Safety Factor Display Manipulation/Controls

Overview of the display options and controls for Safety factor contours.

Safety factor contours are presented in 3 color bands (red, yellow and blue). The threshold between bands are controlled by the Safety Factor LOW and Safety Factor HIGH values. The factors act as multipliers on the criterion value and reflect the degree of uncertainty that the user is looking to tolerate. For example, a LOW safety factor value of 1.25 indicates a 25% safety margin on the failure criterion value.
Figure 1.


  • Update the LOW or HIGH fields to change the threshold values. You can manipulate the threshold values in real time using the slider in the dialog.
  • To change the failure, you must edit the material property definition in the material database. The Standard database is read only and cannot be edited, so you will need to create a new database and copy materials. Learn more about manipulating materials here.
  • Change the default criterion from the Material database.
    Figure 2.


    Safety factors are not plotted for materials with Not Specified failure criterion.
Note: When assigning materials, SimSolid Cloud makes a local copy of each material property in the project file. Changes to material properties in the database are not updated in the model. You must reapply the material and rerun the analysis to see this change.

Potential Material Failure Analysis - Safety Factor

Safety factor plots are used to characterize zones of possible material failure.

Failure Criterion

SimSolid Cloud safety factor plots are used to characterize zones of possible material failure. The are simple three color contours that highlight areas of possible material yielding. In SimSolid Cloud, static structural analysis is linear elastic, so areas where the material yields should be recognized and designed out.
Figure 3.


Different failure criteria can be calculated quickly and the results dynamically updated. The material failure condition is expressed by the following inequality:

Criterion Value < 1

If the inequality is met, the material is considered safe. Criterion Value depends on the stress state of the material at a given location. Safety Factor is the inverse to the Criterion Value. Dividing both sides of the inequality by the Criterion Value, one obtains the failure condition expressed through the Safety Factor:

Safety Factor = 1/Criterion Value

Note: Proper failure criterion is material and application specific. It also reflects the degree of conservatism considered appropriate for the particular design. While default criterion are provided for each SimSolid material, they should be considered as examples only. The ultimate decision of which criterion to use is the responsibility of the design engineer.

Safety Zone Contours in SimSolid

Safety zone contours are presented in 3 color bands (red, yellow and green). The threshold between bands are controlled by the Safety Factor Low and Safety Factor High values. The factors act as multipliers on the criterion value and reflect the degree of uncertainty that you are looking to tolerate. For example, a safety factor value of 1.25 indicates a 25% safety margin on the failure criterion value.

Failure Theories

Failure theories are material specific and their formulation is dependent on the type of material being considered.
Ductile Materials
In ductile materials, failure takes place by yielding. Ductile materials includes most metals and some plastics. The material tensile yield strength (TYS) is used to determine the working stress. Prior to yield, material response is assumed to be elastic.
Figure 4.


Many steels, especially heat-treated materials, do not have a well-defined elastic limit. In this case, the yield strength is usually defined at the point where the plastic strain is about 0.1% to 0.2%

CAUTION:

Steel is often thought of as a ductile material. However this is not always the case. At low temperatures on the order of 20°to 40° F (-7° to 5° C) many steels begin to lose their ductile properties. Below some transition temperature, you can no longer treat steel like a ductile material.

It is recommended that you contact the material supplier for best practices on how to determine material failure.

Brittle Materials
In brittle materials, failure takes place by fracture, therefore the criteria of failure is different from that for ductile materials. The fracture stress in compression is much larger than that in tension.
Figure 5.


The failure theories available in SimSolid are as follows:
Max von Mises Stress

Most appropriate for ductile materials, this theory is also known as the maximum distortion energy criterion, octahedral shear stress theory or Maxwell-Huber-Hencky-von Mises theory. It is computed as the ratio of the material’s tensile yield strength to the von Mises stress and is usually considered to be the best fit with experiment results.

Max Shear Stress
Most appropriate for ductile materials, this theory is also known as Tresca's or Guest's criterion. It states that yielding begins whenever the maximum shear stress in the model becomes equal to the maximum shear stress in a tension test specimen that has begun to yield. As compared to the Max von Mises Stress theory, Max Shear Stress is a more conservative approach. In some cases, it can over-estimate stress by 15%.
Max Normal Stress
Most appropriate for brittle materials, this theory is also known as Coulomb’s criterion. It is computed by examining the ratio of the material’s tensile and compressive strength to the max principal stresses.
Christensen
This is a more recent theory that tries to bridge the gap between failure criteria for ductile and brittle materials. The Christensen failure criterion is composed of two separate subcriteria representing competitive failure mechanisms. One has a quadratic form similar to the von Mises criterion and the other is a Coordinated Fracture criterion similar to the Coulomb-Mohr criterion.

