Week 11 Car Crash simulation

CAR CRASH SIMULATION USING ANSYS WORKBENCH

OBJECTIVE

1. To simulate car crash for different thickness of car body,

1. Case-1: Thickness=0.3 mm.
2. Case-2: Thickness=0.7 mm.
3. Case-3: Thickness=1.5 mm.

2. To find out Total deformation and Equivalent stress developed in car body for each case and compare the results.

1. THEORY

1.1 Car Crash:

A crash simulation is a virtual recreation of a destructive crash test of a car using a computer simulation in order to examine the level of safety of the car and its occupants.

Crash simulations are used by automakers during computer-aided engineering (CAE) analysis for crashworthiness in the computer-aided design (CAD) process of modelling new cars. During a crash simulation, the kinetic energy, or energy of motion, that a vehicle has before the impact is transformed into deformation energy, mostly by plastic deformation (plasticity) of the car body material (Body in White), at the end of the impact.

Data obtained from a crash simulation indicate the capability of the car body to protect the vehicle occupants during a collision against injury. Important results are the of the occupant space (driver, passengers) and the decelerations felt by them, which must fall below threshold values fixed in legal car safety regulations. To model real crash tests, today's crash simulations include virtual models of crash test dummies and of passive safety devices (seat belts, airbags, shock absorbing dash boards, etc.). Guide rail tests evaluate vehicle deceleration and rollover potential, as well as penetration of the barrier by vehicle.

Crash simulations are used to investigate the safety of the car occupants during impact on the front-end structure of the car in a frontal impact, the lateral structure of the car in a side collision, the rear end structure of a car in a rear impact.

Fig. 1.1 Front end crash of car body and wall.

In this project a car body is crashed against the wall. The wall is made to displace 500 mm, such that is gets crashed into the front portion of the car body and deforming the impacted region of the car body. A parametric study is carried out for different thickness of car body, i.e., 0.3 mm, 0.7 mm and 1.5 mm. The results of total deformation and equivalent stress for different cases of car body thickness is compared and analysed.

2. ANALYSIS SETUP

2.1 Geometry:

Fig.2.1 3D model of car body and wall.

The given 3D model of car body and wall is imported into SpaceClaim. The different thickness assigned for car body are as follows,

1. Case-1: Thickness=0.3 mm.
2. Case-2: Thickness=0.7 mm.
3. Case-3: Thickness=1.5 mm.

Note: The analysis setup of only case-1 is demonstrated.

2.2 Material Properties:

a. Stainless Steel NL.

b. Structural Steel.

Fig.2.2 Material property details of car body and wall.

The material assigned for car body is stainless steel NL and for wall, structural steel.

2.3 Symmetry Region:

Fig.2.3 Symmetry region of car body and wall.

The given model is symmetric, hence only half portion of car body and wall is considered for analysis to save computational time.

2.4 Meshing:

a. Patch conforming method. 

b. Face sizing of rear portion of car body.

c. Meshed model

Fig.2.4 Meshing details of car body and wall.

The elements of wall is set to tetrahedrons using patch conforming method. The element size of rear end portion of car body is set to 170 mm using face sizing option. The total number of nodes and elements generated are 11389 and 13610 respectively.

Note: The academic version of software has the problem size limit of 128k nodes or elements.

2.5 Boundary Conditions:

2.5.1 Analysis settings:

Fig.2.5.1 Analysis settings.

In the analysis settings the number of steps considered is 1. The end time specified is 1e-003. The maximum no. of cycles is 1e+07. The maximum energy error is 0.1. The initial, minimum and maximum time step is set to ‘Program Controlled’.

2.5.2 Boundary condition for wall hitting car body:

a. Fixed support.

b. Displacement applied to wall along z-axis.

Fig.2.5.2 Boundary conditions for wall hitting car body.

The rear end surface of the car body is fixed. The wall is directed to hit the front portion of the car body with a displacement of 500 mm in z-direction.

3. RESULTS AND DISCUSSIONS

3.1 Case-1: Thickness=0.3 mm.

a. Total Deformation.   

b. Equivalent (v-m) Stress.

3.2 Case-2: Thickness=0.7 mm.

a. Total Deformation.                                                

b. Equivalent (v-m) Stress.

3.3 Case-3: Thickness=1.5 mm.

a. Total Deformation.                                                

b. Equivalent (v-m) Stress.

3.4 Comparison of Results:

From the table, it is observed that the maximum total deformation for case-1 is 1052.7 mm which is more compared to case-2 and case-3. The thickness of car body for case-1 is 0.3 mm, hence it gets deformed easily compared to other cases.

The v-m stress developed for case-1 is 3581.9 mm which is maximum compared to other cases, because the stiffness is less and the impact force absorbed in case-1 is more compared to other cases.

4. ANIMATION OF RESULTS:

4.1 Case-1: Thickness=0.3 mm.

a. Total Deformation.

b. Equivalent (v-m) Stress.

4.2 Case-2: Thickness=0.7 mm.

a. Total Deformation.

b. Equivalent (v-m) Stress.

4.3 Case-3: Thickness=1.5 mm.

a. Total Deformation.

b. Equivalent (v-m) Stress.

CONCLUSION

Simulation of car body crashing the wall was carried out successfully for the following cases of car body thickness,

1. Case-1: Thickness=0.3 mm.
2. Case-2: Thickness=0.7 mm.
3. Case-3: Thickness=1.5 mm.

The maximum total deformation for case-1 was more compared to case-2 and case-3.

The v-m stress developed for case-1 was maximum compared to other cases.

From the weight reduction point of view case-1 is preferred, whereas, from the safety point of view case-3 is preferred.