{"id":41783,"date":"2020-03-13T23:15:55","date_gmt":"2020-03-13T23:15:55","guid":{"rendered":"\/forum\/forums\/topic\/static-structural-snap-deflection-analysis-strain-doesnt-correspond-to-stress\/"},"modified":"2020-03-13T23:15:55","modified_gmt":"2020-03-13T23:15:55","slug":"static-structural-snap-deflection-analysis-strain-doesnt-correspond-to-stress","status":"closed","type":"topic","link":"https:\/\/innovationspace.ansys.com\/forum\/forums\/topic\/static-structural-snap-deflection-analysis-strain-doesnt-correspond-to-stress\/","title":{"rendered":"Static structural\u2014Snap deflection analysis: Strain doesn’t correspond to stress?"},"content":{"rendered":"

Hello,<\/p>\n

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I ran a static structural analysis of a snap with multilinear kinematic hardening plasticity. The material at hand is a plastic resin with 30% glass fill—data sheet shows a break stress of 130MPa and a break strain of 2.5% (see engineering stress-strain curve below).<\/p>\n

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So, in my engineering data I have Isotropic Elasticity (E=9500MPa, v=0.35) plus Multilinear Kinematic Hardening (see graph below).<\/p>\n

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For the multilinear inputs, I made sure to transform the engineering stress-strain data given by supplier to true stress-strain data, followed by the plastic strain calculation. The model converged quickly and behaved as expected, but I got confused when checking the strain and stress results. When looking at the Max. Principal Strain, results show a max of ~1.4% of strain which is considerably below the 2.5% break strain of the material (according to engineering stress-strain curve). But when I look at the Max. Principal Stress, results show a max of ~133.3MPa which is a bit above the 130MPa break stress of the material (according to engineering stress-strain curve). <\/p>\n

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Why is there this discrepancy? I would think beforehand that the stress and strain results would correspond to the true stress-strain curve input (true s-s curve is very similar to engineering s-s curve anyhow). But it seems if I read strain results, I would approve this design since results are considerably below the break strain limit, whereas if I read stress results I wouldn’t approve this design as it’s marginal. If I read ~1.4% of strain I would expect to read ~110MPa in stress. What am I missing? I also checked Von-Mises and it’s the same story, although I think Max. Principal Stress failure theory applies more due to the high percentage of glass fibre in the resin.<\/p>\n

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Warm regards,<\/p>\n

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Richard<\/p>\n

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 <\/p>\n","protected":false},"template":"","class_list":["post-41783","topic","type-topic","status-closed","hentry"],"aioseo_notices":[],"acf":[],"custom_fields":[{"0":{"_bbp_old_topic_id":["13963"],"_bbp_old_topic_author_name_id":["Anonymous"],"_bbp_old_is_topic_anonymous_id":["false"],"_bbp_old_closed_status_id":["publish"],"_bbp_author_ip":[null],"_bbp_old_sticky_status_id":["normal"],"_bbp_likes_count":["0"],"_btv_view_count":["1841"],"_bbp_subscription":["248548"],"_bbp_topic_status":["unanswered"],"_bbp_status":["publish"],"_bbp_topic_id":["41783"],"_bbp_forum_id":["27791"],"_bbp_engagement":["240","174328","174682","262268"],"_bbp_voice_count":["4"],"_bbp_reply_count":["16"],"_bbp_last_reply_id":["110173"],"_bbp_last_active_id":["110173"],"_bbp_last_active_time":["2020-04-05 18:11:15"]},"test":"rgarcia60"}],"_links":{"self":[{"href":"https:\/\/innovationspace.ansys.com\/forum\/wp-json\/wp\/v2\/topics\/41783","targetHints":{"allow":["GET"]}}],"collection":[{"href":"https:\/\/innovationspace.ansys.com\/forum\/wp-json\/wp\/v2\/topics"}],"about":[{"href":"https:\/\/innovationspace.ansys.com\/forum\/wp-json\/wp\/v2\/types\/topic"}],"version-history":[{"count":0,"href":"https:\/\/innovationspace.ansys.com\/forum\/wp-json\/wp\/v2\/topics\/41783\/revisions"}],"wp:attachment":[{"href":"https:\/\/innovationspace.ansys.com\/forum\/wp-json\/wp\/v2\/media?parent=41783"}],"curies":[{"name":"wp","href":"https:\/\/api.w.org\/{rel}","templated":true}]}}