Roof Crush Impact Analysis using Hypermesh and Radioss - BIW

Roof Crush - BIW

Import

• Car
• Impactor

Transforms

• This will require (in order)
• A 180° rotation about the global z-axis
• A 5° rotation about the axis through axis AB
• A 25° rotation about the axis through axis AC
• A translation to put point A at global ( -2145.26, 584.822, 1343.06)

Reference image ( Full Vehicle Model )

Interfaces

• Create a Type 7 contact interface between the impactor and the car
• choose an appropriate stiffness definition
• choose an appropriate minimum gap
• change the coefficient of friction to 0.2
• choose the appropriate friction penalty formulation
• Save the data from the interface to the time history file.

Gravity and boundary condition

Apply gravity to whole model but keep the suspension shock tower nodes
locked in Z.

Impactor Boundary Conditions

• The impactor assembly contains a spring attached for stability. Create a BCS
collector to fix the free end of the spring.
• Create a moving SKEW to define the direction normal to the impactor’s
face.
• Create a BCS collector to guide the master node of the impactor rigid body
so that it is free to translate normally to the face of the impactor, but is fixed
in all other DOFs.

Imposed Displacement

• Impose the velocity of the impactor starting from 0 mm/s at t = 0. The
displacement of the impactor should be 200 mm @ 200 ms.
• Avoid abrupt changes in the acceleration of the impactor.

Control Cards

• /ANALY card
• /DEF_SHELL card,
• /DEF_SOLID card, and
• /IOFLAG card
• /SPMD card
• /TITLE card

Engine File

• Use a constant nodal time step
• Print time history every 0.0001 seconds
• Solve for 200 ms
• Create an animation file every 0.005 seconds

Include selected output in animation files:

• Elemental Energy
• Elemental equivalent plastic strain
• Elemental hourglass energy
• Elemental von Mises stress
• Nodal added mass
• Turn on parallel arithmetic

Solution and Results Post Processing

• Run the model
• Plot force vs. displacement. Check that the FMVSS 216 target load of
47,000 N (= 3 * GVW) has been met.
• Plot the energy vs. time curves

Hyperview Post-Processing

One of the tests used in occupant safety analysis is a roof crush test. It is used to evaluate how a car will deform during a rollover accident. A safer car does not deform as much providing the occupant a larger survival space during this kind of accident. In this test, a plate-shaped impactor is pushed down on one side of the roof at constant (slow, quasi-static) speed. This load case challenges the solver because of large deformations, complex contact situations as well as local buckling. This model was computed successfully with the LS-DYNA R9.0.1 MPP implicit solver including dynamic effects. Last but not least, we want to acknowledge the CCSA for the baseline model.

1. Displacement

In geometry, displacement is a vector whose length is the shortest distance from the initial to the final position of a point P undergoing motion. It quantifies both the distance and direction of the net or total motion along a straight line from the initial position to the final position of the point trajectory. A displacement may be identified with the translation that maps the initial position to the final position.

A displacement may be also described as a relative position resulting from the motion, that is, as the final position x_f of a point relative to its initial position x_i. The corresponding displacement vector can be defined as the difference between the final and initial positions:

`{\displaystyle {s}={x_{\textrm {f}}-x_{\textrm {i}}}=\Delta {x}}`

2. Von Mises Stresses

The von Mises yield criterion (also known as the maximum distortion energy criterion^[1]) suggests that yielding of a ductile material begins when the second deviatoric stress invariant {\displaystyle J_{2}} reaches a critical value.^[2] It is part of plasticity theory that applies best to ductile materials, such as some metals. Prior to yield, the material response can be assumed to be of a nonlinear elastic, viscoelastic, or linear elastic behaviour.

4. Plastic Strain

The strain is a measure of the amount of deformation that occurs when an object is placed under stress. Strain rate is defined as the change in strain over the change in time. All materials will undergo some change in their dimensions when exposed to stress. The deformation caused by stress can be fully reversible or permanent, depending on the amount of stress applied. An elastic strain occurs when material under stress returns to its original dimensions once the stress is removed. A plastic strain occurs when an object has been exposed to very high levels of stress and will no longer return to its original shape after the stress is removed. In many materials, the reversal of elastic strain is instantaneous, meaning it occurs without a perceptible duration of time. Deformation that is fully recoverable, but occurs over time, is described in terms of the strain rate. Strain rate varies widely for different materials, and will often change at different temperatures and applied pressures. Steel is an example of a material that returns to its original state immediately after the stress is removed.

5. Specific Energy

Design of energy-absorbing structures is achieved in several steps, usually in a highly iterative design/calculation loop. Objectives of each design step are secured by the usage of dedicated computational tools typically different for each step. The selection of an appropriate tool for a given step depends on the complexity of the problem and availability of suitable software or other predictive techniques such as engineering formulas, empirical data or handbook - a type of information. For example, in the pre-design or pre - prototyping stages factors such as the specific energy absorption per unit length or the maximal moment capacity of a cross-section are of primary importance. In the case of typical cross-sections, such information is readily available in handbooks. In the case of more complex, real - word, members the desired parameters can be easily calculated by using specialized tools, such as CRASHCAD

Using commercial FE packages at the early stages of the design process are not justified due to the excessive modelling effort. On the other extreme, only professional FE packages such as PAM-CRASH, DYNA or RADIOSS guarantee the detailed, full crash simulation. In the intermediate stages of the design process usage of both computational tools is highly desirable and can 1 CRASH CAD is a highly interactive CAD/CAE Software based on the Superfolding Element approach introduced in the preceding sections.

Graph 1 Internal And Kinetic ENergy

Graph 2: 9900035mat_rigid 3- FZ-Z Force

Graph 3: 9900038 New RBODY 1 - FZ-Z Force

Graph 4 Interface_Impactor and Car

Conclusion

The vehicle roof with new material is complaint with the relevant standards by comparison analysis with CAE which is beneficial for weight reduction and hence to improve vehicle efficiency and satisfy requirements of vehicle manufacturers. As the results indicate usage of DP 600 reduces the impact of rollover accidents on the passengers and also reduces the weight of the vehicle hence enhancing its efficiency and safety. Using DP600 material for all the load-bearing components or parts of the vehicle can cause a drastic reduction of weight hence increasing its efficiency and also helps in reducing the amount of emission from the vehicle. The weight of the Car was reduced by 5.2kgs after changing the material to DP600and also the strength was increased which enhanced the energy absorbing capacity to withstand Impact loads. Also, Providing Better integrity for the side windows, Increasing A and B pillar strength and Providing more energy-absorbing padding in the head-strike areas can further increase the safety. In order to understand the impact of change in thickness of the same material (DP600) we carried out another iteration and found that the results changed drastically for just 0.2mm change in thickness.