## 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 detail; Aci s the principal stress range at the detail and is constant for all cycles; m} is the inverse slope of the Aa-N curve, depending on the detail category;

yFf is the partial safety factor allowing for uncertainties in loading spectrum and analysis of response (see 3.4); YMf is the partial safety factor for uncertainties in materials and execution (see 5.2.1(3)).

(3) For normal applications where the design conforms with this Prestandard, including the manufacturing requirements of Annex D, a value of yMf= 1,0 may applied (but see 5.2.3(3) in the case of adhesively bonded joints).

(4) The constant amplitude fatigue limit, AaD, occurs at 5x106 cycles, below which constant amplitude stress cycles are assumed to be non-damaging. However, even if occasional cycles occur above this level, they will cause propagation which, as the crack extends, will cause lower amplitude cycles to become damaging. For this reason the inverse logarithmic slope m2 of the basic Aa-N curves between 5 x 106 and 108 cycles should be changed to m2 for general spectrum loading conditions, where m2 = mi + 2.

(5)Any stress cycles below the cut-off limit AaL, which occurs at 108 cycles, should be assumed to be non-damaging.

(6) The Aa-N relationship is folly described by the double number detail categoiy Aac - mi where Aac is an integer expressed in units of N/mm2. Their values are given in tables 5.1.1 to 5.1.5. The Aa-N curves are given in figures 5.2.1 to 5.2.5.

(7) For the purpose of defining a finite range of categories and to enable a category to be increased or decreased by a constant geometric interval, a standard range of Aac values is given in table 5.2.6. An increase (or decrease) of 1 category means selecting the next larger (or smaller) Aac value whilst leaving mi and m2 unchanged.

8)P The detail categories are safe for all values of mean stress (see 5.3) but do not allow for environments other than ambient (see 5.4).

9) The use of the m2 = mi + 2 inverse slope constant may be conservative for some spectra. Where a design is critically dependent on this region and where maximum economy is sought it may be appropriate to consider using component testing (see Annex C.3.1) or applying fracture mechanics analysis (see Annex B).

(10)P The detail category values in tables 5.1.2(b) and 5.1.3 shown in brackets are attainable only with high weld quality levels which are not readily verifiable by normal non-destructive testing techniques. In order to meet the needs of quality assurance, bracketed values should only be used where special inspection procedures are applied which have been demonstrated to be capable of detecting and evaluating critical sizes of weld discontinuity which shall have been established by fracture mechanics or testing (see Annex B and C).

### 5.2.2 Unclassified details

(l)Details not fully covered by tables 5.1.1 to 5.1.5 should be assessed by reference to published data where available. Alternatively fatigue acceptance tests may be carried out in accordance with Annex C.3

(1) Design of adhesive joints should consider the following:

- Stress concentrations should be minimised.

- Strains in the parent metal should be kept below yield.

- Chemical conversion or anodizing of the surfaces generally improves fatigue life compared to degreasing or mechanical abrasion.

- Aggressive environments usually reduce fatigue life.

(2)The reference fatigue strength of an adhesively bonded lap joint which fails in the bond line is defined by the equation:

where kc,adh is the value of the adhesive joint fatigue strength factor kadh at N = 2x106 cycles fv,adh is the characteristic shear strength of the adhesive obtained from a standard static lap shear test (see Part

1.1 of this Prestandard).

(3)Testing under representative conditions of geometry, workmanship and environment is recommended for critical applications. Otherwise a high value of yMf should be used.

Table 5.1.1 Detail Categories for Plain Material

Extrusion direction

 Product Forms Sheet, Plate, Simple Extruded Rod and Bar Shaped Extrusions, Tubes, Forgings Sheet, Plate, Solid Extrusions, Forgings Hollow Extrusions Castings Initiation Site Reference No. 1,2 1,2 1,2 2 1 3 Location Small surface irregularity -> -> Extrusion seam Surface irregularity Internal discontinuity Stress orientation (see 4.3.4) PARALLEL to rolling or extrusion direction -> NORMAL to rolling >r extrusion direction NORMAL to extrusion direction - - Alloys 7020 astable 1.1.1 (except 7020) 7020 astable 1.1.1 (except 7020) 7020 astable 11.1 (except 7)20) 7020 6**** series astable 1.1.1 astable 1.1.2 Particular Requirements Dimensional Surfaces free of sharp corners unless parallel to stress direction —> -» -> No re-entrant corners in profile, No contact with other parts Fabrication Machining only by high speed milling cutter Hand grinding not permitted unless parallel to stress direction Extruded by port hole or bridge die Casting as per Table 1.1.2. Machining permitted if by high speed milling cutter. Inspection/Testing Visual -» —► -> —3 Drift tests at extrusion ends Dye Pen. Radiography Annex D table D.3 Quality Standard Surface finish (R,< 0.5mm) No score marks transverse to stress direction H No drift test fracture along weld seam Annex D table D.4 Stress Analysis Stress parameter Principal structural stress at initiation site -> -» - Stress concentrations already allowed for Surface texture -> -> —> -> Permitted internal porosity Type Number 1.1 1.2 1.3 1.4 1.5 1.6 1.7 1.8 1.9 1.10 Detail Category Aac - mi 121-7 86-7 96-7 69-7 96-7 69-7 86-7 62-7 77-6 77-6 Key: —» requirement continues from left to right
Number of cycles, N Fig. 5.2.1Ao-N curves for plain material
Table 5.2.1 Numerical values of Aa (N/mm2) for plain material

