Bolt Pretension Initialization in Finite Element Analysis
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Solution Overview
Problem
Existing finite element analysis methods for simulating bolted joints are cumbersome and inaccurate, particularly in initializing bolt pretension, as they often require specifying axial strain or detailed bolt models, which can lead to inconsistent pretension across multiple bolts with different orientations.
Innovation Solution
A method that numerically initializes bolt pretension using a pretension-versus-time curve with a ramp and desired pretension portion, allowing for quasi-static analyses to apply and terminate pretension independently of axial strain, ensuring consistent pretension across bolts without iterative axial strain determination.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Measurement precision
If prior art methods specify axial stretch or use thermal gradient to create bolt pretension, then pretension can be applied to bolts, but the interactions between multiple bolts in close proximity result in inaccurate pretension for many bolts
Solution Approach 1:
The patent segments the bolt pretension application process by treating each bolt independently through individual beam elements with separate pretension specifications. This allows each bolt to be initialized with its desired pretension value without being affected by interactions with neighboring bolts, thereby achieving accurate pretension for all bolts simultaneously while maintaining a relatively simple beam element model.
Solution Approach 2:
The patent applies preliminary action by initializing bolt pretension at the beginning of the analysis before any structural responses occur. The pretension is applied as an initial condition to beam elements representing bolts, ensuring that all bolts achieve their desired pretension levels before the actual structural analysis begins, avoiding the need for complex iterative adjustments during the analysis.
2Measurement precision
If detailed bolt models with multiple solid elements are used to ensure pretension as internal stress, then accurate pretension can be achieved, but the model complexity and computational cost increase significantly
Solution Approach 1:
The patent uses beam elements as simplified copies or representations of actual bolts, capturing the essential pretension behavior without modeling the complete geometric and structural complexity of real bolts. This beam element abstraction maintains accuracy for pretension analysis while dramatically reducing model complexity compared to detailed solid element models.
Solution Approach 2:
The patent changes the modeling parameter from detailed geometric representation (solid elements) to a simplified structural representation (beam elements) that focuses on the critical parameter of pretension. This parameter change allows the model to capture the essential mechanics of bolt pretension without the computational burden of detailed bolt geometry.
3Measurement precision
If iterative determination of axial strain is performed to achieve desired axial stress in bolts, then accurate pretension can be achieved, but the process becomes cumbersome and time-consuming
Solution Approach 1:
The patent applies preliminary action by directly specifying the desired pretension values as initial conditions for beam elements before the analysis begins. This eliminates the need for iterative determination of axial strain during the analysis, as the pretension is already established in the initial configuration, significantly reducing the time required for model initialization.
Data Source
AI summary
In one aspect of the invention, each bolt is modeled using a beam element in a FEA model. To apply desired pretension to one or more bolts, at least one pretension-versus-time curve is specified. Each pretension-versus-time curve includes ramp portion, desired pretension portion and optional unloading portion. Duration of the pretension-versus-time curve generally covers first 0.5-1% of total simulation time of a car crashworthiness analysis. Ramp portion starts from zero to desired pretension in a substantially linear manner, and hence being configured for applying desired pretension to a bolt gradually with smaller increments. Desired pretension portion is configured for ensuring the desired pretension can actually be applied to the beam element during an initialization process - a series of quasi-static analyses. Since the method is independent of the deformation of the beam, the method completely avoids the need to iteratively determine an axial strain or displacement that gives the desired pretension.