Week 11 Car Crash simulation

CAR CRASH SIMULATION USING ANSYS WORKBENCH:

AIM:

To study and perform explicit dynamic analysis for car crash simulation. There will be three different analyses on the same model with varying type of thickness and get results for Equivalent stress and the total deformation in the model and grid dependency test was also performed to optimize the element size for better accuracy.

Case 1 : Thickness 0.5 mm for Car Body

Case 2: Thickness 2 mm for Car Body

Case 2: Thickness 5 mm for Car Body

DYNAMIC ANALYSIS SETUP FOR CAR CRASH SIMULATION OPERATION:

I. GEOMETRY:

The CAD model of explicit analysis model is imported in Ansys dynamic environment. Then, the model is generated and checked if any abnormalities are present in the model. It is a highly non-linear transient dynamics phenomenon. The purpose of a crash analysis is to see how the car will behave in a frontal or sideways collision. Crashworthiness simulation is one typical area of application of Finite-Element Analysis (FEA). This is an area in which non-linear Finite element simulations are particularly effective. It is based on the principle of the vehicle's structural ability to plastically deform and yet maintain a sufficient survival space for its occupants in crashes involving reasonable deceleration loads. Restraint systems and occupant packaging can provide additional protection to reduce severe injuries and fatalities.

II. MATERIALS:

Below are the materials which is used to perform analysis for the dynamic analysis of model. The analysis is carried out for given material individually.

Car Body: Stainless Steel NL

Wall: Structural Steel

The details of each material has been carried out below as shown in the image:

III. CONNECTION DETAILS:

Body interactions:

In this type, all bodies are selected as its interaction part as its geometric selection part. As, its definition type is frictionless.

IV. MESH:

• Basically, we have preferred default mesh for whole setup.
• As, we have to do face sizing for the critical part, hence we have selected 9 faces as critical part and given element size of 175 mm.
• Also, we have add patch conforming method to cutting tool as its geometric selection and defined its method as tetrahedrons.
• Likewise, we have selected car body as its geometric selection part and defined the method as 'Traingles.'
• Likethat, we have generated the fine mesh which is sufficient to carrry out simulation which gives desired results.

V. Symmetry:

• As, we have selected 1 face of wall as its geometric selection and it's symmetric to X-axis to the global coordinate system.
• For same, we have selected 7 edges for the car body as its geometric selection part and it's symmetric to X-axis to the global coordinate system.

VI. ANALYSIS SETTINGS AND BOUNDARY CONDITIONS:

A. ANALYSIS SETTINGS:

For this analysis the number of steps is set to 1 with maximum number of cycles is 1e+07 and end time is 1e-3 and it is defined by time, hence initial, maximum and minimum time will be program controlled. As, maximum energy error would be 5.

B. BOUNDARY CONDITIONS:

1. Fixed Support:

Basically, we have to fix the part so to analyze the results. Therefore, we have fixed the 8 faces of car body as its geometric selection and we have selected it as fixed type support.

2. Displacement:

As, we have to select the 1 face of wall as its geometric selection part. Then its type is specified by displacement and its coordinate system is defined by 'Global coordinate system'. Then, its Y and Z component gets value as constant and Z component value gets linear direction displacement in tabular form.

VI. POST-PROCESSING RESULTS:

Now, we have to compare the deformation and stress on the basis of different materials. Then, we have to analyze the result for total deformation, equivalent stress for dynamic analysis for operation. The results are as shown below:

I. Case 1_Thickness 0.5 mm:

A. Total Deformation:

• Here, the maximum deformation is 296.2 mm.
• Though we have given the displacement to the wall up to 500 mm, we can see the deformation is occuring up to 1183 mm.
• Due to collision, bumper portion is experiencing the maximum deformation; this is because it is in the initial contact to the wall.
• Due to impact of the wall, frontal portion is facing the plastic deformation as we can observe the tearing of the frontal surface due to deformation.

B. Equivalent Stress:

• Here maximum stress is 722.49 MPa.
• Due to collision of the Car Body to the wall, we can see the maximum stress is occuring at the wall.

II. Case 2_Thickness 2 mm:

A. Total Deformation:

• Here the maximum deformation is 214.64 mm
• Due to impact of the wall, frontal portion is facing the plastic deformation.
• So, we can observe the maximum deformation is occuring on frontal portion of the car body.

B. Equivalent Stress:

• Here maximum stress is 1132.8 MPa.
• Due to collision of the Car Body to the wall, we can see the maximum stress is occuring at the wall.
• Here, the thickness of car body is increased up to 2 mm, so the location of the maximum stress is different but also on the wall.

III. Case 3_Thickness 5 mm:

A. Total Deformation:

• Here the maximum deformation is 529.31 mm
• Due to impact of the wall, frontal portion is facing the plastic deformation.
• So, we can observe the maximum deformation is occuring on frontal portion of the car body.

B. Equivalent Stress:

• Here maximum stress is 1125.2 MPa.
• Due to collision of the Car Body to the wall, we can see the maximum stress is occuring at the wall.
• Here, the thickness of car body is increased up to 5 mm, so the location of the maximum stress is different but also on the wall.

VII. POST-PROCESSING RESULTS:

Parameters	Case 1	Case 2	Case 3
Maximum Total Deformation	296.2 mm	214.64 mm	529.31 mm
Minimum Total Deformation	0	0	0
Maximum Equivalent stress	722.49 MPa	1132.8 MPa	1125.2 MPa
Minimum Equivalent stress	0	0	0

• On comparision of the three cases, we can see the stress is high for the Case_2, where the thickness of the car body is 2 mm.
• Also, the deformation is high for 5 mm thickness, because it can deform easily.
• In Case_2, where the thickness is 2 mm, stress and deformation decreases compare to Case_1
• Lowest stress and deformation is resulting in Case_1 and Case_2, where the thickness is 0.5 mm and 2 mm, because it can resist more to the load or given displacement.

CONCLUSION:

• From the above results, we can conclude that the stress and deformation is decreasing as increase in thickness of the Car Body.
• With 0.5 mm thickness, the car body will be very light in weight, and can accelerate high, so all the energy will be dissipated to the Car body and the damage will also be high.
• With 5 mm thickness, it will be little rigid. So it will not dissipate more energy and the energy will be transfered to whole car body, which is also not good.
• With thickness of 2 mm, the car body will not be so rigid and also not accelerate more, so energy absorption will be optimized.
• So, 2 mm thickness is prefered for the car body for good crash safety results.
• Further study can be taken with different material properties for frontal impact with the same thickness to verify effect of material yeild, plasticity on force carrying capacity, energy absorption and acceleration levels.