Failure Criterion Formulas

Table 1.
Criterion Formula
Max von Mises Stress SF   =   σ tensile   yield σ von   Mises MathType@MTEF@5@5@+= feaahqart1ev3aaatCvAUfeBSjuyZL2yd9gzLbvyNv2CaerbuLwBLn hiov2DGi1BTfMBaeXatLxBI9gBaerbd9wDYLwzYbItLDharqqtubsr 4rNCHbGeaGqiVu0Je9sqqrpepC0xbbL8F4rqqrFfpeea0xe9Lq=Jc9 vqaqpepm0xbba9pwe9Q8fs0=yqaqpepae9pg0FirpepeKkFr0xfr=x fr=xb9adbaqaaeGaciGaaiaabeqaamaabaabaaGcbaGaae4uaiaabA eacaaMc8UaaeypaiaaykW7daWcaaqaaiaabo8adaWgaaWcbaGaaeiD aiaabwgacaqGUbGaae4CaiaabMgacaqGSbGaaeyzaiaaysW7caqG5b GaaeyAaiaabwgacaqGSbGaaeizaaqabaaakeaacaqGdpWaaSbaaSqa aiaabAhacaqGVbGaaeOBaiaaysW7caqGnbGaaeyAaiaabohacaqGLb Gaae4Caaqabaaaaaaa@5421@
Max Shear Stress SF   =   σ tensile   yield 2   τ max MathType@MTEF@5@5@+= feaahqart1ev3aaatCvAUfeBSjuyZL2yd9gzLbvyNv2CaerbuLwBLn hiov2DGi1BTfMBaeXatLxBI9gBaerbd9wDYLwzYbItLDharqqtubsr 4rNCHbGeaGqiVu0Je9sqqrpepC0xbbL8F4rqqrFfpeea0xe9Lq=Jc9 vqaqpepm0xbba9pwe9Q8fs0=yqaqpepae9pg0FirpepeKkFr0xfr=x fr=xb9adbaqaaeGaciGaaiaabeqaamaabaabaaGcbaGaae4uaiaabA eacaaMc8UaaeypaiaaykW7daWcaaqaaiaabo8adaWgaaWcbaGaaeiD aiaabwgacaqGUbGaae4CaiaabMgacaqGSbGaaeyzaiaaysW7caqG5b GaaeyAaiaabwgacaqGSbGaaeizaaqabaaakeaacaaIYaGaaGPaVlab es8a0naaBaaaleaaciGGTbGaaiyyaiaacIhaaeqaaaaaaaa@50BF@

where:

τ max =   maximum     σ 1 − σ 2 2 , σ 2 − σ 3 2 , σ 3 − σ 1 2 MathType@MTEF@5@5@+= feaahqart1ev3aaatCvAUfeBSjuyZL2yd9gzLbvyNv2CaerbuLwBLn hiov2DGi1BTfMBaeXatLxBI9gBaerbd9wDYLwzYbItLDharqqtubsr 4rNCHbGeaGqiVu0Je9sqqrpepC0xbbL8F4rqqrFfpeea0xe9Lq=Jc9 vqaqpepm0xbba9pwe9Q8fs0=yqaqpepae9pg0FirpepeKkFr0xfr=x fr=xb9adbaqaaeGaciGaaiaabeqaamaabaabaaGcbaGaaeiXdmaaBa aaleaacaqGTbGaaeyyaiaabIhaaeqaaOGaaeypaiaaykW7caqGTbGa aeyyaiaabIhacaqGPbGaaeyBaiaabwhacaqGTbGaaGjcVlaaykW7da qadaqaamaaemaabaWaaSaaaeaacqaHdpWCdaWgaaWcbaGaaGymaaqa baGccqGHsislcqaHdpWCdaWgaaWcbaGaaGOmaaqabaaakeaacaaIYa aaaaGaay5bSlaawIa7aiaacYcadaabdaqaamaalaaabaGaeq4Wdm3a aSbaaSqaaiaaikdaaeqaaOGaeyOeI0Iaeq4Wdm3aaSbaaSqaaiaaio daaeqaaaGcbaGaaGOmaaaaaiaawEa7caGLiWoacaGGSaWaaqWaaeaa daWcaaqaaiabeo8aZnaaBaaaleaacaaIZaaabeaakiabgkHiTiabeo 8aZnaaBaaaleaacaaIXaaabeaaaOqaaiaaikdaaaaacaGLhWUaayjc SdaacaGLOaGaayzkaaaaaa@67F4@

