(1)P The generalised form of the AaN 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 AaN 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 nondamaging. 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 AaN 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 cutoff limit AaL, which occurs at 108 cycles, should be assumed to be nondamaging.
(6) The AaN 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 AaN 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 nondestructive 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).
(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 reentrant 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 
1217 
867 
967 
697 
967 
697 
867 
627 
776 
776  
Key: —» requirement continues from left to right 
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 19992:1998 Table 5.1.2(a) Members with Welded Attachments  Transverse Weld Toe
Number of cycles, N Fig. 5.2.2(a)AaN curves for members with welded attachments  transverse weld toe

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