Correlation b/w Fatigue Properties and Mechanical Properties 1

[MGMech]

Hi,

Fatigue life of parts are important for me. However, I can not make fatigue tests for all variations. I need to eliminate some variations before fatigue tests by evaluating mechanical properties or microstructure. I cannot find academic research to reference. I will be happy if I can have any support.
Materials and processes to evaluate;
1. High Strength Low Alloy Steels (4140, 4130, 4340)
2. Boron Steels (26MnB6, 30MnB5). Heat treated at different temperatures between 800 C and 925 C.
3. Weldment of Boront Steel

 

[metengr]

Find yourself a good engineering university library and start looking for fatigue curves on the mentioned steels for comparison and additional background on the response of high strength steel to cyclic loading.

 

[MGMech]

Hi,
Apart from fatigue life of base materials, I need total fatigue life welded assembly. This information cannot be found at databases. That's why I need to make tests. Results depend on base materials heat treated condition and welding parameters. It is obvious that there will be many variations and making fatigue tests for all is not simple. For this reason I'm looking for correlation information between simple statical mechanical test and fatigue information.

 

[metengr]

There are various international standards that provide suitable knock down factors for specific weld joint geometries (full penetration, partial penetration and fillet welds). In lieu of trying to calculate or determine the affects of welding on the fatigue life of specific steel (based on strength level from heat treatment), you should be researching knock down factors to compensate for the reduction in fatigue life from welding based on a known weld joint geometry.

 

[MGMech]

Could you recommend any standard regarding this subject? It would help me very much.
Thanks

 

[metengr]

http://www.researchgate.net/publication/244975265_Fatigue_design_rules_for_welded_structures

 

[MGMech]

There are some papers, I requested for full text. However these are not standards. After reading article I can evaluate if it can be referenced or not.

 

[metengr]

https://app.aws.org/wj/supplement/WJ_1972_11_s544.pdf

 

[TVP]

MGMech,

4130, 4140, 4340, 26MnB6, and 30MnB5 can all be quenched and tempered to the same hardness and strength levels, and thus have essentially the same fatigue strength. Alternatively, 4140 and 4340 can be hardened to deeper depths, due to the higher C concentration and alloying content. 4140 and 4340 can also be hardened to higher overall hardness than 4130, 26MnB6, or 30MnB5 due to the higher nominal C concentration, and thus have higher fatigue strength (high cycle fatigue). If the production quantities are low, then 4130, 4140, and 4340 are widely available, and easy to through harden. For higher production quantities, 26MnB6 and 30MnB5 offer the possibility for lower cost while achieving similar hardness/strength as the more expensive alloys. Shot peening is a low cost process that has significant effects on fatigue life of springs and sway bars (anti-roll bars), and allows lower cost steels to be used.

 

[Guest102023]

As an initial rough approximation, the fatigue strength of a ferritic steel is half the ultimate tensile strength, so that enables you to rank your candidates. This assumes all other factors are equal (e.g. surface finish, stress concentration factor, peening, etc.) The fatigue mechanism doesn't care too much what the composition and microstructure are.

Nitpick: be careful describing 4140, 4130, 4340 as 'High Strength Low Alloy Steels'. Yes they are 'high strength' and 'low alloy', but High Strength Low Alloy (HSLA) describes an entirely different class of steels.

"If you don't have time to do the job right the first time, when are you going to find time to repair it?"