automated calculation of stress concentrations around holes using the com interface of stresscheck

Automated calculation of Stress Concentrations

around Holes using the COM Interface of

StressCheck

Luzian Michel, RUAG Aviation

EATC 2014, Munich

25.06.2014

Motivation

Up to now stress concentrations of loaded fastener holes are

being calculated using the methodology of known literature such

as Peterson.

The whole process takes a considerable amount of time

loads have to be extracted from the FEM

divided in the unit conditions according to Peterson (manually!)

a clocking analysis has to be performed.

Process is error prone and time consuming as it has to be done

by hand

GOAL: Develop a tool which performs automatically a full 3D FE

analysis based on a 2D FE model

02.07.2014 │RUAG Aviation│ 2

Why StressCheck?

StressCheck is a p-type FEA software

High accuracy through use of higher order polynoms instead of high

element count

Low computational time!

Most of StressChecks functions can be used through a COM API

Prerequisite for automated analysis

StressCheck includes

Pre processor

Solver

Post processor

StressCheck is available through the Altair Partner Alliance Program


Working principle


HyperMesh

• Load model

• Extract freebody (geometry, materials, loads, fastener info)

Excel

• Store freebody information

• Run StressCheck macro

StressCheck

• Build geometry & assign properties

• Apply loads & boundary conditions

• Perform analysis & extract results

Excel

• Write Results Sheet

Example


Step 1: GUI


HyperMesh

Step 2: Extract Data from FEM

Read geometry

Node locations

Elements (CQUAD /CTRIA)

Properties

Material

Read fastener information (CBUSH-Elements)

Diameter

Material

Fit

Countersink


HyperMesh

Step 3: Build up Excel database

Write all data to a spreadsheet

Transform the forces to a text file for the import to StressCheck


HyperMesh

Excel

Step 4: StressCheck Model

Create 2D geometry in StressCheck

based on Elements from DFEM

Extrude 2D geometry to the required thickness

Subtract fastener holes

Countersink is not being modeled

Automesh

Pentamesh for flat geometries

Tetramesh for anything else


HyperMesh

Excel

StressCheck

Step 4: StressCheck Model


HyperMesh

Excel

StressCheck

Step 5: Loads

Import nodal forces and moments

Apply forces and moments to the borders of the plate


Source: StressCheck 9.2 Master Guide

HyperMesh

Excel

StressCheck

Step 5: Loads

Import fastener loads

Apply the loads on holes in structure


Source: StressCheck 9.2 Master Guide

Forces Moments

HyperMesh

Excel

StressCheck

Step 6: Solve & Evaluate Stresses

Solve StressCheck model.

Read tangential stress around

hole

Top and Bottom Surface

Midthickness

Determine StressCheck solver

error

Create report sheet for each

analysis


HyperMesh

Excel

StressCheck

Step 7: Report

Create report sheet for each

analysis


HyperMesh

Excel

StressCheck

Excel

Evaluation


Open-Hole Cases

Test Scenario: Open Hole with thru stress

2 different thicknesses tested

d/H = 0.25

d/l = 0.25

From literature:


Source: Peterson 2nd Ed., Chart 4.33

𝜎𝑚𝑎𝑥

𝜎= 3.13

Open-Hole Cases

Impact study performed to assess:

Edge effect

Shadowing factors

Thickness effects

Example model:


Open-Hole Cases


B1

B2

B3

B4

B5

Open-Hole Case - Results

Results:

Conclusions

Mean-values a bit below, peak values a bit too high

The larger the area the better is the result

Thickness effect is considered in the analysis


B1 B2 B3 B4 B5 Ref. value

Mean ktσ

t=0.2 in. 3.37 3.29 3.19 3.19 3.19 3.25

t=0.0625 in. 3.53 3.33 3.16 3.16 3.17 3.16

Peak ktσ

t=0.2 in. 3.45 3.38 3.29 3.29 3.30 3.25

t=0.0625 in. 3.58 3.38 3.20 3.19 3.20 3.16

Thickness factors incl.

Off-Axis loading

Lug is modelled in StressCheck

Analysis performed for

2D

3D

As reference a second model was created in Hypermesh

2D

Sin distributed loads

Variation of the load angle θ


Off-Axis loading

Comparison StressCheck 2D ↔ 3D

Very good comparison for small load angles. Variations exist for other

load angles.


-2,00E+00

-1,00E+00

0,00E+00

1,00E+00

2,00E+00

3,00E+00

4,00E+00

5,00E+00

0 20 40 60 80 100 120 140 160 180

kt(

ph

i)

theta [°]

phi=0°

phi=10°

phi=20°

phi=30°

phi=40°

phi=50°

phi=60°

phi=70°-2,00E+00

-1,00E+00

0,00E+00

1,00E+00

2,00E+00

3,00E+00

4,00E+00

5,00E+00

0 20 40 60 80 100 120 140 160 180

kt(

ph

i)

theta [°]

phi=0°

phi=10°

phi=20°

phi=30°

phi=40°

phi=50°

phi=60°

phi=70°

2D 3D

Off-Axis loading

Comparison StressCheck ↔ Hypermesh (2D, sinusoidal load)

Good match between StressCheck und HyperMesh. Some variation

exists for higher load angles.


-2,00E+00

-1,00E+00

0,00E+00

1,00E+00

2,00E+00

3,00E+00

4,00E+00

5,00E+00

0 20 40 60 80 100 120 140 160 180

kt(

ph

i)

theta [°]

phi=0°

phi=10°

phi=20°

phi=30°

phi=40°

phi=50°

phi=60°

phi=70° -2,00E+00

-1,00E+00

0,00E+00

1,00E+00

2,00E+00

3,00E+00

4,00E+00

5,00E+00

0 20 40 60 80 100 120 140 160 180kt(

ph

i)

theta [°]

phi=0°

phi=10°

phi=20°

phi=30°

phi=40°

phi=50°

phi=60°

phi=70°

StressCheck HyperMesh

Off-Axis loading

Conclusions:

2D models show higher Kt values than 3D models

Good match between the FE programs StressCheck and Hypermesh

Overall good match to literature data


Outlook

Include pin-bending effect

Countersink modeling


Thank you!

Any Questions?


automated calculation of stress concentrations around holes using the com interface of stresscheck

Engineering