VIII-2 elastic-plastic sample stress strain data points for verification

[keyen]

Would anyone be willing to post your elastic-plastic stress-strain data points (per Annex 3-D) for a material such as SA-516 so that I can compare it to my MathCAD results?

thanks

 

[TGS4]

Sure. What temp? What are you using as your proportional limit?

 

[keyen]

Trevor, 100F would be fine. I'm using Ey=29.4E+06 psi.

 

[keyen]

Addendum: I'm using epsilon_ys=0.002 and epsilon_p=2.0e-5

 

[TGS4]

Stress   Plastic Strain
21000	 0
22000	 3.26E-05
23000	 4.55E-05
24000	 6.27E-05
25000	 8.53E-05
26000	 1.15E-04
27000	 1.52E-04
28000	 2.01E-04
29000	 2.62E-04
30000	 3.39E-04
31000	 4.35E-04
32000	 5.54E-04
33000	 7.02E-04
34000	 8.84E-04
35000	 1.11E-03
36000	 1.38E-03
37000	 1.72E-03
38000	 2.13E-03
39000	 2.63E-03
40000	 3.25E-03
41000	 4.00E-03
42000	 4.93E-03
43000	 6.06E-03
44000	 7.44E-03
45000	 9.11E-03
46000	 0.011122
47000	 0.013488
48000	 0.016213
49000	 0.019267
50000	 0.022585
51000	 0.026079
52000	 0.029658
53000	 0.033246
54000	 0.036795
55000	 0.04029
56000	 0.043738
57000	 0.047165
58000	 0.050602
59000	 0.054081
60000	 0.057633
61000	 0.061284
62000	 0.065053
63000	 0.068959
64000	 0.073016
65000	 0.077234
66000	 0.081622
67000	 0.086188
68000	 0.090939
69000	 0.09588
70000	 0.101017
71000	 0.106355
72000	 0.111898
73000	 0.117651
74000	 0.12362
75000	 0.129807
76000	 0.136219
77000	 0.14286
78000	 0.149734
79000	 0.156846
80000	 0.164202
81000	 0.171806
82000	 0.179663
83000	 0.187779
84000	 0.196157
85000	 0.204804
86000	 0.213725
87000	 0.222925
88000	 0.232409
89000	 0.242183
90000	 0.252252
91000	 0.262621
92000	 0.273296
92091.344 	0.274287

My calculation of the proportional limit is based on when the calculated plastic strain is greater than epsilon_p. Note that the FE software that I use requires that the plastic strain at the proportional limit be set equal to zero - hence the zero plastic strain in the first row.

 

[keyen]

TGS4: I was able to get the same results as you; however, we calculated plastic strain in a different manner.

I expected plastic strain = ε_t(σ) - ε_p. Whereas, you calculated plastic strain = ε_t(σ) - σ/E_y.

My version keeps the elastic strain constant (equal to ε_p); however your elastic strain continues past the proportional limit (as σ/E_y).

Is this a result of how your FE software expects the data; or am I misinterpreting something?

I've attached a screenshot of my data. Row "C" is my interpretation of the plastic strain; and row "D" is how I reverse engineered your interpretation (equal to your dataset posted previously).

thanks,
Dave

 

[TGS4]

Total strain is equal to the elastic strain plus the plastic strain. The elastic strain is σ/E. That is true regardless of whether you are above or below the proportional limit - there is always elastic strain. ε_p defines the proportional limit (which is different for different materials).

I'm not sure how you made your interpretation from Annex 3-D? Your interpretation is incorrect. Refer to equation 3-D.1. gamma_1 + gamma_2 IS the plastic strain, which when added to the elastic strain, gives you the total strain.

 

[keyen]

Trevor: thanks again for all the info. I don't know how you find the time. Do you ever sleep? As your were writing your last post, I re-read the definition of y_1 and y_2. They are of course, like you said, the plastic components of the total stain.

My incorrect interpretation was formed based on how I believed material behaves beyond the proportional limit. I did not think that additional elastic strain (equal to sigma/E) would form in the plastic region. I was under the assumption that elastic strain's upper bound was equal to the strain at the proportional limit.

 

[TGS4]

You're welcome. It's part of my job, actually. Plus, I know this stuff inside and out.

Have you considered taking a course on this topic (VIII-2 Part 5)?

 

[keyen]

TGS4: I took your course a few months back in Dallas. Most of my time is spent in Division 1, I'm just playing catch up on the details of Division 2 now.