Detail Categoiy (N = 2 x 106)

N = 105

Nd = 5x106

NL=108

Actc

m,

Act

Actd

Actl

121

7

185,6

106,2

76,1

96

7

147,3

84,2

60,4

86

7

131,9

74,4

54,1

77

6

126,9

66,1

45,5

69

7

105,9

60,5

43,4

62

7

95,1

54,4

ENV 1999-2:1998

Table 5.1.2(a) Members with Welded Attachments - Transverse Weld Toe

 Product Forms Rolled, extruded and forged products Initiation site Reference No. 1 2 3 4 Location At transverse weld toe on stressed member -> At longitudinal weld end on surface away from edge —> -> —> At corner On edge In ground weld toe on edge Stress orientation (see 4.3.4) Normal to transverse weld toe -» -> —► —> Parallel to weld axis Alloys Astable 1.1.1. —> —» -> -> -> -» —► —► Particular Requirements Geometry Attachment on member surface —> -> —> —> Attachment on member edge Weld on surface away from comer -> Welded round corner Weld on edge Length L(mm) > £ 0 10 10 20 20 30 30 50 50 80 80 120 120 200 ¥ L and T as for Types 2.1 to 2.8 Radius Corner radius R (mm) Thickness T (mm) See table below —► —> —► 1(KR<20 2040 Fabrication Grind undercut smooth Grind radius in direction of Aa* Inspection/testing As Annex D table D1 —> -> —> —► —> —> -» Quality standard As Annex D table D2 —> —> —> —► —> —> Stress Analysis Stress Parameter Nominal stress at initiation site —> —> —► -> —► Stress concentrations already allowed for Weld profile permitted by Annex D Table D2 -> -> —> —» —► Stiffening effect of attachment -> —> —> —> -> Type Number 2.1 2.2 2.3 2.4 2.5 2.6 2.7 2.9 2.10 2.11 2.12 2.13 Detail Category Actc mi = 3,2 for all types T<4 440 31 31 31 31 31 31 28 28 28 28 28 28 25 25 25 25 25 25 25 22 22 22 22 22 25 22 20 20 20 20 25 22 20 18 18 18 16 14 As Types 2.1 to 2.8, but reduced by one Detail Category 18 25 28 31 Adjustment for stress gradient where Ao\ and A2 are of opposite sign increase by 2 Categories v here T<15mm or 1 Category where 15

Number of cycles, N

Fig. 5.2.2(a)Aa-N curves for members with welded attachments

- transverse weld toe

Table 5.2.2(a) Numerical values of Aa (N/mm2) for members with welded attachments - transverse weld toe

Detail Category (N = 2 x 106)

N= 10s

ND = 5xl06

NL=108

A CTC

mi

Act

Actd

Actl

31

3,2

79,1

23,2

13,1

28

3,2

71,4

21,0

11,8

25

3,2

63,8

18,8

10,6

22

3,2

56,1

16,5

9,3

20

3,2

51,0

15,0

8,4

18

3,2

45,9

13,5

7,6

16

3,2

40,8

12,0

6,8

14

3,2

35,7

10,5

ENV 1999-2:1998

Table 5.1.2(b) Detail Categories for Members with Welded Attachments - Longitudinal Welds

 Product Forms Rolled, extruded and forged products Initiation Site Reference No. 1 2 3 4 5 Location A weld discontinuity weld ripple Stop-start Weld toe or crater Weld toe or crater Stress orientation (see 4.) Parallel to weld axis —> -» —> —> Alloys As table 1.1.1. -> —> Particular Requirements Dimensional Full penetration Intermittent fillet weld Cope hole centred on weld axis Double sided butt weld G < 2.5L R < 25mm Manufacturing Continuous automatic welding Weld caps ground flush in direction of Ds Any backing bars (and attachment welds) to be continuous —> Inspection/Testing As Annex D Table D1 -> Quality Standard As Annex D Table D2 —> -> Stress Analysis Stress Parameters Nominal stress at initiation site —> -> -> Any attachment material to be included in section properties —> Stress concentrations already allowed for Weld discontinuities permitted by Annex D Table D. 1. -» -> presence of cope hole Type Number 2.14 2.15 2.16 2.17 2.18 Detail Category Aac-m! (60-4,5) 55-4,5 44-4,5 35-4 31-3,5 28-3,5 Key: -» requirement continuous from left to right ( ) Before using values in brackets see 5.2.1(10)

Number of cycles, N

Fig. 5.2.2(b) A a-N curves for members with welded attachments

- longitudinal welds

Table 5.2.2(b) Numerical values of Aa (N/mm2) for members with welded attachments - longitudinal welds

Table 5.2.2(b) Numerical values of Aa (N/mm2) for members with welded attachments - longitudinal welds

