KEYWORDS:- Engineering mechanics, Forensic Engineering.

INTERODUCTION:- FORENSIC ENGINEERING :-Forensic engineering is

defined as“ the application of the engineering science to investigation of failure or other performance problems .” generally the purpose of Forensic engineering investigation to locate causes of failure with a view to improve performance or life of a component or to assist a court in determining the facts of an accidents.

ENGINEERING MECHANICS:- “it is that branch of science which treats of the effect of force upon matter”

Forensic engineering case studies are well suited to inclusion in

the classroom for the following reasons:- The direct application of concepts from engineering science to a

real physical application. They allow the student to apply the scientific method, formulating

a likely accident scenario (hypotheses).

APPLICATION:- Most manufacturing models will have a forensic components that monitors early failure to improve quality or efficiency. Most engineering disasters are subject to forensic investigation by engineers experienced in forensic methods of investigation. Rail crashes, aviation accidents and some automobile accidents are investigated by forensic engineers, where component failure is suspected.

CASE STUDY:- A series of forensic engineering case studies

has been formulated these case study are presented in the next two sections. They have been developed for used in an introductory course sequence in engineering mechanics, including

the first courses in static and dynamics of materials.

ANALYSIS OF A LADDER ACCIDENT –FORENSIC ENGINEERING APPLICATION OF ENGINEERING

STATICS :- DESCRIPTION OF THE ACCIDENT :- A person

5’11” tall and of weight 210lb was injured in a fall from a ladder. A witness at the scene indicates that the man had climbed about two-thirds of the way of the ladder, when both he and the ladder fell in the ground. The climber sustain a broken left arm and has no memory of the details of the accidents.

DESCRIPTION OF THE ACCIDENT SCENE -

THE SITE -

TASKS AT HAND:- Develop a simple mathematical model of the system, using

principles of static. Formulate a hypothesis as to how the accident occurred. Using the mathematical model, to prove or disprove your

hypothesis. Draw conclusion.

THE SOLUTION:-

THE MODEL:-

By using the principle of static

Equilibrium, the following Equation apply -

Rx = Ru sinө N - W + Ru cosө = 0

Wx cosө = Ru L

THE LIKELY ACCIDENT SCENARIO HYPOTHESIS:-

we have found that the accident occur due to these values- L=9ft X=6ft θ=60° by solving the above equations, Rx= 70lb. Ru = 60.6lb. N = 175lb. The coefficient of the friction for metal on stone should be in the

range of 0.30 to 0.70, but here it is less then 0.30 and a check of the ladder setup indicates that θ=60° angle of setup is less than 75° setup angle recommended for the ladder.

solve the equation with the following setup parameter- L = 8.1ft x= 8.1ft θ=75° the results are as follows Rx= 54.41lb. Ru = 52.51lb. N = 196lb.

.

the ladder would not have slipped out if the recommended setup angle had been used. Therefore, it is likely that an improper setup of the ladder resulted in the conditions that caused the accident

ANALYSIS OF A TRAFFIC ACCIDENT- FORENSIC ENGINEERING APPLICATION OF ENGINEERING DYNAMICS:-

DESCRIPTION OF THE ACCIDENT:-A small two-door

economy car and a large four-door sedan were involved in a traffic accident. The economy car was traveling east through a intersection on a road with a stop sign in the intersection. The sedan was traveling north through the same intersection on a road with no traffic control device. The cars collided in the intersection and came to rest in a parking lot on the north east corner of the intersection.

DESCRIPTION OF THE ACCIDENT SCENE-

THE VEHICLES-

TASK AT HAND:-Develop a simple mathematical model of the system, using principles of dynamics.Formulate the hypothesis as to how the accident occurred.Using the mathematical model, to prove or disprove your hypothesis.

Draw conclusion.

THE SOLUTION:-

THE MODEL:- The collision will be modeled using principles of work and energy.

The two vehicles lock together upon impact and that there total kinetic energy at the instant of impact is dissipated by sliding friction :

(W1+W2)v2/2g=(W1+W2)µd

the velocity vector of the two-car system immediately following the collision can be obtained as follow :

v=v cosθi +vsinθj the principle of conservation of momentum can be applied to

determine the individual speed of each vehicle immediately prior to the collision:

w1/g v1i+w2/gv2j=(w1+w2)/gv

the velocity or acceleration relationship under the assumption of constant acceleration :

voi= (vi2+2µgD)1/2

where voi is the speed of vehicle immediately prior the breaking.

LIKELYTHE ACCIDENT SCENARIO HYPOTHESIS :-

TEST OF HYPOTHESIS :- The information about vehicles, and

library research yields the following values for use in equation w1=2500lb w2=3500lb µ=0.71 ( for rubber on asphalt) g=32.2 ft/s d=94 ft based on these values the collision is found to be v=65.6 ft/s. the velocity vector associated with the two cars immediately

following the collision is found to be v=(22.4 ft/s)i+(61.6 ft/s) j there are two possible driver action to be considered for the economy

car *the driver could have stopped at the stop sign accelerated in to the

intersection and been hit by northbound sedan. *the driver could have failed to stop at the stop sign, and proceed into

the intersection without stopping. Using a form of the velocity /acceleration relationship: v2=vo2+2a(x-x0)

the maximum propulsive force that can be generated by the friction at the interface is over 30 foot interval:

using F=ma, µw1=1775 pounds. in conclusion the sedan was traveling at speed of approximately

75mph when braking began. This is well in excess of the posted 35mph speed limit for the intersection.

CONCLUSION :- The use of forensic engineering case studies introductory mechanics courses has been proven to be an effective means to motivate student interest and bring ‘real world ’ application in the classroom. These case studies require extensive analytical skills and quantitative reasoning abilities, but do not require the extensive use of design processes and tools required for design base case studies.