Built-In Library of Methods

By default, HyperMesh comes with a set of methods. These methods are always available even if you register your own custom methods.

Restriction: There are limitations on supported result types for out-of-the-box methods provided in the installation:
  • Rivet: JointLoad: Only supported for op2 and xdb
  • Panel Metallic: Panel_FailureMode, Panel_ShearBuckling: Only supported for op2 and xdb
  • Panel Composite: First Ply Failure: Supported for op2, h3d and xdb
  • Beam: Stringer Axial Stress, Stringer Buckling, Stringer Axial Stress FBD, Stringer Buckling FBD: Only supported for op2 and xdb

JointLoad Method

The Rivet config is shipped with an internal method called JointLoad. This method extracts rivet forces/fluxes and moments on each and every layer (pierced shell) of a Rivet and populates a table with all extracted data.
Note: It does not compute any margin of safety and hence cannot be contoured.

You can chain another method which leverage data extracted from JointLoad to calculate a margin of safety.

On each pierced shell, the shell’s material system is extracted and a square box is created (so called extraction area) to compute fluxes and moments.The size of the box is driven by:
  • Rivet Diameter (held by the structural property)
  • Material scale factor
    • Metallic_D_scale: default to 4.0
    • Composite_D_scale: default to 4.5
    • User-defined scale factor (size_scale): default to 2.5

Box length=0.4*Size_scale*(D_scale*Diameter)



Figure 1.


Figure 2. Review extraction areas per plate
The method has some parameters used for load extraction:
BoxAngle
Tilt the box counterclockwise by this angle about pierced shell material Z axis.
Composite_D_scale, Metallic_D_scale, size_scale
Used to define box length.
IntPointSizePerEdge
Defines the number of integration points along each box edge.
  • First point on (-0.5;-0.5)*length
  • Default to 3 points per edge
  • Points are location where 2D element forces are interpolated
  • If results have no corner data, interpolation is done on nodal averaged forces
  • Interpolated forces on points are then averaged per side to compute Total/bypass fluxes
Tension_shell_material_system
  • 0: Rivet Max tension is extracted from raw 1D axial force Fx (default)
  • 1: Rivet Max tension is extracted from Z component in shell’s material system
There might be differences between the two options if 1D elements are not exactly perpendicular to pierced shell. The difference can be large if shear forces are huge compared to axial force due to projection in the shell’s material system.
DLS_calculations
  • 1: compute DLS Ratios
  • 0: do not evaluate DLS Ratios

First Ply Failure Method

The Panel_composite config comes with a set of various composite laminates first ply failure criteria. All of these failure criteria are bundled in a single certification method called “First_Ply_Failure”. This method internally invokes former ESACOMP engine.

Despite the method being available under the Panel_composite config, it evaluates failure criteria per element basis. As mentioned before, if the structural property assigned to a given designpoint refers to a user-defined property (PCOMP or PCOMPG), then all attributes required by the method are queried from this property. Otherwise, it will go directly per element’s property (supports PCOMP, PCOMPG, PCOMPP properties and MAT1, MAT8 cards).

All composite stresses are recalculated from shell element forces and moments based on the reference laminate property used. It then requires that result files contain shell element resultant forces and moments.

Math

Shell element resultant forces and moments (F/M/Q) are read from the result file and translated to the material orientation system based on the model. The moment sign conversion follows the notation used in [1]. Resultant forces and moments are translated to the geometrical mid-plane of the laminate. For ply-based models, local zone-laminates are automatically created. Strains and stresses are resolved at the three recovery planes of each layer using the Classical Lamination Theory. Out-of-plane shear stresses are determined based on [2] when needed. First ply failure-based analysis is performed for the selected design criteria and material combinations with single or multiple loadcases. For the required strength allowable, refer to the table below.


Figure 3. Required allowable per criteria

+ Max stress for isotropic material requires Xt, Xc and S and considers out-of-plane shear.

HM metadata values
  • R= Transverse_Shear_Allowable_S13
  • Q= Transverse_Shear_Allowable_S23
  • *E3

The bolded design criteria automatically considers out-of-plane shear stresses.

If R and Q (for MAT8) are defined, traditional in-plane criteria will also consider the out-of-plane shear.

Terminology

Reserve Factor is a measure of margin to the onset of failure. The effective load multiplied with the Reserve Factor gives the design margin. Thus, Reserve Factor values greater than one indicate a positive design margin and values less than one indicate a negative design margin. The values of Reserve Factors are always greater than zero. The term Factor of Safety is used with the Reserve Factor/Inverse Reserve Factor/Failure Index; this is determined as inv(Reserve Factor).