Max Normal Stress SF i   =   σ tensile   yield σ i MathType@MTEF@5@5@+= feaahqart1ev3aaatCvAUfeBSjuyZL2yd9gzLbvyNv2CaerbuLwBLn hiov2DGi1BTfMBaeXatLxBI9gBaerbd9wDYLwzYbItLDharqqtubsr 4rNCHbGeaGqiVu0Je9sqqrpepC0xbbL8F4rqqrFfpeea0xe9Lq=Jc9 vqaqpepm0xbba9pwe9Q8fs0=yqaqpepae9pg0FirpepeKkFr0xfr=x fr=xb9adbaqaaeGaciGaaiaabeqaamaabaabaaGcbaGaae4uaiaabA eadaWgaaWcbaGaaeyAaaqabaGccaaMc8UaaeypaiaaykW7daWcaaqa aiaabo8adaWgaaWcbaGaaeiDaiaabwgacaqGUbGaae4CaiaabMgaca qGSbGaaeyzaiaaysW7caqG5bGaaeyAaiaabwgacaqGSbGaaeizaaqa baaakeaacaqGdpWaaSbaaSqaaiaabMgaaeqaaaaaaaa@4D36@ if σ i MathType@MTEF@5@5@+= feaahqart1ev3aaatCvAUfeBSjuyZL2yd9gzLbvyNv2CaerbuLwBLn hiov2DGi1BTfMBaeXatLxBI9gBaerbd9wDYLwzYbItLDharqqtubsr 4rNCHbGeaGqiVu0Je9sqqrpepC0xbbL8F4rqqrFfpeea0xe9Lq=Jc9 vqaqpepm0xbba9pwe9Q8fs0=yqaqpepae9pg0FirpepeKkFr0xfr=x fr=xb9adbaqaaeGaciGaaiaabeqaamaabaabaaGcbaGaae4WdmaaBa aaleaacaqGPbaabeaaaaa@3854@ > 0 and

SF i   =   σ compressive   yield σ i MathType@MTEF@5@5@+= feaahqart1ev3aaatCvAUfeBSjuyZL2yd9gzLbvyNv2CaerbuLwBLn hiov2DGi1BTfMBaeXatLxBI9gBaerbd9wDYLwzYbItLDharqqtubsr 4rNCHbGeaGqiVu0Je9sqqrpepC0xbbL8F4rqqrFfpeea0xe9Lq=Jc9 vqaqpepm0xbba9pwe9Q8fs0=yqaqpepae9pg0FirpepeKkFr0xfr=x fr=xb9adbaqaaeGaciGaaiaabeqaamaabaabaaGcbaGaae4uaiaabA eadaWgaaWcbaGaaeyAaaqabaGccaaMc8UaaeypaiaaykW7daWcaaqa aiaabo8adaWgaaWcbaGaae4yaiaab+gacaqGTbGaaeiCaiaabkhaca qGLbGaae4CaiaabohacaqGPbGaaeODaiaabwgacaaMe8UaaeyEaiaa bMgacaqGLbGaaeiBaiaabsgaaeqaaaGcbaGaae4WdmaaBaaaleaaca qGPbaabeaaaaaaaa@50FE@ if σ i MathType@MTEF@5@5@+= feaahqart1ev3aaatCvAUfeBSjuyZL2yd9gzLbvyNv2CaerbuLwBLn hiov2DGi1BTfMBaeXatLxBI9gBaerbd9wDYLwzYbItLDharqqtubsr 4rNCHbGeaGqiVu0Je9sqqrpepC0xbbL8F4rqqrFfpeea0xe9Lq=Jc9 vqaqpepm0xbba9pwe9Q8fs0=yqaqpepae9pg0FirpepeKkFr0xfr=x fr=xb9adbaqaaeGaciGaaiaabeqaamaabaabaaGcbaGaae4WdmaaBa aaleaacaqGPbaabeaaaaa@3854@ < 0 for i = 1, 2, 3

