Card Variable MID EXCL MXPRES MNEPS EFFEPS VOLEPS NUMFIP NCS. Type A8 F F F F F F F. Default none none

Transcription

1 *MAT_A_EROSION *MAT *MAT_A_EROSION Many o the constitutive models in LS-YNA do not allow ailure and erosion The A_EROSION otion rovides a way o including ailure in these models although the otion can also be alied to constitutive models with other ailure/erosion criterion Each o the criterion deined here are alied indeendently, and once any one o them is satisied, the element is deleted rom the calculation NOTE: In the R4 release o 971, this otion alies to nonlinear element ormulations including the 2 continuum, 3 solid elements, 3 shell elements, and the thick shell elements tyes 1 and 2 In addition to erosion, damage initiation and evolution models are available as described in the remarks Card Variable MI EXCL MXPRES MNEPS EFFEPS VOLEPS NUMFIP NCS Tye A8 F F F F F F F eault none none Card Variable MNPRES SIGP1 SIGVM MXEPS EPSSH SIGTH IMPULSE FAILTM Tye F F F F F F F F eault none none none none none none none none The ollowing card is otional: Card Variable IAM MGTYP LCSG ECRIT MGEXP CRIT FAEXP LCREG Tye A8 F F F F F F F eault LS-YNA Version (MAT)

2 *MAT *MAT_A_EROSION I IAMGT0 deine the ollowing card: Card Variable SIZFLG REFSZ NAHSV LCSRS SHRF BIAXF Tye F F F F F F eault I IAMLT0 then deine -IAM set o cards on the ollowing ormat: Card Variable ITYP P1 P2 Tye F F F eault Card Variable ETYP CTYP Q1 Tye F F F eault VARIABLE MI ESCRIPTION Material identiication or which this erosion deinition alies A unique number or label not exceeding 8 characters must be seciied 1-16 (MAT) LS-YNA Version 971

3 *MAT_A_EROSION *MAT VARIABLE ESCRIPTION EXCL The exclusion number, which alies to the values deined on Card 2 When any o the ailure constants are set to the exclusion number, the associated ailure criteria calculations are byassed (which reduces the cost o the ailure model) For examle, to revent a material rom going into tension, the user should seciy an unusual value or the exclusion number, eg, 1234, set P min to 00 and all the remaining constants to 1234 The deault value is 00, which eliminates all criteria rom consideration that have their constants set to 00 or let blank in the inut ile MXPRES MNEPS EFFEPS Maximum ressure at ailure, P I the value is exactly zero, it is automatically excluded to maintain comatibility with old inut iles Minimum rincial strain at ailure, min I the value is exactly zero, it is automatically excluded to maintain comatibility with old inut iles dev dev Maximum eective strain at ailure, e 2/3ij ij I the value is exactly zero, it is automatically excluded to maintain comatibility with old inut iles I the value is negative, then EFFEPS is the eective lastic strain to ailure VOLEPS Volumetric strain at ailure, vol VOLEPS can be a ositive or negative number deending on whether the ailure is in tension or comression, resectively I the value is exactly zero, it is automatically excluded to maintain comatibility with old inut iles NUMFIP NCS MNPRES Number o ailed integration oints rior to element deletion The deault is unity LT00: NUMFIP is ercentage o integration oints/layers which must ail beore element ails (only GISSMO) Number o ailure conditions to satisy beore ailure occurs For examle, i SIGP1 and SIGVM are deined and i NCS=2, both ailure criteria must be met beore element deletion can occur The deault is set to unity Minimum ressure at ailure, P min SIGP1 Princial stress at ailure, SIGVM Equivalent stress at ailure, LS-YNA Version (MAT)

