Chassis Impact Analysis

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International Journal on Theoretical and Applied Research in Mechanical Engineering (IJTARME)

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ISSN (Print): 2319-3182, Volume -6, Issue-1-2, 2017 112

Chassis Impact Analysis

Snehal G Sakhare

Department of Mechanical Engineering, Indira College of Engineering and Management, Pune Savitribai Phule Pune University, India

Email: [email protected] Abstract- .In real life we have only partial information’s

about the circumstances of the vehicle crash and vehicle itself. This fact inspires researching on modeling techniques which not require the detail knowledge of physical and mechanical parameters of the examined vehicle, but deal with just a few data, which are relatively easy to measure (quantities which are measurable without looking inside the vehicle, for example velocity, deformation, acceleration, time etc.

A front collision in which a vehicle runs front to front is considered. This case can be analyzed assuming that the crush is ‘plastic’. In the development of a new vehicle platform, its crashworthiness is an important concern, and it is imperative to compare the impact severity of the vehicle and occupants under various test and Design conditions. Since an impact is a physical event that involves analyses of impulses and energy Components, such as kinetic energy, energy absorption, and energy dissipation, the analyses require Both the principle of work and energy and that of impulse and momentum Any crash event involves not only impact and excitation, but also energy absorption and loss. In collisions among multiple vehicles the crush energy absorbed by each vehicle determines the crash

Severity for that vehicle. In this paper we find the full and one third collision of vehicle in two cases and find how much energy absorbed on both vehicles and its parts attached with chassis.

I. INTRODUCTION

Modeling of the deformational force and absorbed energy plays a very important role in different fields of vehicle engineering. The usually applied FEM based methods give good approximations, but they have extremely large computational complexity. On the other hand there exist simple force models, but they not approximate well in details the real data. The aim of this project is to introduce a force model for vehicle deformation, which is able to describe the real process and have acceptable.

In the development of a new vehicle platform, its crashworthiness is an important concern and it is imperative to compare the impact severity of the vehicle and occupants under various test and design conditions.

Since an impact is a physical event that involves analyses of impulses and energy components, such as kinetic energy, energy absorption, and energy dissipation, the analyses require both the principle of work and energy and that of impulse and momentum.

Although both principles are derived from Newton’s Second Law, they are not mutually exclusive when it

comes to solving problems involving impact and excitation. In this project we work on the impact analysis of sumo’s chassis where different speed assume whose force is same applied on front and 1/3^rd collision of chassis because now a day’s maximum 1/3^rd collisions of vehicles are done. In this we find the energy absorbs on both vehicles and there different parts attached in chassis.

ABSOLUTE MOMENTUM NOTION - This approach uses a comparison of the momentum of the bullet vehicle in each example considering its absolute speed at impact in one collision relative to that in the other. As in the absolute energy motion, the underlying reasoning is that this approach considers the total momentum the bullet vehicle “brings” to the collision event, and, since it is the

“Striking” vehicle, its potential for damage (and injury) is represented by its momentum.

II. MATERIAL AND PROPERTIES

Material: Steel, the material typically used in vehicle structures, allowed for the economicmass production of millions of units over the past seven decades.

Basicrequirements for body structure materials include good formability, corrosionresistance, and recyclability.

Body materials should also posses’ sufficient strengthand controlled deformations under load to absorb crash energy, yet maintainsufficient survivable space for adequate occupant protection should a crashoccur. Further, the structure should be lightweight to reduce fuel consumption.The majority of mass- produced vehicle bodies over the last six decades weremanufactured from stamped steel components.

Manufacturers build only a fewlimited production and specialty vehicle bodies from composite materials oraluminum. Although a patent for an all-steel body was granted in 1900, until the 1920’s, automakers built vehicle bodies from a composite of wood panels joined with steel brackets. Steel sheets were added over the panels to provide a better surface to hold the paint. As metallurgists improved the formability of sheet steel and toolmakers built durable dies capable of stamping millions of parts and spot weld technology allowed for joining large body shells, the all-steel vehicle

Properties

Density 7.86*10⁻⁶kg

Poisson’s ratio 0.3 Modulus of Elasticity 205 GPa

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Yield Tensile Strength 250MPa

III. ANALYTICAL CALCULATIONS

Let small vehicle as – bullet vehicle

Assume mass & initial speed = 2500 kg & 80 km/hr Let heavy vehicle as – target vehicle

Assume mass & initial speed= 17000kg & 35 km/hr Calculations:

Consider light vehicle sumo as a Bullet vehicle

& heavy vehicle truck as a target vehicle Let sumo be the bullet vehicle

(1) Assume initial velocity (V1) = 80 km/hr.

