experimental strain-stress data of Neoprene rubber

[waterlilly]

hello, everyone,
i am a new-comer here. I have a silly question,
on material data link, how can a rubber material have a true strain less than or equal to -1? a true strain of -1, does it literally mean the thickness disappeared to zero, that is not possible, so, is it something related to volume change?

since i am new, am i entitled to 2 questions?
my second question is, neoprene material, after some process or coating, its tensile strength can be increased to 28 MPa, as compared to about 2MPa as specified on the experimental data here.
so, i will not be able to use the experimental stress-strain data provided here, right? i suppose they will be totally different materials then.

and please answer my first question. I am comfused.How can true strain be possibly below -1?

:wink: Happy Easter,

[CF]

To answer your first question:

True strain is defined as Ln( Length_final / Length_original)

From that definition, true strain can be less than -1.

You are perhaps confusing true strain with engineering or nominal strain.

[Jorgen]

Since CF already answered your first question, I'll address your second. Neoprene rubber is a class of materials that include both soft rubbers with low strength and stiffness and highly filled stiff materials with high strength. It is very possible that the material that you are interested in is quite different than the material that is presented in the experimental data section of this site.

- Jorgen

[wshrr]

can any body help me more in this same question.

can you for example show me how to convert from true to nom. stress or strain.please any help is appreciate it.you can use the neoprene_rubber data in this web.i used the eq.

True Strain = ln(1-nom.strn) ,even it is writtrn ln(1+nom.strn) in ABAQUS manual.

so, nom.strn=e^(True Strain), now if i applied this to the table in this web for neoprene_rubber ,i get nom srtn as follow:

1.0000
0.9843
0.9784
0.9722
0.9660
0.9599
0.9539
0.9477
0.9416
0.9357
0.9296
0.9238
0.9121
0.9062
0.9005
0.8947
0.8889
0.8833
0.8776
0.8720
0.8663
0.8609
0.8553
0.8498
0.8444
0.8390
0.8336
0.8282
0.8230
0.8177
0.8124
0.8073
0.8020
0.7968
0.7917
0.7867
0.7766
0.7717
0.7667
0.7619
0.7570
0.7522
0.7474
0.7427
0.7379
0.7332
0.7285
0.7238
0.7191
0.7145
0.7100
0.7054
0.7009
0.6965
0.6919
0.6875
0.6830
0.6788
0.6744
0.6700
0.6615
0.6572
0.6529
0.6488
0.6446
0.6405
0.6365
0.6324
0.6284
0.6243
0.6204
0.6164
0.6125
0.6085
0.6047
0.6009
0.5969
0.5931
0.5893
0.5856
0.5818
0.5780
0.5744
0.5706
0.5633
0.5598
0.5562
0.5526
0.5491
0.5456
0.5421
0.5386
0.5353
0.5318
0.5285
0.5250
0.5216
0.5184
0.5150
0.5117
0.5083
0.5051
0.5019
0.4987
0.4955
0.4924
0.4891
0.4860
0.4798
0.4767
0.4737
0.4706
0.4676
0.4645
0.4616
0.4587
0.4559
0.4538
0.4521
0.4511
0.4508
0.4515
0.4528
0.4547
0.4571
0.4600
0.4630
0.4659
0.4690
0.4720
0.4750
0.4781
0.4843
0.4874
0.4906
0.4938
0.4969
0.5001
0.5034
0.5066
0.5099
0.5131
0.5165
0.5198
0.5231
0.5266
0.5299
0.5333
0.5367
0.5402
0.5436
0.5472
0.5506
0.5542
0.5578
0.5613
0.5686
0.5723
0.5759
0.5797
0.5834
0.5871
0.5910
0.5948
0.5987
0.6025
0.6063
0.6103
0.6142
0.6182
0.6221
0.6261
0.6301
0.6342
0.6382
0.6424
0.6466
0.6506
0.6549
0.6591
0.6676
0.6719
0.6763
0.6806
0.6850
0.6895
0.6940
0.6984
0.7029
0.7075
0.7120
0.7166
0.7212
0.7259
0.7305
0.7353
0.7401
0.7448
0.7495
0.7543
0.7592
0.7640
0.7690
0.7738
0.7840
0.7889
0.7941
0.7992
0.8044
0.8095
0.8147
0.8200
0.8252
0.8306
0.8360
0.8415
0.8467
0.8522
0.8578
0.8632
0.8688
0.8744
0.8801
0.8857
0.8915
0.8973
0.9029
0.9088
0.9204
0.9263
0.9323
0.9382
0.9443
0.9505
0.9565

ARE VALUES COORECT OR NOT?.IF NOT CAN YOU SHOW ME THE CORRECT ONE.

[Jorgen]

True strain and nominal strain are related by the following equations:

strain_true = ln ( 1 + strain_eng )

strain_eng = exp( strain_true ) - 1

Note also that these equations are only valid when the material is incompressible, which is approximately true for all elastomers.

- Jorgen