering or in related fields of industry the FKM-Guideline for analytical strength assessment is available since 1994. This guideline was elaborated by an expert group "Strength of components" of the Forschungskuratorium Maschinenbau (FKM), Frankfurt/Main, with financial support by the Bundesministerium fr Wirtschaft (BMWi), by the Arbeitsgemeinschaft industrieller Forschungsvereinigungen Otto von Guericke" and by the Forschungskuratorium Maschinenbau. Based on former TGL standards and on the former guideline VDI 2226, and referring to more recent sources it was developed to the current state of knowledge. The FKM-Guideline - is applicable in mechanical engineering and in related fields of industry, - allows the analytical strength assessment for rod-shaped (1D), for shell-shaped (2D) and for block-shaped (3D) components under consideration of all relevant influences, - describes the assessment of the static strength and of the fatigue strength, the latter according to an assessment of the fatigue limit, of the constant amplitude fatigue strength, or of the variable amplitude fatigue strength according to the service stress conditions, - is valid for components from steel, cast steel, or cast iron materials at temperatures from -40 C to 500 C, as well as for components from aluminum alloys and cast aluminum alloys at temperatures from -40 C to 200 C, - is applicable for components produced with or without machining, or by welding, - allows an assessment in considering nominal stresses as well as local elastic stresses derived from finite element or boundary element analyses, from theoretical mechanics solutions, or from measurements. A uniformly structured calculation procedure applies to all of these cases of application. The calculation procedure is almost completely predetermined. The user has to make some decisions only. The FKM-Guideline is a commented algorithm, consisting of statements, formulas, and tables. Most of the included figures have an explanatory function only. Textual declarations are given where appropriate to ensure a reliable application. Its content complies with the state of knowledge to an extend that may be presented in a guideline and it enables quite comprehensive possibilities of calculation. The employed symbols are adapted to the extended requirements of notation. The presented calculation procedure is complemented by explanatory examples. Practically the described procedure of strength assessment should be realized by means of a suitable computer program. Presently available are the PC computer programs "RIFESTPLUS" (applicable for a calculation using elastically determined local stresses, in particular with shell-shaped (2D) or block-shaped (3D) components) and "WELLE" (applicable for a calculation using nominal stresses as it is appropriate in the frequently arising case of axles or shafts with gears etc).</p> <p>3 The preceding editions of the FKM-Guideline observed a remarkably great interest from which the need of an up to date guideline for analytical strength analyses becomes apparent. Moreover the interest of users was confirmed by the well attended VDI conferences on "Computational Strength Analysis of Metallic Components", that were organized for presentation of the FKM-Guideline at Fulda in 1995, 1998 and 2002. The contents-related changes introduced with the third edition from 1998 were mainly concerned with the consideration of stainless steel and of forging steel, with the technological size factor, with the section factor for assessing the static strength, with the fatigue limit of grey cast iron and of malleable cast iron, with additional fatigue classes of welded structural details and with the local stress analysis for welded components, with the specification of an estimated damage sum smaller than one for the assessment of the variable amplitude fatigue strength, with the assessment of multiaxial stresses, and with the experimental determination of component strength values. An essential formal change in the third edition was a new textual structure providing four main chapters, that describe the assessment of the static strength or of the fatigue strength with either nominal stresses or local stresses, respectively. For ease of application each of these chapters gives a complete description of the particular calculation procedure, although this results in repetitions of the same or almost the same parts of text in the corresponding sections. The major change in the forth edition from 2002 is the possibility of considering structural components made from aluminum alloys or cast aluminum alloys by applying the same calculation procedure that was developed for components from steel, cast steel and cast iron materials so far. The decisions necessary to include aluminum materials were derived from literature