Crash and Safety

Highlights

Major improvements for airbags, in particular Starter capability to generate automatic Finite Volume Mesh for folded complex airbags to account for internal airbag topology: inter-chamber surfaces, retainers etc. Pre-simulation for airbag folding is becoming a standard, but having the folded bag respecting its package constraints requires additional morphing operations that are now implemented inside the solver.

Tied contact has an extended penalty formulation, to overcome issues with multiple incompatible kinematic conditions; main advantage versus previous formulation is the conservation of both forces and moments. There are no over-costs compared either to kinematic formulation or former penalty one.

Composites is another domain of major improvements. Ply based input, equivalent to OptiStruct input, is not only more intuitive, but allows seamless combined crash/impact and strength simulations, or multi-objective optimization. The coupling with MDS (Multiscale Design Systems) opens the door for material law identification as well design to answer specific dedicated behaviors.

Globally material laws and rupture criteria are fundamental issues for all the industries in the virtual testing approaches. A new material law for high strength steel with strain rate and temperature dependencies developed by MIT provides an accurate prediction of the local strain fields with a consistent damage indicator.

Damage is an important indicator for failure of components; stress and strain only are often not sufficient to estimate components failure, because failure in tension/compression/shear occurs at different stress and strain levels. Damage visualization, available for all failure criteria and both solids and shells, allows to have a more precise estimation about how close to failure are elements. It is also possible to initialize damage, for example to take into account damage due to forming process of a given component.

•	Destination Reference (Fitting): Technology to morph folded airbags into given its destination. Folded airbag mesh usually does not fit into its destination in packaging space; the airbag is gradually morphed into its destination by defining both the envelop surface and the destination surface.

•	Automatic FVM mesh for multi-chambered airbags: FVM mesh taking into account internal inter-chamber surfaces, retainer etc. is generated automatically by the Starter.

•	FVM solution speed: Improvement of the FVM method parallelization, offering nice scalability in SMP.

•	Airbag tethers: Advanced option in /PROP/TYPE4 (H1 = 8: elastic total length function) allowing to define the force as a function of total actual length, as opposite to the regular force as a function of elongation (H1 = 0).

•	Fabric material laws: Advanced fabric material LAW58 has an extended formulation describing with higher accuracy the mechanical behavior of fabric at high strain values; new transverse shear modulus Gsh between layer.

•	Pyramid element available for gas mesh: In case of manual mesh, element compatibility has been extended to pyramid elements.

•	Pyramid element available for internal FVM mesh.

•	FVM compatibility with /LEAK/MAT: Possibility to model leakage through porous fabric surfaces.

•	Reference state: /EREF compatibility with TETRA4 elements. /EREF is compatibility with /REFSTA and /XREF in case there are no common nodes between these 3 options to define a reference state.

•	//SUBMODEL: Compatibility extended to /MONVOL/COMMU1, /MONVOL/FVMBAG1, /LEAK, and /EREF.

•	Local parameters implemented for //SUBMODEL. This allows to parametrize airbag, seatbelt and other RADIOSS models.

•	New friction formulation with static force and dynamic coefficient input; it allows to better control relative motion. For example, tangential motion starts only if the tangential force exceeds the static friction force.

•	Damping coefficients are available for both normal and friction force as a function of relative velocity and of normal contact force.

•	New option Icor to adjust the contact force due to initial intersection.

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New penalty formulation (Spotflag=26) designed to overcome limitations of the existing one (Spotflag=25): not only forces but also moments are fully transmitted from master segment to slave node, respecting global balance. It is less sensitive to errors due projections outside the master segment; performance are similar to Spotflag=25.

•	Stiffness control for penalty formulation (Spotflag=25, 26): user can tune the penalty stiffness to prevent time-step drops, that might occur especially when the ratio slave/master stiffness is big.

•	Slave node projection control: to prevent negative mass errors, in case the slave node projection is close, but outside the master segment, the user can force slave projection on the edge of the master segment (Iproj=0, default in v14.0).

•	Error/Warning messages are compacted into the Starter output file, making it more readable and lighter in terms of file size. For example, instead of repeating the same error message for each node, a single error message is output with a list of the nodes.

•	Possibility to define default values of contact flags, by contact type. For example, stiffness flag, etc.

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Ply-based input: new input type for multi-layer composites based on plies. Plies are identified with groups of elements, which is closer to designers experience and manufacturing process. RADIOSS and OptiStruct ply-based input are now fully consistent, allowing easy conversion from one format into the other both ways, making combined crash/impact and strength simulations seamless, including optimization.

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QEPH shells compatibility with orthotropic properties/materials: QEPH is an under-integrated shell element with physical hourglass control; with a very small computational over-cost gives results with high accuracy, close to fully integrated elements which are traditionally used for composites. QEPH v. Batoz elements computation time can be estimated as a factor of 3.

