{"id":352335,"date":"2024-02-19T15:13:06","date_gmt":"2024-02-19T15:13:06","guid":{"rendered":"\/forum\/forums\/topic\/questions-on-explicit-dynamics-settings\/"},"modified":"2024-02-19T15:13:06","modified_gmt":"2024-02-19T15:13:06","slug":"questions-on-explicit-dynamics-settings","status":"closed","type":"topic","link":"https:\/\/innovationspace.ansys.com\/forum\/forums\/topic\/questions-on-explicit-dynamics-settings\/","title":{"rendered":"Questions on Explicit Dynamics Settings"},"content":{"rendered":"

Dear community,<\/p>\n

First of all, I am sorry in advance for the long post. I am new to Explicit Dynamics and I would like some input from you so I can understand how correct my model is set up.<\/p>\n

I am trying to analyze the impact of a rigid hollow cylinder against an Aluminum plate (Al 6061-T6, explicit materials library), using Autodyn. I went through most of the theory guide in the manual, but I am still not sure what are the best configurations for this type of analysis.<\/p>\n

<\/p>\n

The plate is fixed on the top and bottom edges, and the cylinder hits it with 72m\/s. No contacts are initially defined and body interaction settings is default (frictionless). The goal of my analysis is to define a minimum plate thickness to withstand the impact, and evaluate the force reaction to quantify the amount and size of screws that will be holding that plate.<\/p>\n

I have run 6 different calculation scenarios, changing some key settings between each. These settings are: including or not material failure model (max effective plastic strain), element erosion and viscous coefficient of hourglass forces (HVC). The mesh is really coarse, just so I could run this scenarios in a short time.<\/p>\n

The first two scenarios were without any material failure, just with different HVC values (0.1 and 0.05). Scenarios 3 and 4 include material failure at a defined max plastic strain (obtained from stress-strain curve). Finaly, the last two scenarios include both material failure + erosion (on material failure).<\/p>\n

Scenarios 1 and 2 (the most conservative and likely artificially stiff models) show the highest plastic strain (even higher than failure criteria, of course) and a (expected) reduction on hourglass energy when decreasing the HVC, which corresponds to 9.6% and 7.3% of the plate internal energy. It also shows the highest reaction force.<\/p>\n

3 and 4 (failure on plastic strain, no erosion) result in a “cap” of plastic strain based on the value I input as failure, a sligthly higher internal energy and a stable ratio of 10.5% hourglass energy contribution, even when changing the HVC.<\/p>\n

5 and 6 (failure + erosion) also cap the plastic strain, and show a huge decrease in the internal energy of the plate due to element erosion. From the around 600 J of the first four scenarios, it went to 500 J (HVC=0.1) and down to 400 J (HVC=0.05), bringing the hourglass ratio to 13% and 18%, respectively.<\/p>\n

The reaction forces were also decreasing as I made the model “softer”, from 670 kN in scenarios 1 and 2, to 550 kN in scenario 6.<\/p>\n

Ok, now to the questions:<\/p>\n

    \n
  1. I have a strain-stress curve from uniaxial test data, showing fracture on a plastic strain of 13%. I am using 11% as failure limit for the simulations. Does it even make sense to use data from such a simple test in a dynamic model?<\/li>\n
  2. Does it make sense to use this failure criteria in a model dominated by compression stress?<\/li>\n
  3. When I leave failure ON but erosion OFF, the failed elements behave very weirdly after impact (see picture below). Why is that?<\/li>\n
  4. Reducing the HVC value from scenario 3 to 4 did not improved the ratio between hourglass and internal energies. Why is that?<\/li>\n
  5. I understand that erosion is a numerical approach to keep the time step reasonable. I can also see it clearly influencing the physics of my simulation in scenario 6, where, due to erosion, it seems like the cylinder has two impacts against the plate. Is there a clever way to use this feature in this type of simulation, or should I simply turn it off for good?<\/li>\n
  6. Which scenario would you consider a valid one?<\/li>\n<\/ol>\n

    I left below some graphs comparing these scenarios, and I hope it helps to better understand.<\/p>\n

    <\/p>\n

    Picture of the weird elements after failing:<\/p>\n

    <\/p>\n

    Sorry once again for the long post, thanks in advance for whoever find the time to answer, and I am looking forward this discussion!<\/p>\n

    Best regards,
    Henrique<\/p>\n","protected":false},"template":"","class_list":["post-352335","topic","type-topic","status-closed","hentry","topic-tag-ansys-autodyn-1","topic-tag-erosion-1","topic-tag-FailureModel-1","topic-tag-hourglass-energy","topic-tag-impact-analysis"],"aioseo_notices":[],"acf":[],"custom_fields":[{"0":{"_bbp_subscription":["254589","13468"],"_bbp_author_ip":["23.206.193.154"]," _bbp_last_reply_id":["0"]," _bbp_likes_count":["0"],"_btv_view_count":["2882"],"_bbp_topic_status":["unanswered"],"_bbp_topic_id":["352335"],"_bbp_forum_id":["27814"],"_bbp_engagement":["13468","254589"],"_bbp_voice_count":["2"],"_bbp_reply_count":["3"],"_bbp_last_reply_id":["353484"],"_bbp_last_active_id":["353484"],"_bbp_last_active_time":["2024-02-23 13:39:15"]},"test":"henrique-geraissatedesy-de"}],"_links":{"self":[{"href":"https:\/\/innovationspace.ansys.com\/forum\/wp-json\/wp\/v2\/topics\/352335","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\/352335\/revisions"}],"wp:attachment":[{"href":"https:\/\/innovationspace.ansys.com\/forum\/wp-json\/wp\/v2\/media?parent=352335"}],"curies":[{"name":"wp","href":"https:\/\/api.w.org\/{rel}","templated":true}]}}