ERRI

Computing Margin of Safety with ERRI B12 RP60.

Margin of Safety (MS) is evaluated using the following equation, derived from the Haigh diagram shown in Figure 1.(1)

M S = (1 - \frac{σ_{a c t u a l}}{σ_{a d m i s s i b l e}}) \times 100

$σ_{a}$ = Stress Amplitude

$σ_{m}$ = Mean Stress

HyperLife calculates Margin of Safety using Haigh Diagram or SN curve assigned to the part.

With single or multiple Haigh Diagrams, mean stress correction should be set to INTERPOLATE. If single SN curve, margin of safety is evaluated based on the mean stress model selected. (Similar to Safety Factor evaluated in Stress Life uniaxial: Uniaxial Fatigue Analysis)

Unwelded evaluation for margin of safety supports identification of worst subcase pair using Range Envelope Configuration. Range Envelope is based on maximum principal range among all the subcases assigned in the fatigue event.

Note: With Event configuration : Range Envelope. Stress range projected in the max principal direction of the worst subcase combination can be used for unwelded evaluation by using the Use projected stress in unwelded evaluation option in preferences.

From the worst subcase tensors projected in the max principal tensor direction can be applied by toggling.

Following are the parameters listed in Assign Material.

Parameter	Description
Material	Material assigned to the Part. Material list for selection is created by adding Materials to Assign Material list from Material Db, My Material or HM Material tabs.
Material Units	Unit of the assigned material.
Plot	Stress Life plot of the assigned material.
FL	Fatigue Limit of the assigned material.
SE	Standard Error of Log(N) of the assigned material. Default = 0.0 (Real ≥ 0.0)
FKMMSS	Mean Stress Sensitivity parameters for mean stress correction based on FKM Guidelines. Default: MSS1 = 0.0 MSS2 = 0.15 MSS3 = 0.0 MSS4 = 0.0
Scale	Scale is used to modify the calculated stress during the stress history generation.
Offset	Offset is used to modify the calculated stress during the stress history generation.
Finish	Material Surface Finish, a result of manufacturing process. NONE (Default), POLISH GROUND MACHINE HOTROLL FORGE Or USER (any float value between 0.0 and 1.0.) When it is a float value, it will be used to modify the fatigue limit by multiplied with the original fatigue limit. Read more: Other Factors Affecting Fatigue
Surf Treatment	Material Surface Treatment for Material S-N Curve, a process used to enhance the fatigue life. NONE (Default) NITRIDED SHOTPEEN COLDROLL Or USER any float value greater than 0.0. When it is a float value, it will be used to modify the fatigue limit by multiplied with the original fatigue limit. Read more: Other Factors Affecting Fatigue
Temperature factor	Temperature influence can be accounted by applying the temperature factor C_temp to modify the fatigue endurance limit FL. Read more: Other Factors Affecting Fatigue
Kf	Fatigue strength reduction factor. Default = 1.0 (Real ≥ 1.0) Read more: Other Factors Affecting Fatigue

Note: Stress life for evaluation domain: unwelded is supported only for shell elements via elemental evaluation.

ERRI evaluation supports Time Series loading and allows creation of Superposition/Sequential/Range Envelope fatigue events. Refer to: Create Events.