Formed Steel Component Assessment for Sheared-End Delayed Fracture
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Solution Overview
Problem
Existing methods for assessing delayed fracture characteristics in sheared end surfaces of high-strength steel sheets, particularly those with tensile strengths of 980 MPa or more, fail to accurately predict fracture occurrence under actual automotive component conditions due to deviations from deformation states and neglect changes in fracture characteristics by plastic deformation.
Innovation Solution
A method for assessing delayed fracture characteristics in formed components by determining a stress margin using a test piece subjected to a predetermined load stress and hydrogen entry environment, followed by forming analysis to calculate residual stress and load stress, allowing for accurate prediction of fracture risk based on stress margin.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Ease of manufacture
If conventional assessment methods (PTL 1-3) are used to evaluate delayed fracture characteristics, then the assessment process is simplified, but the assessment accuracy fails to reflect actual component conditions due to deviation from real deformation states and neglect of plastic deformation effects
Solution Approach 1:
The invention applies preliminary plastic deformation to the test piece before conducting the delayed fracture assessment. By pre-applying forming strains (tensile or compressive) that simulate actual component deformation states, the test piece is prepared in advance to reflect real service conditions. This preliminary action ensures that the assessment accurately predicts delayed fracture behavior in actual automotive components while maintaining a systematic evaluation process.
Solution Approach 2:
The invention changes the strain state parameter of the test piece by applying controlled tensile or compressive forming strains before assessment. This parameter modification allows the test to simulate different actual component conditions (such as press forming operations), thereby improving assessment accuracy without significantly complicating the overall process. The strain amount is controlled within specific ranges to achieve realistic deformation states.
2Strength
If high-strength steel sheets with tensile strength of 980 MPa or more are used to reduce vehicle weight and improve collision safety, then vehicle fuel consumption is improved and passenger protection is enhanced, but delayed fracture occurs more frequently in sheared end surfaces
Solution Approach 1:
The invention applies preliminary forming strains to test pieces made from high-strength steel sheets before conducting delayed fracture assessment. By pre-deforming the material in controlled tensile or compressive strains that simulate actual press forming operations, the test captures how high-strength steels behave under realistic service conditions. This allows accurate prediction of delayed fracture risks in components made from these high-strength materials, enabling their safe use for weight reduction while maintaining reliability.
Solution Approach 2:
The invention focuses assessment on the sheared end surface region, applying localized forming strains that simulate actual component deformation. By concentrating the evaluation on this critical region where delayed fracture most commonly occurs in high-strength steels, the method provides targeted reliability assessment for the most vulnerable area while allowing the rest of the component to utilize the full strength potential of the high-strength steel.
3Device complexity
If the sheared end surface is placed in hydrogen entry environment under no load with as-sheared condition, then the test setup is simplified, but the assessment fails to predict delayed fracture that occurs under actual service loads
Solution Approach 1:
The invention applies preliminary forming strains and controlled loading conditions before placing the test piece in the hydrogen entry environment. This preliminary preparation includes applying tensile or compressive strains that simulate actual service loads, ensuring that the assessment reflects real-world conditions. The load is maintained during hydrogen exposure to capture the interaction between mechanical stress and hydrogen embrittlement, improving prediction accuracy without excessive complexity.
Solution Approach 2:
The invention modifies the stress state parameter by applying controlled loads during the hydrogen entry test, rather than testing under zero load. The load level and type (tensile or compressive) are adjusted to match actual service conditions. This parameter change enables the test to predict delayed fracture under realistic service loads while maintaining a systematic and controllable test procedure.
Applied Scientific Principles
This section explains which scientific principles are used to turn an abstract innovation direction into a practical engineering solution.
Function Achieved in This Case
Enables more accurate assessment of delayed fracture risk in sheared end surfaces, facilitating the manufacture of components that suppress fracture and expanding the use of ultrahigh-strength steel sheets in automotive applications.
Implementation Method 1
placing the metal sheet for a predetermined time in a predetermined hydrogen entry environment
Data Source
AI summary
A method for manufacturing a formed component includes: determining a stress margin with a strain amount as a variable based on results of a test including placing a metal sheet in a predetermined hydrogen entry environment in a state where a load stress is loaded to a sheared surface of the metal sheet and the metal sheet is restrained; performing forming analysis of forming the metal sheet into the formed component and determining a residual stress and the amount of strain in a sheared end surface of the formed component; determining a load stress to be loaded to the sheared end surface by assembling the formed component to another component; and assessing a margin of the delayed fracture in the formed component based on the stress margin corresponding to the determined amount of strain and a total stress of the determined residual stress and the determined load stress.