Starting thread ahead of the presentation for a change.
Rob Schwartz and I will be building some test panels for destructive testing at the upcoming meeting. I will be posting my math here as I figure out how much they should take before failure.
I have done a previous presentation on the topic of composite battery boxes, when we were prepping for the Porsche modification. That presentation was light on math, and heavy on costs and concepts. http://www.fveaa.org/forums/index.php/topic,1286.0.html
This time around it will be more math and destruction. Can't have destruction without the math.
As usual around here we will be using the Kevlar left over from the Porsche and Dakota. KEVLAR® 5oz from US Compositeshttp://www.uscomposites.com/kevlar.html
Their spec sheet is seriously light so we have to go back to the manufacturer of the yarn it is made out of. http://www.matweb.com/search/datasheet.aspx?matguid=77b5205f0dcc43bb8cbe6fee7d36cbb5&ckck=1
Physical Properties Metric English Comments
Density 1.44 g/cc 0.0520 lb/in³
Water Absorption 3.5 % 3.5 % As shipped; Typical moisture levels on yarn as shipped; they reflect values reached at normal, moderate temperature and humidity levels following fiber production, which is a wet process.
Moisture Absorption at Equilibrium 3.5 % 3.5 % Equilibrium from Bone-Dry Yarn; Equilibrium values are determined by bone drying the fiber and condition at 75°F (24°C), 55% RH.
Mechanical Properties Metric English Comments
Tensile Strength, Ultimate 3000 MPa 435000 psi Breaking Tenacity 3620 MPa 525000 psi Epoxy-impregnated strands, ASTM D2343
Elongation at Break 2.4 % 2.4 %
Tensile Modulus 112 GPa 16300 ksi
Tenacity 2.08 N/tex 23.6 g/denier
Poissons Ratio 0.36 0.36
Thermal Properties Metric English Comments
Specific Heat Capacity 1.42 J/g-°C
@Temperature 25.0 °C 0.339 BTU/lb-°F
@Temperature 77.0 °F
Thermal Conductivity 0.0400 W/m-K 0.278 BTU-in/hr-ft²-°F
Maximum Service Temperature, Air 149 - 177 °C 300 - 351 °F For long-term use
Shrinkage <= 0.10 % <= 0.10 % In water at 212°F (100°C) and in air at 351°F (177°C)
Red highlighted is one of the key items here.
Since this is the yarn, we will need to adjust for the fact that half the yarn is running in the wrong direction for our test. So our tensile strength will be 262,500psi in a single direction for the fabric in question in our planned test. Steel is in the 80,000 range. Fabric total thickness is 0.0095 inches, so if we end up building something that is one foot wide, the tensile strength of one side will be 0.0095*12= 0.114 square inches multiplied by the ultimate tensile strength of the fibers that are running in the direction of interest gives us a ultimate tensile strength of 29,925 pounds per side. Various people report that Kevlar is equally good in compression and tension so for our purposes I will assume it is equal.