Case 3: Indicate fatigue safety zone and plastic safety zone under 3 different conditions.
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Step 1: The fatigue safety zone is the area below the line connecting A' and E' and above the line connecting E' and the point where the line intersects the x-axis. Show more…
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Two main concepts do exist to analyse the safety of a structure with a resistance R and a solicitation S. • The safety margin M = R – S for which one has to check that M remains positive. • The global safety coefficient F = R/S for which one has to check that F is greater than 1. Let us analyse a square column of 25 cm edge, A being the cross-section. The compressive strength Rc is random and follows a normal distribution with mRc as the mean value and CVRc the covariance. The normal force N applied to the column follows the same distribution with mN as the mean value and CVN the covariance. One must check that N ≤ A.Rc, i.e. F = (A.Rc)/N ≥ 1. Numerical values: External force: mN = 1.5 MN and CVN = 30% Material strength: mRc = 30 MPa, CVRc = 20% Questions: 1. Compute the mean (deterministic) value of F and M based on the force as a function of the problem parameters. 2. Is it enough to estimate the safety of the column? Justify your answer. 3. Compute the distribution characteristics (mean value and variance) of the safety margin distribution. 4. Deduce the failure probability and compare the structural safety with respect to safety factor indicator.
Sri K.
Given a 1030 CR steel, estimate: a) the rotating-beam endurance limit at 10^6 cycles. b) the endurance strength of a polished rotating-beam specimen corresponding to 20,000 cycles to failure. c) the expected life of a polished rotating-beam specimen under a completely reversed stress of 75 kpsi.
Madhur L.
Figure 2 shows S-N curves for two types of materials A and B. Describe: a) The characteristic of fatigue behavior in material A and the example of material which experiences this type of fatigue behavior. b) The definition of endurance limit Se in material A. c) The characteristic of fatigue behavior in material B and the example of materials which experience this type of fatigue behavior. d) The definition of Fatigue Strength for material B. e) The definition of Fatigue Life for material B.
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