Frontal Crash Test Analysis on Neon BIW (Body in White) using Crashworthiness and RADIOSS

Objective : To Perform the frontal Crash Impact on the given BIW Model and to Study the impact of the crash using Hyper crash & Radioss.

1) Introduction :

A crash simulation is a virtual recreation of a destructive crash test of a vehicle using a computer simulation in order to examine the level of safety of the vehicle and its occupants. Data obtained from a crash simulation indicate the capability of the vehicle body to protect the vehicle occupants during a collision against injury. This simulation technology have greatly increased the protection, dependability and producing potency in today’s vehicles. The advantage of the simulation are numerous and important. Computer aided parametric design software will be used for modelling of the problem to define all the coordinate values and geometrical details, then this CAD data would be transferred to an FEM software for pre-processing, solution and post-processing followed by generation and
interpretation of results related to energies, acceleration and displacements with different loads & boundary conditions possible in various accidental situations. Automotive industry has probably the widest application of crash simulation. Simulating the crashworthiness of the vehicle in terms of very simple models based on the spring mass damper systems was the focus when the computers were very slow and the breakthrough occurred when LSTC was formed. Nowadays software such as LS DYNA and others have very wide practical aspects by incorporating special seat belt elements and passenger dummies for simulating precisely the occupant safety under various crash situations. Several standards have been originated in various countries related to automobile crashing. Although developed mainly for automotive applications, crash simulation software’s have also found application in train, ship and aircraft crashworthiness. The two main standards associated with FAA (Federal Aviation Administration) requirements are those of bird strike impact and engine blade containment. Other applications in defence sector are simulating the explosive detonation process and design of weapons. Computational Biomechanics also is continuously evolving with the development of finite element models closely following the actual physics models.

Finite Element Analysis :

Simulation using finite element method comprises of three major phases:

(i) pre-processing

In which the analyst develops a finite element mesh to divide the subject geometry into sub-domains for mathematical analysis,and applies material properties and boundary conditions.

(ii) solution

During which the program derives the governing matrix equations from the model and solves for the primary quantities.

(iii) post-processing

In which the analyst checks the validity of the solution, examines the values of primary quantities (such as displacements and stresses), derives and examines additional quantities (such as specialized stresses and error indicators).

Crash Test :

A crash test is a form of destructive testing usually performed in order to ensure safe design standards in crashworthiness and crash compatibility for various types of vehicle like small, medium and heavy duty and its related systems and components for the sake of getting the performance of the vehicle under the different conditions of crash at different angles with taking certain object like rigid wall, cables specially three-strand cable, concrete barriers, guardrail systems etc. It will be performed either by numerical simulations or experimentally. depicts different types of crash test generally used.

Frontal Impact test:

In this test a fully front structure of the vehicle collides with another object like another vehicle, rigid wall etc. at a given speed.

Crashworthiness Restrain Technologies:

Software Used For this Crash test :

Hyperworks is the leading CAE integration platform for crash and safety design. It covers all the different steps from meshing to optimization including:

• Vehicle modeling and assembly using Hypermesh
• Analysis setup - including model checking, dummy positioning, airbag folding using Hypercrash
• Crash analysis using RADIOSS
• Visualization - results analysis and report automation using Hyperview
• Study and optimization using Hyperstudy and Optistruct
• LS DYNA is another software for crash test.
• Simple crash tests can also be simulated using ANSYA WORKBENCH.

Implicit and Explicit Philosophy :

Most software’s would normally solve the dynamic equilibrium equation in an implicit approach however the foremost widespread approach that ought to be used for highly non-linear issues is to use explicit(specific) time integration scheme like a central difference scheme. There are several benefits of such a procedure and therefore the most significant is that it results in an algorithmic programmed which may be simplified programmed, does not need any matrix operation procedure and more is very appropriate for a quick parallel computing methodology.

Common Element used in Crash FE Analysis :

• Shell element- Quadrilateral, Triangular, Belytschko-Lin-Tsay shell element
  
• Beam element- Hughes-Liu beam element
  
• Hexahedron element
  
• Solid element

Common Material used in Crash FE Analysis :
These are some material found in the literature survey which is generally used in crash analysis of automobile components which is shown through.

Typical Issues in Contact Analysis :

Some contact conditions which are given at the time of crash analysis are given below:-

• Contact with rigid walls
  
• Contact with two bodies
  
• Folding of some shell parts of the car body on itself.
  
