Self-Contact
Self-Contact: Theoretical Foundations
What is Self-Contact?
Professor, is self-contact a problem where a structure contacts "itself"?
Yes. It's a problem where a part of a structure contacts another part due to large deformation. Examples include rubber O-ring compression, sheet metal bending, tire deformation, balloon inflation, etc.
Normal contact is between "two separate bodies," but self-contact is between "different surfaces of the same body." Contact detection is complex.
Settings in FEM
Summary
Key Points:
- A structure contacts itself — Occurs in large deformation
- Contact detection is complex — Monitoring distances between surfaces within the same body
- General Contact (automatic contact) is convenient — Self-contact is also automatically detected
Mathematical Definition of Self-Contact
Self-contact is a phenomenon where different parts of a single object come into contact with each other. It has a higher degree of freedom in deformation compared to normal contact problems and is characterized by the inability to identify contact pairs in advance. Mathematically, it is formulated as a condition where the mapping φ on the initial configuration Ω ceases to be injective. In 1987, Ciarlet & Nečas proved the existence theorem for "deformations without self-intersection" in Sobolev spaces.
Computational Methods for Self-Contact
Implementation of Self-Contact
```
*CONTACT, TYPE=GENERAL CONTACT
*CONTACT INCLUSIONS, ALL EXTERIOR
```
General Contact + ALL EXTERIOR automatically detects self-contact on all exterior surfaces.
```
*CONTACT_AUTOMATIC_SINGLE_SURFACE
1 $ Part set ID
```
Summary
High-Speed Search via Bucket Sort
The bottleneck in self-contact detection is the O(N²) exhaustive pair search. The bucket sort (spatial hashing) method implemented in LS-DYNA Version 930 (around 1993) divides the computational domain into cells and only considers nodes within the same or adjacent cells as pair candidates, reducing computational complexity to O(N logN). Even today, adaptive bucket sizes combined with GPU parallelization form the backbone of mainstream algorithms.
Self-Contact in Practice
Self-Contact in Practice
Practical Checklist
Automotive Door Crash Analysis
In the late 1990s, during the crash test reproduction analysis for the Ford Explorer door, self-contact occurred when the inner trim panel folded. Analyses that did not consider this showed intrusion amounts more than double the measured values. Models applying LS-DYNA's SINGLE_SURFACE contact reported intrusion errors within ±8%, enabling door beam shape optimization without physical experiments, as documented in SAE Paper 1999-01-3155.
Self-Contact: Software & Solver Comparison
Self-Contact Tools
Selection Guide
Evolution of LS-DYNA Self-Contact
LS-DYNA3D's self-contact feature was first published by John Hallquist in a 1987 LLNL internal report. Initially called SINGLE_SURFACE contact, it specialized in folding thin-shell structures. Version 940 (1994) added segment-based self-contact, enabling compression of thick objects. The current R14 version implements asynchronous bucket reconstruction for MPPP (Massively Parallel Processing), making self-contact analysis on a scale of 1 billion elements practical.