Question

during a high cycle fatigue test, a metallic specimen is subjected to cyclic loading with a mean stress of 140 mpa and a minimum stress of -70 mpa. the r-ratio (minimum stress to maximum stress) for the cyclic loading is

Answer 1

The R-ratio, which is the ratio of minimum stress to maximum stress for the cyclic loading of the metallic specimen, is -0.2, indicating a cyclic loading that includes both tensile and compressive stresses.

Step-by-step explanation:

The question involves the concept of fatigue in materials engineering, specifically high cycle fatigue testing of a metallic specimen. In fatigue testing, a material is subjected to cyclic loading to understand how it behaves under repeated stress which can lead to failure even if the stress levels are below the material's yield strength.

The R-ratio is defined as the ratio of minimum stress to maximum stress in a cyclic loading scenario. Given that the mean stress is 140 MPa and the minimum stress is -70 MPa, we can deduce the maximum stress using the relation between mean stress (σ_m), maximum stress (σ_max), and minimum stress (σ_min):

σ_m = (σ_max + σ_min) / 2

Substituting the known values:

140 MPa = (σ_max - 70 MPa) / 2

σ_max = 350 MPa

Thus, the R-ratio is:

R = σ_min / σ_max

R = (-70 MPa) / 350 MPa

R = -0.2

The negative sign indicates that the cyclic loading includes both tensile and compressive stresses, as is common in fatigue testing scenarios.