Spot Weld Failure Criterion for Solid-Element Finite Element Models
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Solution Overview
Problem
Current finite element analysis methods for simulating spot welds in structures, such as cars, are inadequate as they fail to accurately model spot weld failure, especially when using solid elements, leading to inconsistent results with traditional material failure methods.
Innovation Solution
The method represents each spot weld as a cluster of solid elements, allowing for arbitrary tie-connection between shell elements and incorporates a failure criterion that considers shear and axial stresses, location sensitivity, and strain rate effects to determine spot weld failure, particularly in 'plug rupture' mode.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Ease of manufacture
If spot welds are modeled using beam elements, then the model creation effort is reduced, but the modeling accuracy becomes inadequate when element size is smaller than spot weld diameter
Solution Approach 1:
The spot weld is segmented into multiple solid elements arranged in a cluster configuration, allowing the weld to be represented with sufficient geometric detail while maintaining computational efficiency. This segmentation enables accurate representation of the weld geometry even when surrounding element sizes are smaller than the weld diameter.
Solution Approach 2:
The spot weld is represented as a nested cluster of solid elements within the larger finite element model. This nested structure allows the weld to contain multiple internal elements that collectively represent the weld geometry, while the entire cluster fits within the broader structural model hierarchy.
2Reliability
If traditional material failure method is used for solid elements, then the failure determination is consistent with solid element theory, but the spot weld failure determination becomes inconsistent with beam element methods
Solution Approach 1:
The failure determination method is designed to be universal, working consistently for both beam element and solid element models of spot welds. The criterion evaluates stresses and strains in a manner that adapts to different element types, providing a unified approach to failure prediction across various modeling methodologies.
Solution Approach 2:
The failure criterion incorporates parameter adjustments that account for the differences between beam and solid element representations. By modifying the evaluation parameters based on element type and geometry, the method maintains consistency in failure determination while adapting to the specific characteristics of each element formulation.
3Measurement precision
If spot welds are modeled with multiple solid elements, then the geometric representation is improved, but the failure criterion development becomes more complex
Solution Approach 1:
The stress and strain results from multiple solid elements within the spot weld cluster are merged and combined into a unified failure evaluation. This aggregation approach simplifies the failure criterion by consolidating the contributions of individual elements into a collective assessment, reducing the complexity of evaluating multi-element configurations.
Solution Approach 2:
The failure criterion utilizes a standardized evaluation approach that can be copied and applied consistently across different spot weld configurations. By establishing a template methodology for assessing multi-element clusters, the complexity of developing unique criteria for each configuration is reduced through repetition of a proven evaluation framework.
Data Source
AI summary
Each spot weld in a structure is represented by a cluster of at least one solid element in a finite element analysis model of the structure. Each spot weld is used for tying together two parts. Each of the two parts are generally represented or modeled as a number of two-dimension shell elements. Since the tie-connection between the spot weld and the two parts can be located arbitrarily within the respective part, the shell elements representing the two parts do not have to be aligned in space. The only requirement is the two shell elements must be overlapped each other such that the spot weld can tie the two shell elements (i.e., one from each part) together. A spot weld failure criterion used for determining failure including shear and axial stresses acted on the spot weld, shell element size and spot weld location sensitivity scale factors and strain rate effect.