4 *MAT *MAT_A_EROSION VARIABLE MXEPS EPSSH ESCRIPTION Maximum rincial strain at ailure, The imum rincial strain at ailure is made a unction o the eective strain rate by setting MXEPS to the negative o the aroriate load curve I Shear strain at ailure, SIGTH Threshold stress, 0 IMPULSE Stress imulse or ailure, K FAILTM IAM MGTYP LCSG ECRIT MGEXP Failure time When the roblem time exceeds the ailure time, the material is removed Flag or damage model EQ0: no damage model is used EQ1: GISSMO damage model LT0: -IAM reresents the number o damage initiation and evolution criteria to be alied For GISSMO damage tye the ollowing alies EQ0: amage is accumulated, no couling to low stress, no ailure EQ1: amage is accumulated, element ailure occurs or =1 Couling o damage to low stress deending on arameters, see remarks below For IAMLT0 the ollowing alies EQ0: No action is taken EQ1: amage history is initiated based on values o initial lastic strains and initial strain tensor, this is to be used in multistage analyses Load curve I or Table I Load curve deines equivalent lastic strain to ailure vs triaxiality Table deines or each Lode angle value (between -1 and 1) a load curve I giving the equivalent lastic strain to ailure vs triaxiality or that Lode angle value Critical lastic strain (material instability), see below LT00: ECRIT is load curve I deining critical equivalent lastic strain vs triaxiality EQ00: Fixed value CRIT deining critical damage is read (see below) GT00: Fixed value or stress-state indeendent critical equivalent lastic strain Exonent or nonlinear damage accumulation, see remarks 1-18 (MAT) LS-YNA Version 971

5 *MAT_A_EROSION *MAT VARIABLE CRIT FAEXP LCREG SIZFLG REFSZ NAHSV LCSRS SHRF BIAXF ITYP ESCRIPTION amage threshold value (critical damage) I a Load curve o critical lastic strain or ixed value is given by ECRIT, inut is ignored Exonent or damage-related stress adeout LT00: FAEXP is load curve I deining element-size deendent ading exonent GT00: Constant ading exonent Load curve I deining element size deendent regularization actors or equivalent lastic strain to ailure Flag or method o element size determination EQ0 (deault): Element size is determined in undeormed coniguration as square root o element area (shells), or cubic root o element volume (solids), resectively EQ1: Element size is udated every time ste, and determined as mean edge length (This otion was added to ensure comarability with *MAT_120, and is not recommended or general urose) Reerence element size, or which an additional outut o damage will be generated This is necessary to ensure the alicability o resulting damage quantities when transerred to dierent mesh sizes Number o history variables rom damage model which should be stored in standard material history array or Postrocessing See remarks Load curve I deining ailure strain scaling actor vs strain rate GT0: scale ECRIT, too LT0: do not scale ECRIT Reduction actor or regularization at triaxiality=0 (shear) Reduction actor or regularization at triaxiality=2/3 (biaxial) amage initiation tye EQ00: uctile EQ10: Shear EQ20: MSFL LS-YNA Version (MAT)

6 *MAT *MAT_A_EROSION VARIABLE P1 P2 ETYP CTYP Q1 ESCRIPTION amage initiation arameter ITYPEQ00: Load curve/table I reresenting lastic strain at onset o damage as unction o stress triaxiality and otionally lastic strain rate ITYPEQ10: Load curve/table I reresenting lastic strain at onset o damage as unction o shear inluence and otionally lastic strain rate ITYPEQ20: Load curve/table I reresenting lastic strain at onset o damage as unction o ratio o rincial lastic strain rates and otionally lastic strain rate amage initiation arameter ITYPEQ00: Not used ITYPEQ10: Pressure inluence coeicient k S ITYPEQ20: Not used amage evolution tye EQ00: Linear amage comosition otion or multile criteria EQ00: Maximum EQ10: Multilicative amage evolution arameter ETYPEQ00: Plastic dislacement at ailure The criteria or ailure besides ailure time are: 1 P P, where P is the ressure (ositive in comression), and P imum ressure at ailure is the 2 3 min, where 3 is the minimum rincial strain, and min rincial strain at ailure is the minimum 3 P Pmin, where P is the ressure (ositive in comression), and P min minimum ressure at ailure is the 4 1, where 1 is the imum rincial stress, and is the imum rincial stress at ailure 5 3 ' ' 2 ij ij, where equivalent stress at ailure ' ij are the deviatoric stress comonents, and is the 1-20 (MAT) LS-YNA Version 971