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Sandwich shell (PID11): Global material properties are now automatically calculated based on the properties of the layup in membrane and bending
A material for part definition is still needed (for pre- and post-treatment purposes). The stability condition is recalculated and offset layup stability is improved; this may change results within the magnitude of the model numerical sensitivity. Global material properties are also used to compute time-step and contact stiffness.

MDS (Multiscale Design Systems): complete environment for analysis and design of heterogeneous material.

•	Direct coupling with RADIOSS through dll.

•	MDS can be used to identify the parameters of the RADIOSS laws for example law 25 for composite.

Metals:

•	/MAT/LAW84: Swift-Voce elastic-plastic law with Johnson-Cook strain rate hardening and temperature softening.

•	/MAT/LAW52 (GURSON): User-defined yield stress; input is yield stress table (yield stress v. plastic strain) activated with the new flag Iyield. Strain rate hardening is also possible. The regular Johnson-Cook parameters are used if table_ID=0.

•	/MAT/LAW2: Possible to input yield-stress, Ultimate engineering tensile stress or engineering strain at UTS with new flag “Iflag” in /MAT/LAW2.

Foams:

•	/MAT/LAW77: porous foam material law. This porous material law is compatible with moving structures.

Spotwelds:

•	/MAT/LAW59 and /MAT/LAW83: new flag Imass for mass calculation: spotweld mass can be computed either using the volume or the area (upper and lower average).

•	Physical thickness could be taken into account for moments computation (True thickness in /PROP/CONNECT).

•	/MAT/LAW59: The Starter checks and errors out if the slope of the input curve is higher than the Young's modulus.

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Spotwelds lines and clusters: /CLUSTER allows to group of elements with LAW59 or LAW83 material into a cluster of spotweld elements. Cluster allows to output summed force and moments acting to all elements of the cluster. Cluster failure criterion can be defined based in these forces and moments. Cluster can be used also with spring elements.

Polymers:

•	Elastic-plastic material with a non-linear elastic section for solid (LAW65 compatibility extended to all solid elements: hexa, tetra and thick-shells).

XFEM

•	Possibility to separate the crack initiation and advancement criteria extended to other compatible failure models (Dadv in /FAIL/TBUTCH and new function fct_IDadv in /FAIL/FLD).

•	No more number of layer limitation with X-FEM in /PROP/SH_SANDW (/PROP/TYPE11).

•	By making /MAT/HILL (LAW32) and /MAT/HILL_TAB (LAW43) compatible with /PROP/SH_SANDW (/PROP/TYPE11) X-FEM can be applied to orthotropic materials.

Thermal stress and expansion:

•	Generalized to all material laws (for both shell and solid elements).

Damage and Failure index:

•	Possibility to output damage and failure index for all failure criteria using /ANIM/SHELL/DAMA or /ANIM/BRICK/DAMA.

•	Hill’s law for muscles: /PROP/SPR_MUSCL is a spring property for modeling active/passive muscle behavior in crash events; it is an elastic-viscous plastic law with user-defined functions reflecting time dependent muscle behavior in tension (force v. deflection or force v. time).

•	Possibility to define edge to edge contact for XELEM: a part of XELEM can be set in /LINE/PART to define contacts with /INTER/TYPE11.

•	Improved hourglass control in HEPH element: Hourglass tangent modulus control (IHKT) extended to orthotropic properties (/PROP/TYPE6).

•	Improved energy computation for pre-tensioner spring: initial/added internal energy for /PROP/TYPE32 (SPR_PRE) to avoid negative energy.

Airbags:

•	Non-consistent temperature/fluid velocity output when automatic mesh is used (FVMBAG1).

•	Porosity curve shifted not respected if controlled by Ittf (=0, 1, or 2).

•	LAW58 nonlinear curve input not read correctly.

•	Starter issues Warning 941 (surface not closed) even when the airbag surface is closed.

•	FVM: general robustness improvements (better control on the evolution of the number of finite volumes).

•	/FVMBAG1 with tetra mesh and internal surfaces. Result of pressure in time history and animation does not match.

•	Error message is issued, if vent a hole in /FVMBAG1 is not determined through a physical components.

•	Added a warning for FVMBAG when a node belongs to several inflators.

•	Starter will issue a Warning (instead of an error), if a vent hole area is not defined for UP airbags.

•	Possible Starter segmentation violation error while try to write finite volumes in animation file (Ifvani=1 in /MONVOL/FVMBAG1).

•	/IMPDISP does not does not imposed nodes, if /IMPDISP/FGEO used.

•	Airbag internal surfaces is ignored by FVM.

Contact TYPE6:

•	Formulation flag not detected (Iform, nonlinear behavior with constant unloading stiffness).

Tied Contact TYPE2:

•	Possible segmentation violation when using interface TYPE2 in 2D analysis.

•	With ignore=2, Starter does not report a problem of non-projected node as expected.