For linear criteria (max strain, max stress and max fiber stress), it is equal to the value of the failure function f.

Margin of Safety = Reserve Factor – 1.

Activate Failure Theories

Once the First_Ply_Failure method is added to a designpointset, you can edit it from the browser. First, you can select the result level (Element | Layer | Recovery plane), then the type of margin to evaluate.

The failure theories that are available are grouped in categories in the Entity Editor, as per the description in Figure 3. You will activate methods of interest by providing materials to use for failure evaluation (Figure 4). As listed in Figure 3, all failure theories require allowable to be set directly in the referred material entities. Whenever these allowables are meant to be available directly as a solver card (MAT1/MAT8 attributes), they will be queried from the material card. Extra allowables, not available from the solver deck, are automatically created as metadata attached to referenced material entity in HyperMesh. Metadata can be edited in each material Entity Editor. If a metadata already exists, it will not be overridden. Metadata is stored in the HyperMesh binary file along with the model.


Figure 4. First ply failure selection & allowable as metadata

Example 1: Local Post-Processing

A corner supported uniformly pressure-loaded thick cross-ply laminated plate [13]. This tutorial highlights post-processing for four specific elements using two design criteria, namely Max strain and Out-of-plane shear. The latter requires additional strength allowable in the out-of-plane shear direction, which are introduced as HyperMesh metadata.


Figure 5.

Example 2: Global Post-Processing

Filament wound Composite Pressure Vessel (CPV) loaded with internal pressure. The CPV is wound from seven helical GFRP layer pairs and one circumferential CFRP layer pair. FPF results for the CPV are presented in the element level and layer level using Max strain criterion. For comparison, Yamada-Sun criterion-based results are presented in the element level. Finally, post-processing is performed only for the CFRP material using Max fiber stress criterion.


Figure 6.

First Ply Method References

  1. Mechanics of Composite Materials, Jones, R.M., Hemisphere, New York, 1975.
  2. Improved transverse shear stresses in composite finite elements based on first order shear deformation theory, R. Rolfes, K. Rohwer, International Journal for Numerical Methods in Engineering, 40:51–60, 1997.
  3. Failure criteria for an individual layer of a fiber reinforced composite laminate under in-plane loading. ESDU 83014, Amendment A. Engineering Sciences Data Unit, London, 1983/1986.
  4. Structural Materials Handbook, Volume 1 - Polymer Composites. ESA PSS-03-203, Issue 1. ESA Publications Division, ESTEC, Noordwijk, 1994.
  5. Introduction to Composite Materials. Technomic, Tsai, S.W. and Hahn, H.T., Westport, CT, 1980.
  6. Theory of Composite Design, Think Composites, Tsai, S.W., Dayton, OH, 1992.
  7. A Study of Failure Criteria of Fibrous Composite Materials, Paris F., George Washington University, Langley Research Center, Hampton, Virginia, NASA/CR-2001-210661.
  8. Failure Criteria for Unidirectional Fiber Composites, Hashin, Z., Journal of Applied Mechanics, 47 (1980), pp. 329-334.
  9. Failure criteria for non-metallic materials, Implementation of Puck´s failure criterion in ESAComp, FAIL-HPS-TN-003, European Agency Contract Report No. 16162/02/NL/CP, Braunschweig, 2004.
  10. Progressive failure analysis of advanced composites, Camanho P., NASA FA8655-06-1-3072, June 2009.
  11. Advanced Material Models for the Creep Behaviour of Polymer Hard Foams; Latest Advancements of Applied Composite Technology, Roth, M. A., Kraatz, A., Moneke, M., Kolupaev, V., Proceedings 2006 of the SAMPE Europe, 27th International Conference, Paris EXPO, Porte de Versailles, Paris, France, 27th - 29th March 2006. ISBN 3-99522677-2-4. pp. 253 - 2258.
  12. Manual for Structural Stability Analysis of Sandwich Plates and Shells, Sullins, R.T. et al, NASA CR-1457. 1969.
  13. A higher-order plate element for accurate prediction of interlaminar stresses in laminated composite plates, Ramesh S.S., Wang C.M., Reddy J.N. and Ang K.K., Composite Structures 91 (2009) 337–357.

