Fatigue Calculators

Fatigue Calculation of a Welded Structures

This calculation determines the cyclic strength of welded structures. The calculation is performed for the most common types of welded joints and product loading conditions.

To perform calculations, the maximum σ_max and minimum σ_min tensile (compressive) cyclic stresses, as well as the material category should be specified.

The calculation of the number of allowable loading cycles has been performed in two ways, namely, N_crack according to the limit state criterion (formation of a fatigue crack 2-3 mm deep) and N_stress according to the maximum allowable stresses.

The fatigue strength of welded joint σ_R and cycle asymmetry coefficient R_σ are also calculated.

INITIAL DATA

σ_max - Maximum tensile (compressive) stress of loading cycle;

σ_min - Minimum tensile (compressive) stress of loading cycle.

RESULTS DATA

R_σ - Cycle asymmetry coefficient;

σ_R - Fatigue strength;

N_crack - Number of loading cycles to fatigue crack formation;

N_stress - Number of loading cycles according to the criterion of permissible stresses.

Metric Imperial

Maximum stress (σ_max)

Minimum stress (σ_min)

Low carbon steel

Low alloy steel

High strength steel

Cycle asymmetry coefficient (R_σ)

Fatigue strength (σ_R)

Number of cycles (N_crack)

Number of cycles (N_stress)

BASIC FORMULAS

Calculation performed for most common types of welds.

Cycle asymmetry coefficient:

R_σ = σ_max / σ_min;

Number of loading cycles N_stress:

σ_max = σ_R*e ^{A / [N_stress + B]};

σ_R - fatigue strength, determined from diagrams;

A, B - coefficients, depending on the ratio of σ_max / σ_min;

Number of loading cycles N_crack:

σ_max^m*N_crack = σ_R^m*N_G;

N_G = 2*10⁶ - base number of cycles to failure;

Exponent m is defined through parameters A, B, σ_R.

INITIAL DATA

σ_max - Maximum tensile (compressive) stress of loading cycle;

σ_min - Minimum tensile (compressive) stress of loading cycle.

RESULTS DATA

R_σ - Cycle asymmetry coefficient;

σ_R - Fatigue strength;

N_crack - Number of loading cycles to fatigue crack formation;

N_stress - Number of loading cycles according to the criterion of permissible stresses.

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