SF   =   minimum   SF 1 ,   SF 2 ,   SF 3 MathType@MTEF@5@5@+= feaahqart1ev3aaatCvAUfeBSjuyZL2yd9gzLbvyNv2CaerbuLwBLn hiov2DGi1BTfMBaeXatLxBI9gBaerbd9wDYLwzYbItLDharqqtubsr 4rNCHbGeaGqiVu0Je9sqqrpepC0xbbL8F4rqqrFfpeea0xe9Lq=Jc9 vqaqpepm0xbba9pwe9Q8fs0=yqaqpepae9pg0FirpepeKkFr0xfr=x fr=xb9adbaqaaeGaciGaaiaabeqaamaabaabaaGcbaGaae4uaiaabA eacaaMc8UaaeypaiaaykW7caqGTbGaaeyAaiaab6gacaqGPbGaaeyB aiaabwhacaqGTbGaaGPaVpaabmaabaGaae4uaiaabAeadaWgaaWcba GaaeymaaqabaGccaqGSaGaaGPaVlaabofacaqGgbWaaSbaaSqaaiaa bkdaaeqaaOGaaeilaiaaykW7caqGtbGaaeOramaaBaaaleaacaqGZa aabeaaaOGaayjkaiaawMcaaaaa@511F@

Christensen if σ tensile σ compressive   ≤ 1 2 MathType@MTEF@5@5@+= feaahqart1ev3aaatCvAUfeBSjuyZL2yd9gzLbvyNv2CaerbuLwBLn hiov2DGi1BTfMBaeXatLxBI9gBaerbd9wDYLwzYbItLDharqqtubsr 4rNCHbGeaGqiVu0Je9sqqrpepC0xbbL8F4rqqrFfpeea0xe9Lq=Jc9 vqaqpepm0xbba9pwe9Q8fs0=yqaqpepae9pg0FirpepeKkFr0xfr=x fr=xb9adbaqaaeGaciGaaiaabeqaamaabaabaaGcbaWaaeWaaeaada Wcaaqaaiaabo8adaWgaaWcbaGaaeiDaiaabwgacaqGUbGaae4Caiaa bMgacaqGSbGaaeyzaaqabaaakeaacaqGdpWaaSbaaSqaaiaabogaca qGVbGaaeyBaiaabchacaqGYbGaaeyzaiaabohacaqGZbGaaeyAaiaa bAhacaqGLbaabeaaaaGccaaMc8UaeyizIm6aaSaaaeaacaqGXaaaba GaaeOmaaaaaiaawIcacaGLPaaaaaa@501D@ then SF 1   =   σ tensile σ 1 ,   SF 2   =   σ tensile σ 2 ,   SF 3   =   σ tensile σ 3 MathType@MTEF@5@5@+= feaahqart1ev3aaatCvAUfeBSjuyZL2yd9gzLbvyNv2CaerbuLwBLn hiov2DGi1BTfMBaeXatLxBI9gBaerbd9wDYLwzYbItLDharqqtubsr 4rNCHbGeaGqiVu0Je9sqqrpepC0xbbL8F4rqqrFfpeea0xe9Lq=Jc9 vqaqpepm0xbba9pwe9Q8fs0=yqaqpepae9pg0FirpepeKkFr0xfr=x fr=xb9adbaqaaeGaciGaaiaabeqaamaabaabaaGcbaGaae4uaiaabA eadaWgaaWcbaGaaeymaaqabaGccaaMc8UaaeypaiaaykW7daWcaaqa aiaabo8adaWgaaWcbaGaaeiDaiaabwgacaqGUbGaae4CaiaabMgaca qGSbGaaeyzaaqabaaakeaacaqGdpWaaSbaaSqaaiaabgdaaeqaaaaa kiaabYcacaaMe8Uaae4uaiaabAeadaWgaaWcbaGaaeOmaaqabaGcca aMc8UaaeypaiaaykW7daWcaaqaaiaabo8adaWgaaWcbaGaaeiDaiaa bwgacaqGUbGaae4CaiaabMgacaqGSbGaaeyzaaqabaaakeaacaqGdp WaaSbaaSqaaiaabkdaaeqaaaaakiaabYcacaaMe8Uaae4uaiaabAea daWgaaWcbaGaae4maaqabaGccaaMc8UaaeypaiaaykW7daWcaaqaai aabo8adaWgaaWcbaGaaeiDaiaabwgacaqGUbGaae4CaiaabMgacaqG SbGaaeyzaaqabaaakeaacaqGdpWaaSbaaSqaaiaabodaaeqaaaaaaa a@6C65@