&Mass (M1) = 2500 kg.

(2) Let truck be the target vehicle

Assume initial velocity (V2) =35 km/hr.

& Mass (M2) =17000 kg.

(3) Final velocity of vehicle 1 & 2 are:

V1¹ = V1 * M1/(M1+M2) V2¹ = V2 * M2/(M1+M2) (4) Closing velocity V close = |V2-V1|

(5) Separation velocity V sep = |V2’- V1'|

(6) Coefficient of restitution e= | V sep/V close |

(7) Loss of kinetic energy:

∆E = ½(M1M2)[1-e²/(M1+M2)](V1-V2)² (8) K.E Distribution:

(a) In front bumper = ½ mv² (b) In side rod = ½ mv² (9) Change in velocity:

(a) Bullet vehicle ∆V = V1'-V1

(b) Target vehicle:

∆V = V2'-V2

(10) % of energy loss:

∆E = (1-e²)%

(11) K.E before impact

K.E pre impact = 1/2(M1V1²)+1/2(M2V2²) (12) K.E after impact

K.E post impact = 1/2(M1V1'²) +1/2(M2V2'²)

(13) Comparing pre impact & post impact total energy:

∆E = K.E pre impact – K.E post impact (14) Momentum:

Total momentum pre impact= M1V1+M2V2 Total momentum post impact=

M1V1’+M2V2’

(15) Total system change of momentum:

∆P= P-P’

(16) Strain = 1-K.E final/K.E initial

(17) Impact force F = W [1+√(1+(2Ch/W))]

Where W= load, C = constant =AE/L

(18) Mass R (μ) = M2/M1

(19) Total energy absorbed by both vehicles during crush

E def = ½[(M1.μ) / (1+μ)] Vc (20) Energy absorbed by each vehicle E1 = M1 E def/ (M1+M2) - For light vehicle E2 = M2 E def/ (M1+M2) - For heavy vehicle (21) Energy absorbed by other components 1) Radiator: E def = ½[(M.μ) / ( 1+μ)] Vc Er = M*E def / (M1+M2)

2) Engine: E def = ½[(M*μ) / (1+μ)] Vc Ee = M*E def/(M1+M2)

CRASH TEST#1 CRASH TEST#2

BULLET TARGET BULLET TARGET

VEHICLE MASS 2500kg 17000kg 2500kg 2500kg

VEHICLE INTIAL ABSOLUTE VELOCITY 80 km/hr 35 km/hr 80 km/hr 60 km/hr

VEHICLE FINAL ABSOLUTE VELOCITY 2.84m/s 8.47 m/s 11.11 m/s 8.335 m/s

CLOSING VELOCITY 12.5 m/s 5.55 m/s

SEPERATION VELOCITY 5.63 m/s 2.775 m/s

COEFFICIENT OF RESTITUTION 0.4504 0.5

BULLET VEHICLE ∆V 19.38 m/s 11.11 m/s

TARGET VEHICLE ∆V 1.25 m/s 8.335 m/s

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INITIAL (AT IMPACT) ENERGY 1.420*10⁶ J 964.52*10³ J

FINAL (POST IMPACT)ENERGY 619.879*10⁶ J 241.13*10³ J

ENERGY “LOST ”(COMPARING TOTAL ENERGY PRE IMPACT WITH THAT POST IMPACT)

800.12*10³ J 723.39*1O³ J

ENERGY “LOST” (BASED ON VELOCITIES) 135.73*10³ J 14.43*10³

TOTAL SYSTEM ENERGY POST IMPACT(P) 220.29*10³ Kg m/s 97.225*10³ Kg m/s TOTAL SYSTEM ENERGY POST IMPACT(P’) 151.09*10³ Kg m/s 48.61*10³ Kg m/s

TOTAL SYSTEM CHANGE OF MOMENTUM 69.7*10³ kg m/s 48.61*10³ Kg m/s

IV. CONCLUSION

The chassis gives the stresses and energy distribution on both the vehicles with full and 1/3^rd collisions. By the formulation we also find the energy distributed on each parts of the chassis.

So, from the above analytical as well as Ansys software analysis it has been found that the maximum stresses are generating on the chassis due to the impact with other vehicles. These stresses cannot be avoided but can be properly regulated with the addition of body guard in front bumper.

Sr.

No.

Analysis Analytical Result

Ansys Result 1 Total

Deformation

0.46375 mm 2 Equivalent Stress 250 MPa 223.18 MPa 3 Equivalent strain 0.56 0.0011159

mm

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