Finite Element Fastener Modeling via Fence Elements
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Solution Overview
Problem
Finite element modeling of fastener holes in plates is a trade-off between accuracy and computation time, with detailed models providing accurate results but requiring excessive time, while simplified models reduce computation time but often inaccurately represent interactions between fasteners and hole edges.
Innovation Solution
A simplified finite element model is developed using plate fence elements with high stiffness parallel to hole axes and low stiffness perpendicular to them, along with bolt disk models and beam elements to accurately represent bolt bearing stiffness, reducing computation time while maintaining accuracy.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Measurement precision
If detailed finite element models are used to model fasteners in detail, then accuracy of stress results is improved, but computation time increases excessively
Solution Approach 1:
The fastener is segmented into distinct functional components: bolt head modeled as a rigid body, shank as a beam element, and washer as a separate rigid body. This segmentation allows each component to be modeled with appropriate complexity - the rigid bodies capture contact interactions accurately while the beam element efficiently represents the shank's structural behavior, resolving the contradiction between accuracy and computation time
Solution Approach 2:
Different levels of modeling detail are applied to different parts of the fastener system. The bolt head and washer use rigid body elements with contact formulations to accurately capture local stress interactions at critical interfaces, while the shank uses simplified beam elements. This local differentiation maintains accuracy where needed while reducing overall computational complexity
2Loss of time
If simplified finite element models are used to reduce computation time, then computation time is reduced to acceptable times, but accuracy of computed stresses proximate to fastener holes deteriorates
Solution Approach 1:
Contact elements are introduced as intermediary components between the rigid bolt head/washer bodies and the plate elements. These contact elements mediate the stress transfer and accurately capture the complex interaction mechanics at the fastener-plate interface, ensuring accurate stress results proximate to fastener holes while maintaining the simplified rigid body modeling approach
Solution Approach 2:
The model uses parameter changes to transition between different modeling approaches - rigid body formulation for the bolt head and washer to capture contact behavior, beam elements for the shank to represent structural properties, and appropriate material property assignments. These parameter choices enable accurate stress computation while maintaining computational efficiency
3Loss of time
If simplified models are used to model fastener holes, then computation time is reduced, but the models fail to accurately represent interactions between fasteners and edges of fastener holes
Solution Approach 1:
Contact elements serve as intermediaries that accurately represent the interaction between the rigid fastener components and the plate material around the fastener holes. These contact formulations capture the complex mechanical interactions including bearing stresses and potential separation, ensuring reliable representation of fastener-plate interactions while maintaining the computational efficiency of the simplified model
Data Source
AI summary
Method and computer program product for generating a finite element model of a fastener passing through holes in load-bearing plates. Disks of finite elements are arranged in the holes to model the portions of the fastener aligned with each hole. Fence elements extend about the perimeters of the disks and the perimeters of the holes in directions away from sides of the disks and load-bearing plates. Contact bodies can be arranged on the fence elements. When a finite element model is executed, the fence elements and contact bodies can bear against each other to model contact between the holes and the fastener.