SF 4   =   1 E Q MathType@MTEF@5@5@+= feaahqart1ev3aaatCvAUfeBSjuyZL2yd9gzLbvyNv2CaerbuLwBLn hiov2DGi1BTfMBaeXatLxBI9gBaerbd9wDYLwzYbItLDharqqtubsr 4rNCHbGeaGqiVu0Je9sqqrpepC0xbbL8F4rqqrFfpeea0xe9Lq=Jc9 vqaqpepm0xbba9pwe9Q8fs0=yqaqpepae9pg0FirpepeKkFr0xfr=x fr=xb9adbaqaaeGaciGaaiaabeqaamaabaabaaGcbaGaae4uaiaabA eadaWgaaWcbaGaaGinaaqabaGccaaMc8UaaeypaiaaykW7daWcaaqa aiaaigdaaeaadaGcaaqaaiaadweacaWGrbaaleqaaaaaaaa@3EE2@

SF   =   minimum   SF 1 ,   SF 2 ,   SF 3 ,   SF 4 MathType@MTEF@5@5@+= feaahqart1ev3aaatCvAUfeBSjuyZL2yd9gzLbvyNv2CaerbuLwBLn hiov2DGi1BTfMBaeXatLxBI9gBaerbd9wDYLwzYbItLDharqqtubsr 4rNCHbGeaGqiVu0Je9sqqrpepC0xbbL8F4rqqrFfpeea0xe9Lq=Jc9 vqaqpepm0xbba9pwe9Q8fs0=yqaqpepae9pg0FirpepeKkFr0xfr=x fr=xb9adbaqaaeGaciGaaiaabeqaamaabaabaaGcbaGaae4uaiaabA eacaaMc8UaaeypaiaaykW7caqGTbGaaeyAaiaab6gacaqGPbGaaeyB aiaabwhacaqGTbGaaGPaVpaabmaabaGaae4uaiaabAeadaWgaaWcba GaaeymaaqabaGccaqGSaGaaGjbVlaabofacaqGgbWaaSbaaSqaaiaa bkdaaeqaaOGaaeilaiaaysW7caqGtbGaaeOramaaBaaaleaacaqGZa aabeaakiaabYcacaaMe8Uaae4uaiaabAeadaWgaaWcbaGaaeinaaqa baaakiaawIcacaGLPaaaaaa@55EB@

where:

EQ   =   1 σ tensile   -   1 σ compressive   σ 1 +σ 2 +σ 3   +   1 σ yield σ compressive   σ von   Mises 2 MathType@MTEF@5@5@+= feaahqart1ev3aaatCvAUfeBSjuyZL2yd9gzLbvyNv2CaerbuLwBLn hiov2DGi1BTfMBaeXatLxBI9gBaerbd9wDYLwzYbItLDharqqtubsr 4rNCHbGeaGqiVu0Je9sqqrpepC0xbbL8F4rqqrFfpeea0xe9Lq=Jc9 vqaqpepm0xbba9pwe9Q8fs0=yqaqpepae9pg0FirpepeKkFr0xfr=x fr=xb9adbaqaaeGaciGaaiaabeqaamaabaabaaGcbaGaaeyraiaabg facaaMc8UaaeypaiaaykW7daqadaqaamaalaaabaGaaeymaaqaaiaa bo8adaWgaaWcbaGaaeiDaiaabwgacaqGUbGaae4CaiaabMgacaqGSb GaaeyzaaqabaaaaOGaaGjbVlaab2cacaaMe8+aaSaaaeaacaqGXaaa baGaae4WdmaaBaaaleaacaqGJbGaae4Baiaab2gacaqGWbGaaeOCai aabwgacaqGZbGaae4CaiaabMgacaqG2bGaaeyzaaqabaaaaaGccaGL OaGaayzkaaGaaGPaVpaabmaabaGaae4WdmaaBaaaleaacaqGXaaabe aakiaabUcacaqGdpWaaSbaaSqaaiaabkdaaeqaaOGaae4kaiaabo8a daWgaaWcbaGaae4maaqabaaakiaawIcacaGLPaaacaaMc8Uaae4kai aaykW7daqadaqaamaalaaabaGaaeymaaqaaiaabo8adaWgaaWcbaGa aeyEaiaabMgacaqGLbGaaeiBaiaabsgaaeqaaOGaae4WdmaaBaaale aacaqGJbGaae4Baiaab2gacaqGWbGaaeOCaiaabwgacaqGZbGaae4C aiaabMgacaqG2bGaaeyzaaqabaaaaaGccaGLOaGaayzkaaGaaGPaVp aabmaabaGaae4WdmaaBaaaleaacaqG2bGaae4Baiaab6gacaaMe8Ua aeytaiaabMgacaqGZbGaaeyzaiaabohaaeqaaOWaaWbaaSqabeaaca qGYaaaaaGccaGLOaGaayzkaaaaaa@87A2@