{"id":32483,"date":"2019-01-07T20:58:27","date_gmt":"2019-01-07T20:58:27","guid":{"rendered":"\/forum\/forums\/topic\/calculating-alternating-strain-strain-amplitude-mean-strain\/"},"modified":"2019-01-07T20:58:27","modified_gmt":"2019-01-07T20:58:27","slug":"calculating-alternating-strain-strain-amplitude-mean-strain","status":"closed","type":"topic","link":"https:\/\/innovationspace.ansys.com\/forum\/forums\/topic\/calculating-alternating-strain-strain-amplitude-mean-strain\/","title":{"rendered":"Calculating alternating strain \/ strain amplitude \/ mean strain"},"content":{"rendered":"<p>Hey,<\/p>\n<p><\/p>\n<p>I am doing a static structural analysis with ANSYS Workbench R19.0. This analysis contains 2 load steps. In my opinion there are nodes which change from a (main) load under tension [load step 1] to a (main) load under pressure [load step 2]. <strong>How can I calcute the mean strain and the strain amplitude \/ alternating strain between these 2 load steps?<\/strong> Is there a way to get the results automatically or do I have to calculate it by myself?<\/p>\n<p><\/p>\n<p>It would be best to compare the resulting (alternating and mean) von Mises strains and principal strains. It is unknown whether the material can be described by von Mises strains or principal strains.<\/p>\n<p><\/p>\n<p>&#8212;<\/p>\n<p><\/p>\n<p>I tried the following approaches to calculate the strain amplitude for one examplary node. It would be nice to get feedback. I dont know whether I am totally wrong, but here are my thoughts:<\/p>\n<p><\/p>\n<ul><\/p>\n<li>First I compared the <strong>von Mises strain<\/strong> in both load steps for <strong>one examplary node<\/strong>: As the von Mises strain only calculates an absolute strain, tension and pressure can not be distinguished. The von Mises strain is not changing much between both load steps (equivalent von Mises strain load step1=5%, load step2=6,5%). This is clear as it is a matter of the formula to calculate the von Mises strain, but in my mind it pretends a strain amplitude (1,5%) which is too small (I calculated: strain amplitude = v.M. strain load step 1 &#8211; v.M. strain load step2).<\/li>\n<p><\/p>\n<li>Then I compared the <strong>principal strains in this exemplary node<\/strong>:\n<ul><\/p>\n<li>load step 1: epel1= 5%, epel2= 1%, epel3= -4%<\/li>\n<p><\/p>\n<li>load step 2: epel1= 4%, epel2= 0,5%, epel3= -7%<\/li>\n<p><\/p>\n<li>As you can see the highest absolute value changes from 5% (load step1, epel1) to -7% (load step2, epel3). In my mind this is an evidence that the load is changing from tension to pressure. I found 2 hypotheses to calculate the equivalent principal strain, but I am not sure about the english names, so I just describe the hypotheses:\n<ul><\/p>\n<li>if the material is critical to principal stresses and you want to calculate the equivalent strain:\n<ul><\/p>\n<li>principal strain hypothesis 1:<\/li>\n<p><\/p>\n<li>equivalent strain= 1\/(1+poissons ratio)*[<span class=\"st\">&epsilon;<\/span>1+poissons ratio\/(1-2*poissons ratio)*{<span class=\"st\">&epsilon;<\/span>1+<span class=\"st\">&epsilon;<\/span>2+<span class=\"st\">&epsilon;<\/span>3}]. I am not sure: is <span class=\"st\">&epsilon;1 the max strain (=4% in load step 2) or absolute max strain (= -7% in load step2). I think it should be -7 % if you look at a unidirectional case.<br \/><\/span><\/li>\n<p><\/p>\n<li>this would result in a equivalent strain(load step 1)= 8,56 % and a equivalent strain(load step 2)= -11,23% (alternatively -3,59 %). So I could calculate a strain amplitude of 8,56+11,23=19,79% (alternatively 8,56+3,59=12,18%). This sounds reasonable.<\/li>\n<p>\n<\/ul>\n<p>\n<\/li>\n<p><\/p>\n<li>if the material is critical to principal strains and you want to calculate the equivalent strain:&nbsp;&nbsp;\n<ul><\/p>\n<li>principal strain hypothesis 2:<\/li>\n<p><\/p>\n<li>equivalent strain= max(<span class=\"st\">&epsilon;<\/span>1, <span class=\"st\">&epsilon;<\/span>2, <span class=\"st\">&epsilon;<\/span>3)<\/li>\n<p><\/p>\n<li>this would result in a equivalent strain(load step 1)= 5 % and a equivalent strain(load step 2)= 4%. So I could calculate a strain amplitude of 5% &#8211; 4%= 1%. This sounds too small.<\/li>\n<p>\n<\/ul>\n<p>\n<\/li>\n<p>\n<\/ul>\n<p>\n<\/li>\n<p>\n<\/ul>\n<p>\n<\/li>\n<p>\n<\/ul>\n<p><\/p>\n<p>Thanks in advance! Why are the results so different? I am excited to get to know about your thoughts.<\/p>\n<p><\/p>\n<p>Regards,<\/p>\n<p><\/p>\n<p>maddes<\/p>\n","protected":false},"template":"","class_list":["post-32483","topic","type-topic","status-closed","hentry"],"aioseo_notices":[],"acf":[],"custom_fields":[{"0":{"_bbp_old_topic_id":["4655"],"_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":["2101"],"_bbp_subscription":["236846"],"_bbp_topic_status":["unanswered"],"_bbp_status":["publish"],"_bbp_topic_id":["32483"],"_bbp_forum_id":["27791"],"_bbp_engagement":["240","158256"],"_bbp_voice_count":["2"],"_bbp_reply_count":["3"],"_bbp_last_reply_id":["74488"],"_bbp_last_active_id":["74488"],"_bbp_last_active_time":["2019-01-10 21:16:02"]},"test":"maddes"}],"_links":{"self":[{"href":"https:\/\/innovationspace.ansys.com\/forum\/wp-json\/wp\/v2\/topics\/32483","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\/32483\/revisions"}],"wp:attachment":[{"href":"https:\/\/innovationspace.ansys.com\/forum\/wp-json\/wp\/v2\/media?parent=32483"}],"curies":[{"name":"wp","href":"https:\/\/api.w.org\/{rel}","templated":true}]}}