sbca96

03-27-2007, 04:31 PM

I just got the results back this weekend for the brake brackets I have

designed from the FEA engineer. The Finite Element Analysis (FEA)

was completed on the SolidWorks 2005 platform.

[u]Setup Data :</u>

[u]Using projected performance data :</u>

60mph to 0mph in 135ft.

[u]And equations based on projected performance data :</u>

vfinal=vinitial+a*t (vfinal=0)

d=dinitial+v*t+0.5*a*t^2 (dinitial=0)

Creates a calculated a=29ft/sec^2 deceleration which is about 0.9g’s

Round up to 1g for a safety buffer.

3500 lbs @ 1g braking = 3500 lbs braking force.

Front tires produce about 70% of the braking force:

3500 lbs * 0.70 = 2450 lbs

Force per front tire: Ftire = 2450 lbs / 2 = 1225 lbs

[u]Force applied to caliper:</u>

Fcaliper=Ftire*(Rtire/Rcaliper)=1225lbs*(13in/6in)=2650 lbs

This load will be applied evenly to the two caliper bolt holes.

[u]Results :</u>

The peak Stress Results show 12,000 PSI at the top mounting bolt

and is considerably lower than the yield strength of the material

(the 6061-T6 is 35,000-45,000 PSI depending where you look). This

is a 'worst case', in reality the stress would not be quite as

concentrated as is shown in the model, so you would only see peak

stresses around 10,000 PSI.

The Displacement Results show we get around three thousandths of

an inch of deflection at the front caliper bolt and around one

thousandth at the rear bolt. Since in reality the steel caliper

bridge ties these two together the caliper (and bracket) should

experience a deflection magnitude somewhere between these values.

http://hometown.aol.com/sbca96/images/avantibrakeproject/First_Article/FEA_bracket.jpg

[u]Clarification on GT bracket vs Cobra bracket :</u>

Six Grade 8 bolts are used in the middle (Stude used only 3) & Grade 10.9

bolts for the caliper (same as Ford). The GT bracket is what I tested, it

would be the "weaker" of the two. Technically that bracket wouldnt see

the level of stress that was found, unless it was used with a Cobra caliper.

The GT bracket only uses a 11 inch rotor, which would reduce the leverage

the caliper has. I figured lets see the worst case, and I will know it is that

much better off. If you notice the twisting on the bracket and the deflection

would both be less if the caliper bolt holes were better tied together. That

is not a problem since the Cobra bracket doesnt have that half moon cutout

in between the caliper mounting bolt holes. That will stiffen the bracket. If

the later 2 piston GT calipers are used for the GT size brakes, the "Cobra"

bracket can still be used, since the only reason the half moon is there is to

clear the early single piston GT caliper.

[u]Further reading:</u>

http://en.wikipedia.org/wiki/Finite_element_analysis

"The ability to model a structural system in 3D can provide a powerful and accurate analysis of almost any structure. 3D models in general, can be produced using a range of common computer aided design (CAD) packages. Models have the tendency to range largely in both complexity and in file format depending on 3D model creation software, and the complexity of the model’s geometry. FEA is a growing industry in product design, analysis and development in engineering. The trend of utilizing FEA as an engineering tool is growing rapidly."

Tom

'63 Avanti, zinc plated drilled & slotted 03 Mustang Cobra 13" front disc/98 GT rear brakes, 03 Cobra 17" wheels, GM alt, 97 Z28 leather seats, soon: 97 Z28 T-56 6-spd, Ported heads w/SST full flow valves, 'R3' 276 cam, Edelbrock AFB Carb, GM HEI distributor, 8.8mm plug wires

designed from the FEA engineer. The Finite Element Analysis (FEA)

was completed on the SolidWorks 2005 platform.

[u]Setup Data :</u>

[u]Using projected performance data :</u>

60mph to 0mph in 135ft.

[u]And equations based on projected performance data :</u>

vfinal=vinitial+a*t (vfinal=0)

d=dinitial+v*t+0.5*a*t^2 (dinitial=0)

Creates a calculated a=29ft/sec^2 deceleration which is about 0.9g’s

Round up to 1g for a safety buffer.

3500 lbs @ 1g braking = 3500 lbs braking force.

Front tires produce about 70% of the braking force:

3500 lbs * 0.70 = 2450 lbs

Force per front tire: Ftire = 2450 lbs / 2 = 1225 lbs

[u]Force applied to caliper:</u>

Fcaliper=Ftire*(Rtire/Rcaliper)=1225lbs*(13in/6in)=2650 lbs

This load will be applied evenly to the two caliper bolt holes.

[u]Results :</u>

The peak Stress Results show 12,000 PSI at the top mounting bolt

and is considerably lower than the yield strength of the material

(the 6061-T6 is 35,000-45,000 PSI depending where you look). This

is a 'worst case', in reality the stress would not be quite as

concentrated as is shown in the model, so you would only see peak

stresses around 10,000 PSI.

The Displacement Results show we get around three thousandths of

an inch of deflection at the front caliper bolt and around one

thousandth at the rear bolt. Since in reality the steel caliper

bridge ties these two together the caliper (and bracket) should

experience a deflection magnitude somewhere between these values.

http://hometown.aol.com/sbca96/images/avantibrakeproject/First_Article/FEA_bracket.jpg

[u]Clarification on GT bracket vs Cobra bracket :</u>

Six Grade 8 bolts are used in the middle (Stude used only 3) & Grade 10.9

bolts for the caliper (same as Ford). The GT bracket is what I tested, it

would be the "weaker" of the two. Technically that bracket wouldnt see

the level of stress that was found, unless it was used with a Cobra caliper.

The GT bracket only uses a 11 inch rotor, which would reduce the leverage

the caliper has. I figured lets see the worst case, and I will know it is that

much better off. If you notice the twisting on the bracket and the deflection

would both be less if the caliper bolt holes were better tied together. That

is not a problem since the Cobra bracket doesnt have that half moon cutout

in between the caliper mounting bolt holes. That will stiffen the bracket. If

the later 2 piston GT calipers are used for the GT size brakes, the "Cobra"

bracket can still be used, since the only reason the half moon is there is to

clear the early single piston GT caliper.

[u]Further reading:</u>

http://en.wikipedia.org/wiki/Finite_element_analysis

"The ability to model a structural system in 3D can provide a powerful and accurate analysis of almost any structure. 3D models in general, can be produced using a range of common computer aided design (CAD) packages. Models have the tendency to range largely in both complexity and in file format depending on 3D model creation software, and the complexity of the model’s geometry. FEA is a growing industry in product design, analysis and development in engineering. The trend of utilizing FEA as an engineering tool is growing rapidly."

Tom

'63 Avanti, zinc plated drilled & slotted 03 Mustang Cobra 13" front disc/98 GT rear brakes, 03 Cobra 17" wheels, GM alt, 97 Z28 leather seats, soon: 97 Z28 T-56 6-spd, Ported heads w/SST full flow valves, 'R3' 276 cam, Edelbrock AFB Carb, GM HEI distributor, 8.8mm plug wires