Panel Metallic Failure

The Panel_metallic configuration is shipped with a DLL method called Panel_FailureMode. It computes four possible failure modes for a metallic panel. The method requires shell element forces to be available in the result file. It assumes a valid panel with constant thickness and retrieves thickness information from its structural property. Panel thickness is used to recompute element stress XX, YY, XY. Similarly, the structural property’s material is used to extract tensile/compressive and shear allowable. The method evaluates Margin of Safety as MS= Allowable/Stress -1 for the three directions. For directions one and two (XX and YY), depending on the stress state, either tensile or compressive allowable is used. For shear (XY) absolute stress value is considered in the margin of safety formula.

A fourth failure mode is computed as shear buckling failure of curved panel. In the latter, the highest shear force seen by all elements in the design point is considered. Shear buckling is a ratio of stress with Fscrit = π MathType@MTEF@5@5@+= feaagKart1ev2aaatCvAUfeBSjuyZL2yd9gzLbvyNv2CaerbuLwBLn hiov2DGi1BTfMBaeXatLxBI9gBaerbd9wDYLwzYbItLDharqqtubsr 4rNCHbGeaGqiVu0Je9sqqrpepC0xbbL8F4rqqrFfpeea0xe9Lq=Jc9 vqaqpepm0xbba9pwe9Q8fs0=yqaqpepae9pg0FirpepeKkFr0xfr=x fr=xb9adbaqaaeGaciGaaiaabeqaamaabaabaaGcbaGaeqiWdahaaa@37B3@ 2KcE/(12*(1- v MathType@MTEF@5@5@+= feaagKart1ev2aaatCvAUfeBSjuyZL2yd9gzLbvyNv2CaerbuLwBLn hiov2DGi1BTfMBaeXatLxBI9gBaerbd9wDYLwzYbItLDharqqtubsr 4rNCHbGeaGqiVu0Je9sqqrpepC0xbbL8F4rqqrFfpeea0xe9Lq=Jc9 vqaqpepm0xbba9pwe9Q8fs0=yqaqpepae9pg0FirpepeKkFr0xfr=x fr=xb9adbaqaaeGaciGaaiaabeqaamaabaabaaGcbaGaamODaaaa@36F1@ 2)*(t/b)2 where Kc=Rs+0.2*W2/(R*T).

Rs is available as structural property metadata Radius_shear_constant and the default is 5.35.



Figure 7. Panel Metallic Failure method

Beam Failures

The Beam config has 2 subtypes: Beam_member and Beam_shell. The first is made of 1D elements while the second points to freebody sections. Both configs come with their flavor of the same actual methods:
  1. Stringer Axial Stress
  2. Stringer compressive buckling

The Stinger Axial Stress is a simple method which calculates the Compressive/Tensile margin of safety as:

MS= [(Compressive Stress limit)*(section Area)/(Axial Force)] -1; (resp. Tensile Stress limit)

In the case of freebody sections, Axial Force is mapped to the freebody resultant Fx.