Detail Category (N = 2 x 106)

N= 105

ND = 5xl06

NL=108

Aac

m,

Ac

Actd

Actl

(60)

4,5

116,8

48,9

30,9

55

4,5

107,0

44,9

28,3

44

4,5

85,6

35,9

22,6

35

4

74,0

27,8

16,8

31

3,5

73,0

23,9

13,8

28

3,5

65,9

21,6

ENV 1999-2:1998

Table 5.1.3 Detail Categories for Welded Joints Between Members

 Product Forms Rolled, extruded and forged products -> —> Castings Initiation sites Reference No. 1,2 3,2 4 5 6 7 8 9,10 11 as Types 3.1 to 3.10 Locations surface or embedded discontinuity weld toe or embedded discontinuity weld root root discontinuity unfused root weld toe weld toe weld root weld toe weld root Stress orientation (see 4 ) Normal to weld axis -> ->• —► Alloys As tab 1.1.1 -> -> -> -> -> tab 1.1.2 Particular Dimensional Joint type In-line butt —► -> -> Cruciform or Tee Lap Requirements Weld type Butt -> —► —► —► Butt fillet Preparation Double sided —► Single sided -> Penetration Full -> partial full partial Transition Taper slope £1 in 4 at width or thickness change -> as Types 3 .1 to 3 .10 Manufacturing Root Ground Backed Unbacked Ground Cap Ground flush Ends Extension plates used on ends, cut off and ground flush in direction of Aa —» Inspection/Testing As Annex D Table D.l —► —► —> -> —» —> Quality Standard As Annex D Table D.2 —» -> Stress Analysis Stress parameter Net throat + specified misalignment stress (no overfill) —> net section net throat net section net throat Stress concentration effects included in Detail Category Profile, unspecified misalignment and discontinuties permitted by Annex D Table D.2 -> Stiffening effect of transverse element stress peaks at weld ends Type Number 3.1 3.2 3.3 3.4 3.5 3.6 3.7 3.8 3.9 3.10 3.11to3.20 Detail Category Actc - mi Flats, solid (55-6) 44-5 (39-4) 354 (35-4) 25-3,2 (29-3,2) 18-3,2 14-3,2 as Table 5.1.2(a) Types 2.1 to 2.9 3.7 14-3,2 as Types 3.1 to 3.10 less 1 Detail Category Open shapes (44-5) 28-4 (35-4) 28-4 Hollow NA NA Key: NA = not applicable, -» requirement continuous from left to right ( ) Before using values in brackets see 5.2.1(10)

Number of cycles, N Fig. 5.2.3 A a-N curves for welded joints between members

 Detail Category (N0 = 2 x 106) N= 105 ND = 5xl06 Nl=108 Aac mi Act Actd Actl (55) 6 90,6 47,2 32,5 44 5 80,1 36,6 23,9 39 4 82,5 31,0 18,8 35 4 74,0 27,8 16,8 28 4 59,2 22,3 13,5 25 3,2 63,8 18,8 10,6 18 3,2 45,9 13,5 7,6 14 3,2 35,7 10,5 5,9
Stress Range Aa, N/mm2

104 105 106 107 10® 109

Number of cycles, N

Fig. 5.2.4 A o-N curve for mechanically fastened joints

104 105 106 107 10® 109

Number of cycles, N

Fig. 5.2.4 A o-N curve for mechanically fastened joints

 Detail Category (N = 2 x 106) N= 105 ND = 5xl06 NL=108 A ac m, Aa Actd ACl 55 4 116.3 43.7 26.5

Table 5.1.5 Detail Category for Adhesively Bonded Joints

Table 5.1.5 Detail Category for Adhesively Bonded Joints

<-=--*

 Product Forms Rolled, extruded and forged products Initiation site Reference No. 1 Description In bond line at leading edge Stress orientation Normal to leading edge Alloys As table 1.1.1 Adhesives Single and two-part epoxies Particular Requirements Thickness of thinner part < 8mm Fabrication Machining only by high speed milling cutter Surface Preparation Degreasing or chromate conversion Assembly Bond line thickness within tolerances specified for shear strength test Inspection/Testing as Part 1-1 Stress Analysis Stress Parameter Average shear stress based on a effective length Ladh (see 4.4.3(11)) Stress concentrations already allowed for Stress peak at leading edge, eccentricity of load path in symmetrical double covered lap joints only Detail Category Aac - n\\ 0,11 fvadh " 6

Number of cycles, N

Number of cycles, N

 Detail Categoiy (N = 2 x 106) N= 105 ND = 5xl06 NL=108 AOc/fv,adh mi Aa/fvad), ACTo/fv,adh ACTL/fv,adh 0.11 6 0.181 0.94 0.065

Table 5.2.6. Standard range of Aoc values (N/mm2)

12,14, 16, 18,20,22,25,28,31,35,39,44,49, 55,62,69, 77, 86,96, 108,121,

Note: does not apply to adhesively bonded joints__

5.2.4 Hot spot stress

Values of A ac for hot spot stress assessment of weld toes are given in table 5.2.7.

 Thickness of stressed member T (mm) Actc- m. 0 40 25 -3,2