• Other multiple contact

Contact between the two components occurs when they try to come towards each other during the deformation process. But at the time of contact some of the issues are playing major roles which are given below:-

• Improper surface normal
• Compatible elements
• Boundary conditions
• Extending the rigid surface
• Mesh density of slave surface
• Proper selection of master & slave
• No initial penetration
• Avoid sharp corner

Impact Objects and Conditions :

The conditions and object which are used at the time of impact are given below:-

• Rigid wall
  
• Flexible walls
  
• Barriers
  
• Arbitrary impact angles
  
• Head-to-Head collision
  
• Rollover impact
  
• Multiple vehicle collision (car-to-car, car-to-motorcycle) and so forth.

Physics of a Crash:

During a car crash, energy is transferred from the vehicle to whatever it hits, be it another vehicle or a stationary object. This transfer of energy, depending on variables that alter states of motion, can cause injuries and damage cars and property. The object that was struck will either absorb the energy thrust upon it or possibly transfer that energy back to the vehicle that struck it. Focusing on the distinction between force and energy can help explain the physics involved.

2) PROCEDURE :

Unit Systems :

The Unit system given in the rad file are in the form of kg mm ms which can be seen in the below figure.

Interface:

A proper New Interface is created with the recommended parameters which will be seen in the below figure.

The above higlighted boxes are the recommended parameters for the particular interface created.

Review of Interface:

In this case as we have created a new interface the whole body of the BIW will be the master nodes and the slave nodes.

Review of Axial Load Interface:

In this case from the above figure for the axial load the bumper of the car will be the master nodes which is in blue in colour and the rail component which is in connection with the bumper will be the slave nodes which is in the red colour.

Penetrations and Intersections:

There was no penetrations observed as we have given the In_acti value as 6 where the gap is the variable with the time but the initial penetration is completed.

Rigid Bodies:

A rigid body is created by selecting the centre most point of the element to oppose the force in it's direction.

Review of the Dsearch :

CENTER OF GRAVITY:

Center of gravity, also known as center of mass, is that point at which a system or body behaves as if all its mass were centered at that point. Where the weight, and also all accelerative forces of acceleration, braking and cornering act through it.

• Center of gravity location can be defined as:
  
• The balance point of an object
  
• The point through which a force will cause pure translation
  
• The point about which gravity moments are balanced
  
• The point which if the body is hanged from it will stay balanced (leveled as it is on the ground).

What is the importance of the CG ?
When making an analysis of the forces applied on the car, the CG is the point to place the car weight, and the centrifugal forces when the car is turning or when accelerating or decelerating. Any force that acts through the CG has no tendency to make the car rotate.

The center of mass height, relative to the track, determines load transfer, (related to, but not exactly weight transfer), from side to side and causes body lean. When tyres of a vehicle provide a centripetal force to pull it around a turn, the momentum of the vehicle actuates load transfer in a direction going from the vehicle's current position to a point on a path tangent to the vehicle's path. This load transfer presents itself in the form of body lean. Body lean can be controlled by lowering the center of weight or the widening the car track, it can also be controlled by the springs, anti-roll bars or the roll center heights.

The center of mass height, relative to the wheel base, determines load transfer between front and rear. The car's momentum acts at its center of mass to tilt the car forward or backward, respectively during braking and acceleration. Since it is only the downward force that changes and not the location of the center of mass, the effect on over/under steer is opposite to that of an actual change in the center of mass.

A lower center of mass is a principal performance advantage of sports cars, compared to sedans and (especially) SUVs. Some cars have body panels made of lightweight materials partly for this reason.

CG and MASS Balance Equivalent to Neon:

The weight of the Neon is of 700 kg. To meet the parameters of this neon we add additional mass to the given model to form the CG and meet it's quality criteria.

From the above figure we can figure out that the Total mass of the body is of 700 kg and the centre of gravity is in between by balanceing the mass on both the sides. Hence we can say that the CG is at the required range.

Initial Velocity:

The given initial velocity was of 35 mph. Here in this case we convert this value by using the consistent units. As our units are in Kgs the consistent value of 35 mph is 15.65 which we can see in the above highlighted figure.

Sectional forces:

The Sectional forces are applied on both the B Pillars Cross section apart from these sectional forces are applied on the Short guns on both the sides and also on both the rail components of the model aswell. Which can be seen in the below figure.

After giving the sectional forces we join all the components.

This figure represents the assembly of all the components which were seperated to give the sectional forces.

Intrusions on the dash wall:

Here we create a new block with a name intrusion and select the nodes by entering their node id.

