Assessment of maximum crack size a

(1) This will usually be determined on the basis of net section ductile tearing under the maximum applied tensile load with the appropriate partial factor (see Part 1 of this Prestandard). For further information on fracture toughness see References B.8.1 and B.8.2. b) mk value for weld toe stress concentration Figure B.4.1. Use of typical standard geometry solutions for y

Calculations for initial crack length aj based on Annex B fatigue crack growth rate data FCGR and the fatigue reference

(1) The calibrated initial fatigue crack length, aj, were determined for the fatigue reference stress ranges at 2 million cycles in case of (1) a uniform tension and (2) a stress gradient. The proposed conservative envelope of the fatigue crack growth curves as shown in Figs.B.3.3-B.3.5 and listed in tables B.3.3 to B.3.5 were used. The fracture mechanics model was a half disk surface crack in a 12mm thick and 200mm wide plate subjected to the two loading cases (see Fig.B.7.1). Figure B.7.1....

Crack growth data A and m

(1) A and m are obtained from crack growth measurements on standard notched specimens orientated in the LT, TL or ST direction (e.g. see Figure B.3.1) using standardised test methods (e.g. see Reference B.8.3). The specimen design must be one for which an accurate stress intensity factor (K) solution (i.e. the relationship between applied load and crack size 'af) is available. Recommended thickness w 20 < b< w 4 Recommended thickness w 20 < b< w 4 Fig.B.3.1. Typical crack growth...

Geometry Function y

(1) The geometry function y is dependent on the crack dimension (shape and size), the boundary dimensions of the surface of the surrounding material and the stress pattern in the region of the crack path. (2) This information can be obtained from finite element analyses of the detail using crack tip elements. The stress intensity for different crack lengths is calculated using the J integral procedure. Alternatively it can be calculated from the displacement or stress field around the crack...

Integration of crack growth

(1) For the general case of a variable amplitude stress history, a stress spectrum has to be derived (see 2.2). In practice the complete spectrum should be applied in at least 10 identical sequences with the same stress ranges and R ratios, but with one tenth of the number of cycles. The block with the greatest amplitude should be applied first in each sequence (see Figure.4.5.1). The incremental crack growth is calculated using the crack growth polygon for the appropriate R ratio, for each...

References

B.8.1 AW guidance on assessment of the fitness for purpose of welded structures. IIW Draft for Development doc. SST-1157-90. B.8.2 Guidance on some methods for the derivation of acceptance levels for detects in fusion welded joints. British Standard Published Document 6493 1991. B.8.3 Standard test method for measurement of fatigue crac k growth rates, ASTM E647-93. B.8.4 Fatigue crack propagation in aluminium, IIW Document XIII-B77-90. B.8.5 Stress intensity factor equations for cracks in...

Background to the Eurocode Programme

The Commission of the European Communities (CEC) initiated the work of establishing a set of harmonized technical rules for the design of building and civil engineering works which would initially serve as an alternative to the different rules in force in the various Member States and would ultimately replace them. These technical rules became known as the Structural Eurocodes. In 1990, after consulting their respective Member States, the CEC transferred the work of further development, issue...

Determination of Required Quality Level

(1)P The detail categories in tables 5.1.1 to 5.1.5 represent the maximum fatigue strength permitted by this code for the detail in question when manufactured to the quality requirements of Annex D, and shall not be exceeded without further substantiation by test (see Annex C). (2)P The higher class details often require additional inspection and demand higher workmanship standards (see Annex D), which can have an adverse effect on the economy of manufacture. Inspection and workmanship...

Distinction Between Principles and Application Rules

(1) Depending on the character of the individual clauses, distinction is made in this Eurocode between Principles and Application Rules. - general statements and definitions for which there is no alternative, as well as - requirements and analytical models for which no alternative is permitted unless specifically stated. (3) The Principles are identified by the letter P following the paragraph number. (4) The Application Rules are generally recognised rules which follow the Principles and...

Machining or grinding

(1) Machining can be performed by a high speed rotaiy burr cutter and has the advantages of producing a more precise radius definition, leaving marks parallel to the stress direction and gaining access to corners. Alternatively a disk grinder may be used if access permits, see Figure E.2.1. In both cases the radius of the cutting tip or edge must be correctly chosen. (2) To ensure the removal of intrusions etc. burr machining has to be extended to a depth of minimum 0.5mm below the bottom of...

