US 11,958,137 B2Granted

Unified fatigue life evaluation method for welded structures

AssigneeThe Regents of the University of Michigan

InventorsPingsha Dong, Xianjun Pei, Jifa Mei

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Abstract

Due to geometric discontinuities introduced by welding and joining processes, stresses or strain cannot be calculated reliably calculated using modern analytical and computer methods as result of stress or strain singularity at joint locations, which leads to severe mesh sensitivity. Design and fatigue evaluation of these structures remain empirical. This disclosure addresses mesh insensitivity of stress/strain calculations for welded structures through a cut-plane traction stress method through a novel post processing of conventional finite element computation results, as well as provides a unified fatigue evaluation procedure for fatigue design and structural life evaluation for both low-cycle and high cycle fatigue regime subjected to either proportional or non-proportional multiaxial fatigue loading, as well as a simple and reliable method for treating spot welds.

Claims10

Dependent claims

A unified method for estimating fatigue for a welded structure under load, comprising:

generating a finite element model for a given structure;
calculating a distribution of structural stress within the given structure using the finite element model and while the given structure is under a given load, where the distribution of stress is determined in relation to a plane intersecting the given structure;
determining whether stress exceeds yield strength of material comprising the given structure;
calculating a distribution of structural strain experienced within the given structure using Hooks law in response to a determination that the stress is less than yield strength of material;
calculating a distribution of structural strain experienced within the given structure using an analytic method in response to a determination that the stress exceeds yield strength of material, where the distribution of structural strain is calculated in part from the calculated distribution of structural stress and the distribution of structural strain is defined in relation to the plane by at least two closed-form expressions which account for stress that exceeds yield strength of material;
and
calculating a fatigue life for the given structure when placed under the given load using the calculated distribution of structural strain using a master E-N curve, wherein, for a spot weld, the distribution of structural stress within the given structure is calculated by
modeling a spot weld as a beam coupled between two or more plates;
defining a square area that encapsulates the spot weld;
extracting nodal forces and moments along the edges of the square area from the finite element model;
calculating structural stresses for the spot weld from the computed nodal forces and moments using a superposition method;
and
welding the given structure in accordance with the calculated fatigue life for the given structure.

10 more elements

A unified method for estimating fatigue for a welded structure under load, comprising:

generating a finite element model for a given structure;
calculating a distribution of structural stress within the given structure using the finite element model and while the given structure is under a given load, where the distribution of stress is determined in relation to a curvilinear plane of the given structure, such that the curvilinear plane is modeled with multiple elements of the finite element model and each element is modeled with three nodes along each element edge intersecting the given structure;
determining whether stress exceeds yield strength of material comprising the given structure;
calculating a distribution of structural strain experienced within the given structure using Hooks law in response to a determination that the stress is less than yield strength of material;
calculating a distribution of structural strain experienced within the given structure using an analytic method in response to a determination that the stress exceeds yield strength of material, where the distribution of structural strain is calculated in part from the calculated distribution of structural stress and the distribution of structural strain is defined in relation to the plane by at least two closed-form expressions which account for stress that exceeds yield strength of material;
determining whether the given structure is subject to non-proportional multiaxial load condition;
in response to a determination that the given structure is not subject to non-proportional multiaxial load condition, calculating a structural strain range using Rainflow cycle counting;
in response to a determination that the given structure is subject to non-proportional multiaxial load condition, calculating a structural strain range as a function of the non-proportional damage parameter which accounts for non-proportional loading effects between normal and in-plane shear stresses;
and
calculating a fatigue life for the given structure when placed under the given load using the structural strain range using a master E-N curve;
and
welding the given structure in accordance with the calculated fatigue life for the given structure.

9 more elements

Dependencies are inferred from the claim text.

Facts

Application: 17/825,657Filed 26 May 2022 · continuation
Priority: 18 Aug 2017
Published: US 2022/0281034 A18 Sep 2022
Granted: 16 Apr 2024
Term ends: Not estimatedThe source records don’t support an estimate.

Classification13 codes

B23K 31/02
Processes relevant to this subclass, specially adapted for particular articles or purposes, but not covered by any single one of main groups…:…
B23K 31/12
Processes relevant to this subclass, specially adapted for particular articles or purposes, but not covered by any single one of main groups…:…
G01M 5/0041
Investigating the elasticity of structures, e.g. deflection of bridges or air-craft wings: by determining deflection or stress
G06F 30/23
Design optimisation, verification or simulation: using finite element methods [FEM] or finite difference methods [FDM]

Family

Application62/547,343Us provisional application · filed 18 Aug 2017
Application16/055,485Parent of this continuation · filed 6 Aug 2018
US 2022/0281034 A1Pre-grant publication · published 8 Sep 2022
US 11,471,982 B2Parent of this continuation
US 2019/0054573 A1Published application
US 11,958,137 B2This patent

From the US filing history. Foreign family members aren’t listed.