7 *MAT_A_EROSION 6 1, where 1 is the imum rincial strain, and rincial strain at ailure *MAT is the imum 7 1, where 1 is the imum shear strain = ( 1 3 )/ 2 shear strain at ailure, and is the 8 The Tuler-Butcher criterion, t 2 [(0, 0 1 0)] dt K, where 1 is the imum rincial stress, 0 is a seciied threshold stress, 1 0 0, and K is the stress imulse or ailure Stress values below the threshold value are too low to cause racture even or very long duration loadings Remarks on amage Models: GISSMO The GISSMO damage model is a henomenological ormulation that allows or an incremental descrition o damage accumulation, including sotening and ailure It is intended to rovide a imum in variability or the descrition o damage or a variety o metallic materials (eg t o arameters is based on tabulated data, allowing the user to directly convert test data to numerical inut The model is based on an incremental ormulation o damage accumulation: 1 1 MGEXP MGEXP with : amage value 0 1 For numerical reasons, is initialized to a value o 1E-20 or all damage tyes in the irst time ste : Equivalent lastic strain to ailure, determined rom LCSG as a unction o the current triaxiality value : Equivalent lastic strain increment For constant values o ailure strain, this damage rate can be integrated to get a relation o damage and actual equivalent lastic strain: MGEXP or const only! LS-YNA Version (MAT)

8 *MAT *MAT_A_EROSION Triaxiality as a measure o the current stress state is deined as H with hydrostatic stress H M and equivalent von Mises stress M For MGTYPEQ0, damage is accumulated according to the descrition above, yet no sotening and ailure is taken into account Thus, arameters ECRIT, CRIT and FAEXP will not have any inluence This otion can be used to calculate re-damage in multi-stage deormations without inluencing the simulation results For MGTYPEQ1, elements will be deleted i eending on the set o arameters given by ECRIT (or CRIT) and FAEXP, a Lemaitre-tye couling o damage and stress (eective stress concet) can be used Three rincial ways o damage deinition can be used: 1) Inut o a ixed value o critical lastic strain (ECRITGT0) As soon as the magnitude o lastic strain reaches this value, the current damage arameter is stored as critical damage CRIT and the damage couling lag is set to unity, in order to acilitate an identiication o critical elements in ostrocessing From this oint on, damage is couled to the stress tensor using the ollowing relation: FAEXP CRIT 1 1 CRIT 1 This leads to a continuous reduction o stress, u to the load-bearing caacity comletely vanishing as reaches unity The ading exonent FAEXP can be deined element size deendent, to allow or the consideration o an element-size deendent amount o energy to be dissiated during element ade-out 2) Inut o a load curve deining critical lastic strain vs triaxiality (ECRITLT0), ointing to load curve I ECRIT This allows or a deinition o triaxiality-deendent material instability, which takes account o that instability and localization will occur deending on the actual load case This oers the ossibility to use a transormed Forming Limit iagram as an inut or the exected onset o sotening and localization Using this load curve, the instability measure F is accumulated using the ollowing relation, which is similar to the accumulation o damage excet or the instability curve is used as an inut: loc, 1 1 MGEXP MGEXP F F with F:,loc : Equivalent lastic strain to instability, determined rom ECRIT : Equivalent lastic strain increment 1-22 (MAT) LS-YNA Version 971

9 *MAT_A_EROSION *MAT As soon as the instability measure F reaches unity, the current value o damage in the resective element is stored amage will rom this oint on be couled to the low stress using the relation described above 3) I no inut or ECRIT is made, arameter CRIT will be considered Couling o amage to the stress tensor starts i this value (damage threshold) is exceeded damage to stress is done using the relation described above This inut allows or the use o extreme values also or examle, CRITEQ00 would lead to no couling at all, and element deletion under ull load (brittle racture) History Variables: History variables o the GISSMO damage model are written to the ostrocessing database only i NAHSV>0 The damage history variables start at osition N, which is dislayed in d3hs Variable escrition N amage arameter (1E-20 1) N+1 amage threshold CRIT N+2 omain lag or damage couling: =0 no couling =1 couling N+3 Triaxiality variable / N+4 N+5 N+6 N+7 N+8 N+9 N+10 N+11 N+12 H M Equivalent lastic strain Regularization actor or ailure strain (determined rom LCREG) Exonent or stress ading FAEXP Calculated element size Instability measure F Resultant damage arameter or element size REFSZ Resultant damage threshold CRIT or element size REFSZ Averaged triaxiality Lode angle value N+13 Alternative damage value: 1/ MGEXP amage initiation and evolution criteria As an alternative to GISSMO, the user may invoke an arbitrary number o damage initiation and evolution criteria, the number o course in ractice being limited by the number o available criteria With this otion the ollowing theory alies LS-YNA Version (MAT)