Effect of Mean Stress General

(1) The fatigue strength data given in 5.2 refer to high tensile mean stress conditions. Where the mean stress is compressive or of low tensile value the fatigue life may be enhanced under certain conditions. See 5.3.2 to 5.3.6 and Annex G for further guidance. 5.3.2 Plain material and mechanically fastened joints (1) Provided that the effects of tensile residual and lack of fit stresses are added to the applied stresses, the fatigue enhancement factor given in Annex G may be considered. (1)P...

Test Data

(1) Table F.3.1 gives values of mo for selected details in certain wrought alloy products which have been derived from test data. (2) For R-ratios between R -1 and R 0 a linear interpolation of inverse mo value may be used. (3) The R-value may be based on the applied stresses only without taking into account residual stresses. Sheet and plate Sheet and plate Shaped extrusions Shaped extrusions

Fitnessfor Purpose Assessment

(1) In the event that there is a marginal non-conformity with the quality requirements in Annex D and that correction would be a) detrimental to the integrity of the structure, or b) an engineering critical assessment (ECA) may be undertaken and have serious economic consequences, the following information will be needed a) The static and cyclic stressing requirements at the detail concerned b) The dimensions of the defect c) The material properties in the region of the defect (2) The fatigue...

Enhancement Cases G Case

(1) This applies to initiation sites in base material and wrought products in structural elements remote from connections. It may also be applied to structures which have been effectively stress relieved. (2) Allowance shall be made for any pre-load or lack of fit in addition to the applied stresses. (3) The values of f(R) are given in table G.2.1. and fig. G.2.1. Table G.2.1. Values of f(R) for Case 1 Table G.2.1. Values of f(R) for Case 1 Figure G.2.1. Strength enhancement factor f(R) at 2...

Global Stress Analysis

(1)P The method of analysis shall be selected so as to provide an accurate prediction of the elastic stress response of the structure to the specified fatigue loading. NOTE An elastic model used for static assessment (ultimate or serviceability limit state) in accordance with Part 1.1 of this Prestandard may not necessarily be adequate for fatigue assessment. (2)P Dynamic effects shall be included in the calculation of the stress history, except where an equivalent loading is being applied...

Improvement Techniques

(1) The fatigue strength of certain detail types shown in tables 5.1.1 to 5.1.5 may be improved by the application of special manufacturing techniques. These are generally expensive to apply and present quality control difficulties. They should not be relied upon for general design purposes, unless fatigue is particularly critical to the overall economy of the structure, in which case specialist advice should be sought. They are more commonly used to overcome existing design deficiencies. (2)...

Info

F) Damage summation (Palmgren-Miner rule) Jh fh Jh h _ n A A 2+ A a Nr l Figure 2.2.1. Fatigue assessment procedure (3)P The fatigue crack initiation sites determined in (2) shall be on or close to a surface which shall be readily accessible in service. The only exception shall be where safe alternative load paths are provided and details are designed to ensure that the cracks will be arrested without propagation beyond the first load path. (4)P The procedure in 2.3.2 shall be applied to...

Objectives of the Eurocodes

The Structural Eurocodes comprise a group of standards for the structural and geotechnical design of buildings and civil engineering works. They are intended to serve as reference documents for the following purposes a) As a means to prove compliance of building and civil engineering works with the essential requirements of the Construction Products Directive (CPD). b) As a framework for drawing up harmonised technical specifications for construction products. They cover execution and control...

Safe Life Design

2.2.1 Prerequisites for safe life design (1)P The predicted service history of the structure shall be available in terms of a loading sequence and frequency. Alternatively the stress response at all potential initiation sites shall be available in terms of stress histories. (2) P The fatigue strength characteristics at all potential initiation sites shall be available in terms of fatigue strength curves. (3)P The quality standards used in the manufacture of the components containing potential...

Scope of Eurocode Part

(1) This Part 2 gives the basis for the design of aluminium alloy structures with respect to the limit state of fatigue induced fracture. Design for other limit states is covered in Part 1. (2) This Part 2 gives rules for design by the following methods (3) This Part 2 contains the manufacturing quality requirements necessary to ensure that the design assumptions are met in practice. - Beams and braced and unbraced framed structures - Stiffened plate structures of flat or shell construction (2)...