•	With IGNORE >= 1, if slave nodes are not tied, warnings are compacted to improve readability.

Contacts:

•	TYPE7: Possible Engine failure if Irem_gap=2 with SPMD version is used.

•	TYPE7: The gap calculated by RADIOSS for Igap=3 does not match the theoretical value.

•	TYPE11: When contact is defined inside a submodel with different units, dtmin value is not scaled.

•	TYPE17: Hertz contact may not work if several interfaces TYPE17 are defined.

•	TYPE17: Contact might not be detected if the top face of SHELL16 is impacting the master SHELL16.

•	TYPE21: Possible segmentation error due to restart writing is wrong if using Interface type 21 + INACTI=6.

Composites:

•	/MAT/LAW25.

-	Wrong RADIOSS units for WPLAREF and WPLAMX: if Wp_ref=0, Wp_ref=1 will be considered whatever units system used which is not correct.

-	Possible engine segmentation violation error with solids and thick-shells.

-	Wrong strain tensor output in animation file for solids and thick-shells.

-	No element (with LAW25 CRASURV Formulation) deletion despite number of failed layer in animation.

•	Elements possible deletion during initialization of orthotropy directions with the /INISHEL_ORTHO_LOC card.

•	Failure appears too early with Puck criterion; failure might occur even if the failure is switched off (all strengths to 1e30).

•	Extended incompatibility checks with orthotropic law + isotropic property and print the warning message.

•	/PROP/SH_SANDW: Add error message if /PROP/SH_SANDW is used with incompatible material.

•	Unstable solution by use AMS + Ipos=1 in sandwich shell property and all the ply define on one side of the middle plane shell.

•	Starter error out and info incompatibility for orthotropic material laws(LAW43,73) with sandwich property.

•	Model with Idrill=1 + Batoz + Composites fails due to energy error limit reached.

Material and Failure Models:

•	LAW35: Issue due to wrong unit convert for LAW35 in /BEGIN.

•	LAW59: Possible wrong behavior of /FAIL/CONNECT on win64 (energy criterion is ignored).

•	LAW83: Plastic strain output is wrong (in both ANIM and TH).

•	LAW50: Strain rate not available and wrong Starter printout.

•	LAW66: Wrong elastic-plastic behavior for solid elements.

•	LAW70: Incorrect default Qa and Qb values in the Starter printout file.

•	LAW70: Wrong results in animation, if using LAW 70 and Ismstr=11/Iframe=2.

•	LAW42 and LAW65: Incorrect time-step estimation in the Starter.

•	/MAT/LAW44 (COWPER): Calculates the strain-rate effect even with C=0 (no strain rate effect).

•	/FAIL/LAD_DAMA input: Wrong order of Ifail_sh (shell) and Ifail_so (solid).

•	Possible segmentation violation Error when none plastic law (e.g. LAW42) with tensstrain failure criteria.

•	INICRACK (X-FEM) might delete instead of splitting elements.

•	LAW24: Dilatancy (s0/fc) default value, leads to NaN Error.

•	LAW24 is compatible with tetra10.

•	Different results between two unit systems used in a model with HEPH+IHKT=2+Hyperelastic laws (42, 62, 69, 82).

•	Use LAW42 with Prony coefficients showing unexpected zero reaction force at displacement=0 in the unloading cycle.

•	XFEM does not work correctly with multiple /FAIL/TAB1 cards (each of them with Ixfem = 1).

•	Corrected failure criterion (/FAIL/SNCONNECT) to match the theoretical results and also correct ANIM damage output in (/ANIM/BRICK/VDAM).

•	Possible segmentation violation error in engine for XFEM in win64 SMP.

•	No difference in results even with different input curves in /FAIL/ENERGY.

Properties:

•	When using 10 IPs over thickness, the structure shows strange stress output (waves) in animation files and in Time History file, as well. It does not happen, if using less than 10 IPs.

•	When solved using RADIOSS SPMD, NSTRAND/XELEM parts are missing from animation files and elements are incorrectly grouped.

•	Corrected curve description for PROP/SPRING in Starter output.

•	/PROP/KJOINT (TYPE33) does not work if both ends of the spring are without /RBODY.

•	In /PROP/KJOINT2 (TYPE45) friction force is incorrect in case SD+ and SD- are set to zero.

•	Deformation of solid connect element will not be stable when connected shell elements are deleted.

•	In /PROP/TYPE4 (SPRING) with H=7, the output force does not follow the prescribed force/displacement curve. And also fix the behavior for non-homogenous spring groups.

•	Correct negative internal energy when using Isolid=17+LAW34.

•	/PROP/TYPE22+LAW25: incorrect strain output for thick shell elements with Isolid=14.

•	Possible engine error(NaN in IE) due to Starter change Ismstr=1 is changed to Ismstr=11 with REFSTA + LAW36.

•	Correct shell stress results through the thickness when more than 1 IP defined through thickness.