The compressive buckling method evaluates M S = F c c / σ x 1 MathType@MTEF@5@5@+= feaagKart1ev2aaatCvAUfeBSjuyZL2yd9gzLbvyNv2CaerbuLwBLn hiov2DGi1BTfMBaeXatLxBI9gBaerbd9wDYLwzYbItLDharqqtubsr 4rNCHbGeaGqiVu0Je9sqqrpepC0xbbL8F4rqqrFfpeea0xe9Lq=Jc9 vqaqpepm0xbba9pwe9Q8fs0=yqaqpepae9pg0FirpepeKkFr0xfr=x fr=xb9adbaqaaeGaciGaaiaabeqaamaabaabaaGcbaGaamytaiaado facqGH9aqpcaWGgbWaaSbaaSqaaiaadogacaWGJbaabeaakiaac+ca cqaHdpWCdaWgaaWcbaGaamiEaaqabaGccqGHsislcaaIXaaaaa@40C8@ with:
  • σ x MathType@MTEF@5@5@+= feaagKart1ev2aaatCvAUfeBSjuyZL2yd9gzLbvyNv2CaerbuLwBLn hiov2DGi1BTfMBaeXatLxBI9gBaerbd9wDYLwzYbItLDharqqtubsr 4rNCHbGeaGqiVu0Je9sqqrpepC0xbbL8F4rqqrFfpeea0xe9Lq=Jc9 vqaqpepm0xbba9pwe9Q8fs0=yqaqpepae9pg0FirpepeKkFr0xfr=x fr=xb9adbaqaaeGaciGaaiaabeqaamaabaabaaGcbaGaeq4Wdm3aaS baaSqaaiaadIhaaeqaaaaa@38E2@ : average axial stress as (Axial Force)/(Section’s area)
  • F cc = F cy *(1.272(L'/ρ)/π* E/ F cy ) MathType@MTEF@5@5@+= feaagKart1ev2aaatCvAUfeBSjuyZL2yd9gzLbvyNv2CaerbuLwBLn hiov2DGi1BTfMBaeXatLxBI9gBaerbd9wDYLwzYbItLDharqqtubsr 4rNCHbGeaGqiVu0Je9sqqrpepC0xbbL8F4rqqrFfpeea0xe9Lq=Jc9 vqaqpepm0xbba9pwe9Q8fs0=yqaqpepae9pg0FirpepeKkFr0xfr=x fr=xb9adbaqaaeGaciGaaiaabeqaamaabaabaaGcbaGaamOramaaBa aaleaacaWGJbGaam4yaaqabaGccqGH9aqpcaWGgbWaaSbaaSqaaiaa dogacaWG5baabeaakiaacQcacaGGOaGaaGymaiabgkHiTiaac6caca aIYaGaaG4naiaaikdacaGGOaGaamitaiaacEcacaGGVaGaeqyWdiNa aiykaiaac+cacqaHapaCcaGGQaWaaOaaaeaacaWGfbGaai4laiaadA eadaWgaaWcbaGaam4yaiaadMhaaeqaaaqabaGccaGGPaaaaa@5028@
  • F c y MathType@MTEF@5@5@+= feaagKart1ev2aaatCvAUfeBSjuyZL2yd9gzLbvyNv2CaerbuLwBLn hiov2DGi1BTfMBaeXatLxBI9gBaerbd9wDYLwzYbItLDharqqtubsr 4rNCHbGeaGqiVu0Je9sqqrpepC0xbbL8F4rqqrFfpeea0xe9Lq=Jc9 vqaqpepm0xbba9pwe9Q8fs0=yqaqpepae9pg0FirpepeKkFr0xfr=x fr=xb9adbaqaaeGaciGaaiaabeqaamaabaabaaGcbaGaamOramaaBa aaleaacaWGJbGaamyEaaqabaaaaa@38D3@ : material compressive stress limit
  • L ' = ( structural property L e n g t h ) / K_constraint MathType@MTEF@5@5@+= feaagKart1ev2aaatCvAUfeBSjuyZL2yd9gzLbvyNv2CaerbuLwBLn hiov2DGi1BTfMBaeXatLxBI9gBaerbd9wDYLwzYbItLDharqqtubsr 4rNCHbGeaGqiVu0Je9sqqrpepC0xbbL8F4rqqrFfpeea0xe9Lq=Jc9 vqaqpepm0xbba9pwe9Q8fs0=yqaqpepae9pg0FirpepeKkFr0xfr=x fr=xb9adbaqaaeGaciGaaiaabeqaamaabaabaaGcbaGaamitaiaacE cacqGH9aqpcaGGOaGaae4CaiaabshacaqGYbGaaeyDaiaabogacaqG 0bGaaeyDaiaabkhacaqGHbGaaeiBaiaaysW7caqGWbGaaeOCaiaab+ gacaqGWbGaaeyzaiaabkhacaqG0bGaaeyEaiaaygW7caaMb8UaaGjb VlaadYeacaWGLbGaamOBaiaadEgacaWG0bGaamiAaiaacMcacaGGVa WaaOaaaeaacaqGlbGaae4xaiaabogacaqGVbGaaeOBaiaabohacaqG 0bGaaeOCaiaabggacaqGPbGaaeOBaiaabshaaSqabaaaaa@6274@
    • K_constraint = “constraint coefficient” on structural property. Def=0.0699
  • ρ MathType@MTEF@5@5@+= feaagKart1ev2aaatCvAUfeBSjuyZL2yd9gzLbvyNv2CaerbuLwBLn hiov2DGi1BTfMBaeXatLxBI9gBaerbd9wDYLwzYbItLDharqqtubsr 4rNCHbGeaGqiVu0Je9sqqrpepC0xbbL8F4rqqrFfpeea0xe9Lq=Jc9 vqaqpepm0xbba9pwe9Q8fs0=yqaqpepae9pg0FirpepeKkFr0xfr=x fr=xb9adbaqaaeGaciGaaiaabeqaamaabaabaaGcbaGaeqyWdihaaa@37B6@ : beam section’s radius of gyration
  • E: material young’s modulus