Sources of Fatigue Loading

(1)P All sources of fluctuating stress in the structure shall be identified. The following shall receive particular attention a) superimposed moving loads, including vibrations from machinery in stationary structures b) environmental loads such as wind, waves, etc. c) acceleration forces in moving structures (2)P The fatigue loading shall be obtained from ENV 1991 Eurocode 1 or other relevant loading standard, where available.

Effect of Environment

1 P The detail category Aac given in Tables 5.1.1 to 5.1.5 and 5.2.2 shall be reduced in accordance with Table 5.4.1 for certain combinations of alloy and environment where the average ambient temperature during the life does not exceed 65 C. NOTE For marine environment the average ambient temperature during the life should not exceed 30 C. Table 5.4.1 Number of detail categories by which Acc shall be reduced according to Table 5.4.1 Number of detail categories by which Acc shall be reduced...

Enhancement of fatigue strength

1 For applied stress ratio values less than R 0,5 the reference fatigue strength Aac may be enhanced by an R ratio factor f R where the enhanced reference fatigue strength Aa at 2 x 106 cycles is given by 2 The value of f R depends on the value of R and the type of component and detail see G.2 . 3 The fatigue strength at 104 cycles should not be enhanced. 4 The basic slope mi R of the enhanced Aa-N curves shall be adjusted in accordance with the values of Ac at 104 and 2 x 106 cycles see fig....

Fatigue Strength Data Classified details

1 P The generalised form of the Aa-N relationship is shown in figure 1.5.2, plotted on logarithmic scales. The design curve represents a mean minus 2 standard deviation level below the mean line through experimental data. 2 P The basic fatigue design relationship for endurances less than 5 x 106 cycles is defined by the equation Nj is the predicted number of cycles to failure of a stress range Acjj Aac is the reference value of fatigue strength at 2 x 106 cycles, depending on the category of...

Stress range parameters for specific Initiation Sites

4.4.1 Parent material, full penetration butt welds and mechanically fastened joints see Tables 5.1.5, 5.1.2, 5.1.3 and initiation sites 1,2,3,7 and 9 in Table 5.1.3 . 1 P Cracks initiating from weld toes, fastener holes, fraying surfaces, etc. and propagating through parent material or fully penetrated weld metal shall be assessed using the nominal principal stress range in the member at that point see Fig.4.2.1 . 2 P The local stress concentration effects of weld profile, bolt and rivet holes,...

Principles B Flaw dimensions

Planar Flaws Fatigue

1 Fatigue propagation is assumed to start from a pre-existing planar flaw with a sharp crack front orientated normal to the direction of principle tensile stress fluctuation Act at that point. 2 The dimensions of the pre-existing flaws are shown in Figure B.2.1 depending on whether they are surface breaking or fully embedded within the material. Figure B.2.1 Pre-existing planar flaws

Stress Spectra

Cycle Counting

1 Cycle counting is a procedure for breaking down a complex stress history into a convenient spectrum of cycles in terms of stress range A a, number of cycles n and, if necessaiy, R ratio see figure 2.2.1 and 5.3 . There are various methods in use. 2 For short stress histories where simple loading events are repeated a number of times, the Reservoir method is recommended. It is easy to visualise and simple to use see figure 4.5.1 . Where long stress histories have to be used, such as those...

Definitions

Miner Modified Fatigue Curve

1.5.1 Terms common to all Eurocodes 1 P Unless otherwise stated in Part 1 of Eurocode 9 the terminology used in International Standard ISO 8930 applies. 1.5.2 Special terms used in this Part 2 of Eurocode 9 1 P The following terms are used in Part 2 of Eurocode 9 w ith the following meanings - Fatigue Weakening of a structural part, through gradual crack propagation caused by repeated stress fluctuations. - Fatigue loading A set of typical load events described by the positions or movements of...