evaluations. It had to be recognized, however, that some of the relevant factors of influence were not yet examined with the desirable clearness or that available results could not be evaluated objectively due to large scatter. In these cases the decision was based on a careful consideration of substantial relations. Concerning an analytical strength assessment of components from aluminum alloys or from cast aluminum alloys this guideline is delivered to the technical community by supposing that for the time being it will be applied with appropriate caution and with particular reference to existing experience so far. The involved research institutes and the Forschungskuratorium Maschinenbau (FKM) will appreciate any reports on practical experience as well as any proposals for improvement. Further improvements may also be expected from ongoing research projects concerning the procedure of static strength assessment using local elastic stresses, Chapter 3, and the fatigue assessment of extremely sharp notches. Last not least the fifth edition of the FKM-Guideline is a revision of the forth edition and it is presented in both a German version and an English version with the expectation that it might observe similar attention as the preceding editions on a broadened international basis of application.</p> <p>4 Notes of the translator The English translation is intended to keep as close as possible to the original German version, but by using a common vocabulary and simple sentences. If the given translation is different from a literal one, the technical meaning of the sentence and/or of the paragraph is maintained, however. The translation observes an almost identical structure of the headlines, of the chapters, of the paragraphs and of the sentences, and even of the numbering of the pages. Also the tables and the figures as well as their numbering and headlines are adapted as they are, while only the verbal terms have been translated. In particular the original German notation of the mathematical symbols, indices and formulas, as well as their numbering, has not been modified in order to insure identity with the German original in this respect. The applier of this guideline is kindly asked to accept the more or less unusual kind of notation which is due to the need of clearly distinguishing between a great number of variables. In particular the applier is pointed to the speciality, that a comma ( , ) is used with numerical values instead of a decimal point ( . ), hence 1,5 equals 1.5 for example.</p> <p>5</p> <p>ContentsPage 0 0.1 0.2 0.3 1 1.0 1.1 1.2 1.3 1.4 1.5 1.6 2 2.0 2.1 2.2 2.3 2.4 2.5 2.6 3 3.0 3.1 3.2 3.3 3.4 3.5 3.6 4 4.0 4.1 4.2 4.3 4.4 4.5 4.6 General survey Scope Technical background Structure and elements Assessment of the static strength using nominal stresses General Characteristic stress values Material properties Design parameters Component strength Safety factors Assessment Assessment of the fatigue strength using nominal stresses General Parameters of the stress spectrum Material properties Design Parameters Component strength Safety factors Assessment Assessment of the static strength using local stresses General Characteristic stress values Material properties Design parameters Component strength Safety factors Assessment Assessment of the fatigue strength using local stresses General Parameters of the stress spectrum Material properties Design parameters Component strength Safety factors Assessment 97 103 106 113 125 127 73 76 85 89 90 93 41 47 50 57 68 70 19 22 30 33 34 36 9</p> <p>6</p> <p>Page 5 5.1 5.2 5.3 5.4 5.5 5.6 5.7 5.8 5.9 5.10 5.11 5.12 6 6.1 6.2 6.3 6.4 6.5 6.6 7 7.1 7.2 7.3 7.4 7.5 7.6 8 Appendices Material tables Stress concentration factors Fatigue notch factors Fatigue classes (FAT) for welded components of structural steel and of aluminum alloys Comments about the fatigue strength of welded components of structural steel Adjusting the stress ratio of a stress spectrum to agree to that of the S-N curve and deriving a stepped spectrum Assessment using classes of utilization Particular strength characteristics of surface hardened components An improved method for computing the component fatigue limit in the case of synchronous multiaxial stresses Approximate assessment of the fatigue strength in the case of non-proportional multiaxial stresses Experimental determination of component strength values Stress concentration factor for a substitute structure Examples Shaft with shoulder Shaft with V-belt drive Compressor flange made of grey cast iron Welded notched component Cantilever loaded by two loads Component made of a wrought aluminum alloy Symbols and basic formulas Abbreviations Indices Lower case characters Upper case characters Greek alphabetic characters Basic formulas Subject index 259 260 261 262 263 231 236 241 245 250 