10 *MAT *MAT_A_EROSION Assuming that n initiation/evolution tyes have been deined according to the inormation above, i n being the same as IAM above, damage initiation and evolution history variables 0, i and 0,1, are introduced or each integration oint These are initially set to zero and then evolve with the deormation o the elements according to rules associated with the seciic damage initiation and evolution tye chosen, see below or details The variables can be ost-rocessed just as ordinary material history variables and their ositions in the history variables array is given in d3hs, search or the string amage history listing The damage initiation variables do not inluence the results but just serve as an indicator or the onset o damage The damage evolution variables govern the damage in the material and are used to orm the global damage 0,1 When multile criteria are active, n>1, each individual criterion can be o imum, i I, or multilicative, i Imult, tye, this is deined by the CTYP arameter The global damage variable is deined as where (, ) mult mult ii i 1 (1 ) iimult i The damage variable relates the macroscoic (damaged) and microscoic (true) stress according to (1 ) Once the damage has reached the level o erode (=099 by deault) the stress is set to zero and the integration oint is assumed ailed, thus not rocessed ater that When NUMFIP integration oints have ailed the element is eroded and removed rom the inite element model Now to the evolution o the individual damage initiation and evolution history variables, and or the sake o clarity we ski the suerscrit i rom now on The variables governs the onset o damage and evolves indeendently o each other and according to the ollowing uctile (ITYPEQ0): For the ductile initiation otion a unction (, ) reresents the lastic strain at onset o damage (P1) This is a unction o stress triaxiality deined as / q with being the ressure and q the von Mises equivalent stress Otionally this can be deined as a table with the second deendency being on the eective lastic strain rate The damage initiation history variable evolves according to 1-24 (MAT) LS-YNA Version 971

11 *MAT_A_EROSION *MAT 0 d Shear (ITYPEQ1): For the shear initiation otion a unction (, ) reresents the lastic strain at onset o damage (P1) This is a unction o a shear stress unction deined as ( qk )/ S with being the ressure, q the von Mises equivalent stress and the imum shear stress deined as a unction o the rincial stress values major minor /2 Introduced here is also the ressure inluence arameter k S (P2) Otionally this can be deined as a table with the second deendency being on the eective lastic strain rate The damage initiation history variable evolves according to 0 d MSFL (ITYPEQ2): For the MSFL initiation otion a unction (, ) reresents the lastic strain at onset o damage (P1) This is a unction o the ratio o rincial lastic strain rates deined as / minor / major The MSFL criterion is only relevant or shells and the rincial strains should be interreted as the in-lane rincial strains For simlicity the lastic strain evolution in this ormula is assumed to stem rom an associated von Mises low rule and whence s / s minor major with s being the deviatoric stress This assures that the calculation o is in a sense robust at the exense o being slightly o or materials with anisotroic yield unctions and/or non-associated low rules Otionally this can be deined as a table with the second deendency being on the eective lastic strain rate, or 0 the value o is set to a large number to revent onset o damage or no lastic evolution The damage initiation history variable evolves according to LS-YNA Version (MAT)

12 *MAT *MAT_A_EROSION tt, which should be interreted as the imum value u to this oint in time An imortant note with this initiation otion is that the damage initiation variable is evaluated using the strains and stresses at the mid-surace o the shell and thus bending eects are not taken into account For the evolution o the associated damage variable we introduce the lastic dislacement which evolves according to P u u 0 1 l 1 with l being a characteristic length o the element The ollowing deines the evolution o the damage variable Linear (ETYPEQ0): With this otion the damage variable evolves linearly with the lastic dislacement with u / u / u being the lastic dislacement at ailure (Q1) 1-26 (MAT) LS-YNA Version 971