1. How to Perform Analysis Utilizing Large Deformation of Structures?

Today's topic is the "large deformation" behavior of structures.

In everyday life, situations involving the transfer of forces of varying magnitudes occur frequently.
Automobile collisions are one of the most representative cases where extremely large forces are applied, and it is easy to observe that the faster the speed, the more severe the vehicle damage becomes.

In large deformation behavior such as crushing, the effect of absorbing energy against large externally applied forces can be achieved.
Spring structures such as suspensions also utilize large deformation to reduce impact forces, and this principle is reflected in various designs.

 

2. Why Is It Necessary to Account for The Energy Absorption Effect Due to Deformation in Structural Design?

In everyday life, situations involving applying or receiving forces of varying magnitudes frequently arise. These range from a light tap of the hand, to being struck by a flying object, or even a vehicle collision in more severe cases. When colliding with an object, we naturally respond by moving in the direction of impact to gradually absorb the force, or by falling and dispersing it through breakfall techniques. So how does this apply to structures?

In structural design, allowing the structure to deform sufficiently under external forces plays the role of dissipating energy. For extremely large forces such as those in vehicle collisions, designs are also made to increase energy absorption through large deformation utilizing plastic deformation of the material. In fact, it is said that the core engineering capability lies in designing the vehicle so that occupants can safely survive even when the vehicle is crushed to the point of being half-destroyed in a rear-end collision.

Utilizing these phenomena, experiments or CAE analyses are conducted for the purpose of verifying the energy absorption of a structural design and deriving the optimal configuration suited to objectives such as overturning prevention and safety.

3. How Can Large Deformation Behavior Be Approached Analytically?

Since CAE analysis builds a model in an idealized virtual space and expresses deformation results relative to user-defined conditions, it must be applied with great care. When incorporating large deformation behavior of structures into CAE analysis, nonlinearity is taken into account. Geometric nonlinearity is evaluated based on a bending deformation threshold of 15 degrees or more, and the accompanying plastic deformation of the material and contact separation phenomena are additionally considered.

This analysis example simulates the ROPS (Roll Over Protective Structure) test for a tractor body frame, with the objective of verifying the energy absorption under geometric and material nonlinearity while considering lateral and rear loading. The aim is to briefly examine the verification results using a simple model composed of 2D Shell + 3D Solid elements, as well as the differences arising from different material curves.

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