256 131 178 187 195 209 216 218 222 223 226 227 230</p> <p>7</p> <p>0 General survey0.1 ScopeThis guideline is valid for components in mechanical engineering and in related fields of industry. Its application has to be agreed between contracting parties. For components subjected to mechanical loadings it allows an analytical assessment of the static strength and of the fatigue strength, the latter as an assessment of the fatigue limit or of the variable amplitude fatigue strength according to the service stress conditions. Other analytical assessments, for example of safety against brittle fracture, of stability, or of deformation under load, as well as an experimental assessment of strength *1, are not subject of this guideline. It is presupposed, that the components are professionally produced with regard to construction, material and workmanship, and that they are faultless in a technical sense. The guideline is valid for components produced with or without machining or by welding of steel, iron or aluminum materials that are intended for use under normal or elevated temperature conditions, and in detail for components with geometrical notches, for components with welded joints, for static loading, for fatigue loading with more than about 104 constant or variable amplitude cycles, - for milled or forged steel, also stainless steel, cast iron materials as well as aluminum alloys or cast aluminum alloys, - for component temperatures from 40C to 500C for steel, from 25C to 500C for cast iron materials and from 25C to 200C for aluminum materials, - for a non-corrosive environment. If an application of the guideline is intended outside the mentioned field of application additional specifications are to be agreed upon. The guideline is not valid if an assessment of strength is required according to other standards, rules or guidelines, or if more specific design codes are applicable, as for example for bolted joints.</p> <p>0.2 Technical BackgroundBasis of the guideline are the references listed on page 7, in particular the former TGLStandards, the former VDI-Guideline 2226, as well as the regulations of DIN 18 800, the IIW-Recommendations and Eurocode 3. Moreover the guideline was developed to the current state of knowledge by taking into account the results of more recent investigations.</p> <p>1 Subject of Chapter 5.11 "Experimental determination of component strength values" is not the realization of an experimental assessment of strength, but the question how specific and sufficiently reliable component strength values suitable for the general procedure of strength assessment may be derived experimentally.</p> <p>8</p> <p>0.3 Structure and elementsContents 0.3.0 0.3.1 0.3.2 General Procedure of calculation Stress parameters 11 Page 9 10</p> <p>0.3.3 Methods of strength assessment 0.3.3.0 General 0.3.3.1 Assessment of the static strength using nominal stresses, Chapter 1 0.3.3.2 Assessment of the fatigue strength using nominal stresses, Chapter 2 0.3.3.3 Assessment of the static strength using local stresses, Chapter 3 0.3.3.4 Assessment of the fatigue strength using local stresses, Chapter 4 0.3.4 0.3.4.0 0.3.4.1 0.3.4.2 0.3.4.3 0.3.5 Kinds of components General Rod-shaped (1D) components Shell-shaped (2D) components Block-shaped (3D) components Uniaxial and multiaxial stresses</p> <p>12</p> <p>13 13 14 15 16</p> <p>0.3.0 General An assessment of the static strength is required prior to an assessment of the fatigue strength. Before applying the guideline it has to be decided - what cross-sections or structural detail of the component shall be assessed *2 and - what service loadings are to be considered. The service loadings are to be determined on the safe side, that is, with a sufficient probability they should be higher than most of the normally occurring loadings *3. The strength values are supposed to correspond to an anticipated probability of 97,5 % (average probability of survival P = 97,5 %).</p> <p>2 In particular, what critical points of the considered cross-sections or component. 3 Usually this probability can hardly be quantified, however.</p> <p>9 0.3.1 Procedure of calculation The procedure of calculation for an assessment of the static strength is presented in Figure 0.0.1, the almost identical procedure for an assessment of the fatigue strength in Figure 0.0.2 *4.</p> <p>Figure 0.0.1 Procedure of calculation for an assessment of the static strength.</p> <p>Figure 0.0.2 Procedure of calculation for an assessment of the fatigue strength.</p> <p>4 A more detailed survey on the procedures of assessment referring to the equations of the guideline may be found in the Appendix, Chapter 7.6.</p> <p>10 At the assessment stage (box at bottom of either Figure) the characteristic values of service stress occurring in the component (box at top on th...</p>