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

5.2.3 Adhesively bonded joints

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

- Peel loading should be reduced to a minimum.

- 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

20<R<40

R>40

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 4<T<10 1(KT<15 15<T^25 25<T<40 T>40

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<T<40mm

Key: * Weld toe shall be fully ground out -►requirement continuous from left to right

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

Table 5.23 Numerical values of Aa (N/mm2) 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

Fastener Type

Preloaded (Friction Type)

Non-Preloaded (Bearing Type)

High strength bolt

Tensioned Rivet

Bolt

Driven Rivet

Product Forms

Rolled, extruded and forged products

—>

—>

Initiation site

Reference no.

1,(2)

1.(2)

2

2

Location

In front of hole (sometimes at edge of hole)

—►

Edge of hole

—>

Stress orientation

Parallel to rolling or extrusion direction

—>

Alloys

As table 1.1.1

—►

—>

Fastener Materials

Steel, Rpo,23 640 N/mm2

As Part 1

Particular Requirements

Dimensional

Lap joint with flat parallel surfaces

—>

Lap joint

Steel washer under boit head and nut

Fabrication

Machining only by high speed milling cutter

Holes drilled (with optional reaming) or punched (with compulsory reaming if thickness >6mm)

—>

Assembly

Degreased or shot blast faying surfaces to be in full contact with 30% pre-load in all bolts

Degreased or shot blast faying surfaces to be in full contact using temporary bolts

Holes in plies to be aligned within ± 0.5mm

Fastening

Bolts to be torqued to minimum of 85% of proof load

Rivet head to be swaged whilst rivet under a minimum 85% proof load

Bolts to be torqued to minimum 50% proof load unless lock nuts used

Rivets driven until faying surfaces in contact

Inspection/Testing

Final torque/nut rotation checked after tightening complete

Final torque checked if lock nuts not used

Stress Analysis

Stress Parameter

Nominal stress based on GROSS section properties

Nominal stress based on NET section properties

Stress concentrations already allowed for

Surface texture, fastener hole geometry, unequal load distribution between rows of bolts, eccentricity of load path in SYMMETRICAL DOUBLE COVERED lap joints only

Type Number

4.1

4.2

4.3

4.4

Detail Category Aac - mi

55-4

55-4

55-4

55-4

Key requirement continues from left to right

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

Table 5.2.4. Numerical values for Aa (N/mm2) 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

Stress range ratio Aa/fV|adh

Stress range ratio Aa/fV|adh

Number of cycles, N

Number of cycles, N

Fig. 5.2.5 Aa/t,ad»rN curve for adhesively bonded joints

Table 5.2.5. Numerical values for kadh (=Aa/fv,adh) for adhesively bonded joints

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.

Table 5.2.7 Actc -mi values for hot spot stress assessment

Thickness of stressed member T (mm)

Actc- m.

0<T<4

44 -3,2

4 <T < 10

39 -3,2

10 <T ^ 15

35 -3,2

15 <T<25

31 -3,2

25<T<£40

28 -3,2

T> 40

25 -3,2

0 0

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