Locations for Measuring Vehicle Intrusions:

Review of the Model Intrusion:

The above figure represents the review of the intrusion alloted by giving the Particular node id's.

Results:

For Displacement :

Here from the above animation we can say that the maxim displacement is at a point 1.23E+03. Whereas the minimum displacement point 0

For Von Mises stress:

Bumper beams are impact absorber structures located in the front and rear of the vehicle and whose primary function is to protect critical parts of the vehicle and occupants. Bumper beams are applied to today's vehicles by being designed with different materials in various geometries with crash boxes.The main purpose of this dual system is to absorb the kinetic energy of vehicle and to ensure that occupants survive the accident with minimum damage.Since the cross-section of the bumper has effect on the crash performance, it can be designed in different cross-sections.The main physical phenomenon, where the structures used for energy absorption absorb energy, is plastic deformation. Keeping plastic deformation at maximum level is important in terms of the amount of energy that is absorbed. Therefore, the material used needs to be stiff but deformable. A non-deformable structure will act as rigid and transmit the force to the other parts without performing
its essential task which is energy absorption.

Cross-section materia,l wall thickness, loading conditions, which are the main parameters that significantly affect crashworthiness of bumper beam, are the most studied subjects by researchers.Certain parameters have been determined in the determination of crashworthiness of energy absorbing structures. The most important ones are the amount of absorbed energy, peak crushing force, mean crushing force, crash force efficiency and specific energy absorption.

The deformation conditions occurring on the wall and pole barriers of the bumper beam models designed for each geometry at the end of the crash analyses are shown in the above Figure While off-center deformation was observed on the pole barrier, deformations also occurred on the sides on the wall barrier. In addition, stresses were at maximum level on these areas because the end parts of all models were restricted to other degrees of freedom except the axis in which the speed was provided.

Here from the above animation the maximum von mise stress is of 3.745E-01 and the minimum is at initial point 0.

Acceleration Curve received on the accelerometer at base of B pillar :

• The acceleration Curve received on the accelerometer at base of B pillar is as in the above plottings.
• The maximum acceleration in 1st accelerometer is of 2.93606 mm/ms.
• The Maximum acceleration in 2nd accelerometer is of 8.8457 mm/ms.
• Therefore the accelerometer-2 has the maximum acceleration than the accelerometer-1.

Energy Curves:

Here from the above energy curves.

• As the Internal energy increases the kinematic energy decreases due to the conservation of the internal energy.
• When there is a collision with the rigid body the contact energy takes place from it's initial poin 20 ms to the final position 80 ms.
• Total energy is the addition of all the energies i.e TE= IE+KE+CE.

Local Variables:

For Pillars:

Here from the above pillar plottings.

• In this case forces are acting on the Z- Direction.
• The Maximum Force applied on the Pillar-A is 0.72 N at a point 42 ms.
• The Maximum Force applied on the Pillar-B is 0.88 N at a point 75 ms.
• Pillar-B has the maximum force compared to the Pillar-A.

For Short Gun:

Here from the above Short gun plottings.

• In this case forces are acting on the Z- Direction.
• The Maximum force applied on the Short gun-A is 1.31 N at a point 25 ms.
• The Maximum force applied on the Short gun-B is 6.03 N at a point 79.9 ms.
• Short gun-B has the maximum force compared to the short gun-A.

For Rail:

Here from the above Rail plottings.

• In this case forces are acting on the Z- Direction.
• The Maximum force applied on the Rail-A is 3.50 N at a point 10 ms.
• The Maximum force applied on the Rail-B is 5.75 N at a point 18 ms.
• Rail-B has the maximum force compared to the Rail-A.

For Bumper:

Here from the above Rail plotting.

• In this case forces are acting on the Z- Direction.
• The Maximum force applied on the Bumper is 16.47 N at a point 9 ms.

For Intrusion:

Here from the above Intrusions plotting.

• For the node-66244 has the maximum displacement of 931.816 mm
• For the node-66695 has the maximum displacement of 945.695 mm
• Node-66695 has the maximum displacement compared to the node-66244.

Conclusion:

Here from all the above cases we conclude that Frontal Crash Impact on the Finite element modelling practices used for crash analysis on the given BIW Model are studied and after effects of the different parameters on the vehicle have been reviewed. The aim of this work is to study the effects of such crash parameters on the dynamic response of automobile component through finite element approach path. These analyses mainly focus on software selected, crash type, vehicle/components considered for crashing, material used, type of element used, boundary conditions adopted tool used for post processing the results.