Prenorme Europeenne Europische Vornorm

Descriptors civil engineering, steel construction, aluminium, design, building codes, computation, mechanical strength This European Prestandard ENV was approved by CEN on 26 October 1997 as a prospective standard for provisional application. The period of validity of this ENV is limited initially to three years. After two years the members of CEN will be requested to submit their comments, particularly on the question whether the ENV can be converted into a European Standard. CEN members are...

Hot spot stresses

1 The hot spot stress approach is used mainly for joints in which the weld toe orientation is transverse to the fluctuating stress component, and the crack is assumed to grow from the weld toe. The approach is not suitable for joints in which the crack would grow from embedded defects or from the root of a fillet weld. Compared with the nominal stress approach, this approach is more suitable for use in the following cases a there is no clearly defined nominal stress due to complicated...

Applicability of Nominal Modified Nominal and Hot Spot Stresses Nominal stresses

Elastic Stress

1 P Nominal stresses shall be used directly for the assessment of initiation sites in simple members and joints where the following conditions apply a The details associated with the site are in reasonable agreement with the appropriate detail category requirements in Tables 5.1.1 to 5.1.5. b The detail category has been established by test in accordance with Annex C and where the results have been expressed in terms of the nominal stresses. c Gross geometrical effects such as those listed in...

Full scale testing

1 Full scale testing may be carried out under actual operating conditions, or in a testing facility with the test load components applied by hydraulic or other methods of control. 2 The conditions for manufacturing the structure should be as for component testing in C.3.1. 3 The loads applied should not exceed the nominal loads. 4 Where the service loads vary in a random manner between limits they should be represented by an equivalent series of loads agreed between the supplier and the...

Equivalent Fatigue Loading

1 P A simplified equivalent loading shall only be used in place of a more realistic fatigue loading if the following conditions are satisfied a The aluminium alloy structure shall fall within the range of basic structural forms and size for which the equivalent fatigue loading was originally derived. b The real loading shall be of similar intensity and frequency and be applied in a similar way to that assumed in the derivation of the equivalent fatigue loading. c The values of mi, m2, ND and...

Use of finite elements for fatigue analysis A Element types A Beam elements

1 Beam elements are mainly used for analysis of nominal stresses in frames and similar structures. A conventional beam element for analysis of three dimensional frames has 6 degrees of freedom at each end node three displacements and three rotations. This element can describe the torsional behaviour correctly only in cases in which the cross section is not prone to warp, or warping can occur freely. Analysis of warping stresses is impossible, when open thin-walled structures are analysed. 2...

Partial Safety Factors for Fatigue Loading

1 Where the fatigue loading has been derived in accordance with the requirements of 3.2 a partial safety factor on load intensity yFf i gjmay be assumed to provide an acceptable level of safety. 2 Where a fatigue loading has been based on other confidence limits than those in 3.2 4 , an acceptable level of safety may be assumed to be provided by applying the partial safety factors on loading in Table 3.4.1. Table 3.4.1 Partial safety factors for fatigue load intensity yFf Table 3.4.1 Partial...

Control of welding quality

Welding Discontinuity Image

1 The manufacturer shall conform with the quality requirements of EN 729-2. D.1.2.2 Welding co-ordination 1 The welding co-ordination personnel shall have comprehensive technical knowledge in accordance with EN 719. 1 Welding procedures shall be approved in accordance with EN 288-4. D.1.2.4 Welder approval 1 Welders shall be approved in accordance with EN 287-2. D.1.2.5 Welding processes 1 Control of welding shall be in accordance with EN 1011-1 and 4. D.1.3 Methods and extent of Inspection 1...

National foreword

This Draft for Development is the official English version of ENV 1999-2 1998. This publication is not to be regarded as a British Standard. It is being issued in the Draft for Development series of publications and is of a provisional nature. It should be applied on this provisional basis, so that information and experience of its practical application may be obtained. Comments arising from the use of this Draft for Development are requested so that UK experience can be reported to the...

Dressing by TIG or plasma

1 While TIG welding is only a practical process for structures made of plates 4mm thick or less, it can be used for improving the fatigue strength in cases where the weld toe is the critical site. When re-melting the existing toe region inclusions and undercuts can be removed and the toe radius can be increased which reduces the local stress concentration factor. 2 Standard TIG dressing equipment can be used, without the addition of any filler material. TIG dressing is sensitive to operator...