{"id":28306,"date":"2017-10-30T00:48:25","date_gmt":"2017-10-30T00:48:25","guid":{"rendered":"\/forum\/forums\/topic\/multilinear-kinematic-plasticity-created-from-a-stress-strain-graph\/"},"modified":"2017-10-30T00:48:25","modified_gmt":"2017-10-30T00:48:25","slug":"multilinear-kinematic-plasticity-created-from-a-stress-strain-graph","status":"closed","type":"topic","link":"https:\/\/innovationspace.ansys.com\/forum\/forums\/topic\/multilinear-kinematic-plasticity-created-from-a-stress-strain-graph\/","title":{"rendered":"Multilinear Kinematic Plasticity created from a stress-strain graph"},"content":{"rendered":"<p>I was sent a stress-strain graph of a&nbsp;brittle metal&nbsp;tested in an Instron machine. It looked like this.<\/p>\n<p><\/p>\n<p><img decoding=\"async\" src=\"https:\/\/us.v-cdn.net\/6032193\/uploads\/attachments\/3e825b35-df61-45f5-9693-a81101684b62\/ae84f15c-bb1b-4731-9231-a81c000a3f26_plasticity-1.jpg?width=690&amp;upscale=false\" alt=\"\"><\/p>\n<p><\/p>\n<p>I have matlab and downloaded Grabit, a utility that makes digitizing data from a graph very easy. Here is what that looked like:<\/p>\n<p><\/p>\n<p><img decoding=\"async\" src=\"https:\/\/us.v-cdn.net\/6032193\/uploads\/attachments\/3e825b35-df61-45f5-9693-a81101684b62\/57adcf9f-b4ff-4e5d-91b8-a81c000aa873_plasticity-2.jpg?width=690&amp;upscale=false\" alt=\"\"><\/p>\n<p><\/p>\n<p>Now that I had the curve digitized, I could convert the Stress and Strain into True Stress and Plastic Strain so I could enter values in a material model using Multilinear Kinematic Plasticity. The formulas to convert are shown below:<\/p>\n<p><\/p>\n<p>E = 13,000 ksi<\/p>\n<p><\/p>\n<p>True Strain = ln(1+Strain)&nbsp; &nbsp;where ln is the natural logarithm function.<\/p>\n<p><\/p>\n<p>True Stress = Stress(1+Strain)<\/p>\n<p><\/p>\n<p>Elastic Strain = True Stress\/E<\/p>\n<p><\/p>\n<p>Plastic Strain = True Strain &#8211; Elastic Strain<\/p>\n<p><\/p>\n<p>I used a spreadsheet to correct the offset in the origin of the graph to put it back on zero.<\/p>\n<p><\/p>\n<p><img decoding=\"async\" src=\"https:\/\/us.v-cdn.net\/6032193\/uploads\/attachments\/3e825b35-df61-45f5-9693-a81101684b62\/eda14b0c-541b-42d8-90dd-a81c000cc9c7_plasticity-4.jpg?width=690&amp;upscale=false\" alt=\"\"><\/p>\n<p><\/p>\n<p>The first two columns came from the matlab Grabit utility.<\/p>\n<p><\/p>\n<p>The last two columns are copy paste into the Multlinear Plasticity material model, except for the first line.<\/p>\n<p><\/p>\n<p>The first first line is the yield stress. This was the material model used for the<a href=\"\/thread\/accurate-method-for-simulating-strain-in-fastener-threads\/\"> thread fracture analysis.<\/a><\/p>\n<p><\/p>\n<p>&nbsp;<\/p>\n","protected":false},"template":"","class_list":["post-28306","topic","type-topic","status-closed","hentry"],"aioseo_notices":[],"acf":[],"custom_fields":[{"0":{"_bbp_old_topic_id":["472"],"_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","0","0","0","0"],"_btv_view_count":["4417"],"_bbp_topic_status":["unanswered"],"_bbp_status":["publish"],"_bbp_topic_id":["28306"],"_bbp_forum_id":["27791"],"_bbp_engagement":["240","897","156165","158009","162031","163218","168667","176491","177582","177694"],"_bbp_voice_count":["10"],"_bbp_reply_count":["41"],"_bbp_last_reply_id":["150681"],"_bbp_last_active_id":["150681"],"_bbp_last_active_time":["2021-04-25 23:04:27"]},"test":"peteroznewman"}],"_links":{"self":[{"href":"https:\/\/innovationspace.ansys.com\/forum\/wp-json\/wp\/v2\/topics\/28306","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\/28306\/revisions"}],"wp:attachment":[{"href":"https:\/\/innovationspace.ansys.com\/forum\/wp-json\/wp\/v2\/media?parent=28306"}],"curies":[{"name":"wp","href":"https:\/\/api.w.org\/{rel}","templated":true}]}}