ME5513 :Fracture and Fatigue of Materials - Engineering Assignment Help

Assignment Task:

Task:

1. For double-edge-notched plate samples of 7075-T6 aluminum (figure below) under axial load, cycles to failure data are given below for various combinations of maximum stress Smax and mean stress Sm. The specimen dimensions were w1=38.10, w2=57.15, notch radius ρ=1.45, and thickness t=2.29 (all dimensions are in mm), giving kt=4.00 on the basis of net area. Also, the material’s tensile properties were yield strength of 521 MPa and ultimate strength of 572 MPa.

(i) Based on the date given in the table below, plot normalized amplitude-mean diagram, and then linear fit the data, then determine the ultimate tensile strength of the material, and compared with the value of 572 MPa given.
(ii) Fitting the data of zero mean stress to determine the constants A and B for S-N curve.
(iii) Using the Goodman relationship, plot Sar versus Nf for all of the data, also plot the zero-mean-stress fitted line (determined in
(ii)), and discuss the results of correlation.
(iv) Repeat (ii) using SWT relationship.
(v) Fitting these data to the Walker equation, all together as a single set of data to obtain values of A, B, and γ. Also, on a plot of Sar versus Nf, show data and fitted line.

Discuss the results of fitting (i) – (v).

3. A rod with changed section (Figure a), made of AISI4142 steel (σu=1757 MPa) and with dimensions of d1=15, d2=18, and ρ=1mm, is subjected to the axial load history shown in Figure b. Assume that the S-N curve can be expressed as following equation:
SSaaaa = 22222222NNff

−00.111111 MMMMMM

In the expected service of this component, 100 repetitions of the load history are anticipated.
(a) Estimate the number of repetitions that can be applied before fatigue failure occurs.
(b) What are the safety factors in life and in stress?

4. (a) A bending member has a rectangular cross section of dimensions of total width b=60 and thickness t=12 (all in mm). It is made of the AISI 4340 steel and is subjected to cyclic moment between Mmin = 0.8 and Mmax=4.0 kN.m. Failure occurred after 60,000 cycles of this loading by brittle fracture from a through thickness edge crack extension. Estimate the initial crack length present at the beginning of the cyclic loading.

(b) For the same material as in the part (a), if the initial crack length is ai = 0.5 mm, and the loading history is replaced by repeated applications of the sequence shown below, estimate the number of the repetitions to failure.
(Given materials constants as following: KIC = 130 MPam1/2, C0 = 5.11x10-10 (mm/cycle)/(MPam1/2)m, m=3.24, γ=0.42, and σys = 1255 MPa)

5. Plate with a round hole of 2024-T351 aluminum is axially loaded and have a static stress concentration factor of kt=2.4. Make estimations of
the life to fatigue cracking, and also plot the estimated stress-strain response, for cycling at R=0 with (a) Smax = 240 MPa, and (b) Smax = 345
MPa, using Morrow equation and SWT equation respectively. [For this material, E=73.1 GPa, H’=662 MPa, n’=0.070, σf’=927 MPa, b=- 0.113, εf’=0.409, c=-0.713].

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