{"id":249420,"date":"2023-02-10T15:43:46","date_gmt":"2023-02-10T15:43:46","guid":{"rendered":"\/forum\/?post_type=topic&p=249420"},"modified":"2023-02-10T15:43:46","modified_gmt":"2023-02-10T15:43:46","slug":"disparities-in-peak-stress-uniaxial-vs-flexural-loading-conditions","status":"closed","type":"topic","link":"https:\/\/innovationspace.ansys.com\/forum\/forums\/topic\/disparities-in-peak-stress-uniaxial-vs-flexural-loading-conditions\/","title":{"rendered":"Disparities in Peak stress \u2013 Uniaxial vs Flexural loading conditions"},"content":{"rendered":"

Hello, I was able to define non-linear material properties for concrete using APDL commands provided by Professor Brock D. Hedegaard as a base in Ansys Mechanical. The parameters are for a “Drucker-Prager Microplane plasticity ” model and attached below is the code:<\/p>\n

\/PREP7<\/div>\n
 <\/div>\n
! Step 1: Define elastic properties of material<\/div>\n
E = 30000           ! Young’s Modulus, MPa<\/div>\n
nu = 0.2            ! Poisson’s Ratio, unitless<\/div>\n
 <\/div>\n
! Step 2: Define microplane model properties <\/div>\n
!  – Approximations and typical ranges per intuition… your concrete may be different!<\/div>\n
fc = 80            ! Uniaxial compressive strength, MPa<\/div>\n
fb = 92             ! Biaxial compressive strength, MPa         (estimate as 1.15*fc if unknown)<\/div>\n
ft = 2            ! Tensile strength, MPa                     (estimate as 0.1*fc if unknown)<\/div>\n
Rt = 1              ! Tension cap hardening constant, unitless  (typically = 1)<\/div>\n
D = 20e4            ! Compressive hardening constant, MPa^2     (typically between 1e4 and 50e4)<\/div>\n
sigma_cv = -32      ! Int. of comp. cap and DP yield, MPa       (always negative, approximately -2\/3*fb or lower)<\/div>\n
Rc = 2              ! Compression cap ratio constant, unitless  (typically = 2)<\/div>\n
gamma_t = 0         ! Tensile damage threshhold, unitless       (typically = 0)<\/div>\n
gamma_c = 5e-5      ! Compressive damage threshhold, unitless   (typically between 1e-5 to 10e-5)<\/div>\n
beta_t = 6000       ! Tension damage evolution, unitless        (typically 1.5*beta_c)<\/div>\n
beta_c = 4000       ! Compression damage evolution, unitless    (typically between 1000 and 10000)<\/div>\n
 <\/div>\n
! Step 3: Define nonlocal parameters c and m<\/div>\n
c = 650             ! Nonlocal range parameter, mm^2            (element size should be < 0.5*sqrt(c))<\/div>\n
m = 2               ! Over-nonlocal parameter, unitless         (typically 1 to 3)<\/div>\n
 <\/div>\n
! Step 4: Select element type<\/div>\n
element = 215       ! Element type number (Linear = 215, Quadratic = 216)<\/div>\n
 <\/div>\n
 <\/div>\n
! ===================================================================<\/div>\n
! You should not need to change code below this point, unless<\/div>\n
! you are debugging, modifying, or otherwise know what you are doing<\/div>\n
! ===================================================================<\/div>\n
 <\/div>\n
! Assign Elastic Properties <\/div>\n
MP,EX,conc,E       ! Assign Young’s Modulus<\/div>\n
MP,NUXY,conc,nu    ! Assign Poisson’s Ratio<\/div>\n
 <\/div>\n
! Assign microplane properties for coupled damaged-plasticity (MPLANE-DPC)<\/div>\n
TB,MPLANE,conc,,,DPC<\/div>\n
TBDATA,1,fc,fb,ft,Rt,D,sigma_cv<\/div>\n
TBDATA,7,Rc,gamma_t,gamma_c,beta_t,beta_c<\/div>\n
 <\/div>\n
! Assign nonlocal properties to microplane model (MPLANE-NLOCAL)<\/div>\n
TB,MPLANE,conc,,,NLOCAL<\/div>\n
TBDATA,1,c,m<\/div>\n
 <\/div>\n
! Define coupled elements (this code assumes ITYPE = matid, which it should be in almost all cases)<\/div>\n
itype = conc<\/div>\n
 <\/div>\n
et,itype,element<\/div>\n
keyopt,itype,18,2     ! Element needs 2 nonlocal parameters for keyopt(18) <\/div>\n
 <\/div>\n
! Switch element type of those that are assigned Concrete<\/div>\n
esel,s,mat,,conc<\/div>\n
emodif,all,type,itype<\/div>\n
 <\/div>\n
! To check that everything worked out, print the element list<\/div>\n
allsel<\/div>\n
etlist,all<\/div>\n
 <\/div>\n
! Now proceed to the solution and output all results<\/div>\n
\/SOLU<\/div>\n
outres,all,all<\/div>\n
 <\/div>\n
 <\/div>\n
-Trying to validate the defined parameters, I modelled a generic beam and subjected it to uniaxial and flexural deflection schemes.<\/div>\n
The uniaxial loading conditions gave the expected results, with both compressive and tensile stress values peaking at the defined strength parameters before softening occurred. I have attached images below:<\/div>\n
 <\/div>\n
<\/div>\n

Fig.1 Peak compression<\/p>\n

<\/p>\n

Fig.2 Peak tension<\/p>\n

 <\/p>\n

-In contrast, flexural loading conditions give results for peak normal stress which significantly exceed defined parameters, even after varying the applied displacement on the beam.<\/p>\n

 <\/p>\n

<\/p>\n

Fig .3 Peak compressive and tensile stresses for the flexural loading condition.<\/p>\n

It is my understanding that the normal stress in the z-direction is composed of Tensile and compressive stresses beneath and above the neutral axis respectively. I would appreciate feedback on possible errors in my assumptions or potential reasons for the disparities in results.<\/p>\n

Thanks in Advance. <\/p>\n","protected":false},"template":"","class_list":["post-249420","topic","type-topic","status-closed","hentry","topic-tag-mechanicalworkbench-1","topic-tag-microplane-model","topic-tag-softening"],"aioseo_notices":[],"acf":[],"custom_fields":[{"0":{"_bbp_author_ip":["23.44.170.21"],"_bbp_subscription":["274845","88"],"_btv_view_count":["773"],"_bbp_likes_count":["1"],"_bbp_topic_status":["unanswered"],"_bbp_status":["publish"],"_bbp_topic_id":["249420"],"_bbp_forum_id":["27791"],"_bbp_engagement":["88","274845"],"_bbp_voice_count":["2"],"_bbp_reply_count":["3"],"_bbp_last_reply_id":["250270"],"_bbp_last_active_id":["250270"],"_bbp_last_active_time":["2023-02-16 19:55:03"]},"test":"b1254905live-tees-ac-uk"}],"_links":{"self":[{"href":"https:\/\/innovationspace.ansys.com\/forum\/wp-json\/wp\/v2\/topics\/249420","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\/249420\/revisions"}],"wp:attachment":[{"href":"https:\/\/innovationspace.ansys.com\/forum\/wp-json\/wp\/v2\/media?parent=249420"}],"curies":[{"name":"wp","href":"https:\/\/api.w.org\/{rel}","templated":true}]}}