SMC 4133 AUTOMOTIVE STRUCTURES DESIGN FOR BODY TORSION

SMC 4133 AUTOMOTIVE STRUCTURES DESIGN FOR BODY TORSION Body torsion strength requirement • The body has to recover its shape with little to no permanent deformation during twist ditch maneuver • The twist ditch torque can be obtained by multiplying axle load (W) by half of the wheel track (t). • The angle of twist can be determined by 2 x deflection divided by width of the loaded points (w) All materials in this slide are taken from Donald E Malen. 2011. Fundamentals of Automobile Body Structure Design , SAE International.

SMC 4133 AUTOMOTIVE STRUCTURES DESIGN FOR BODY TORSION Torsion stiffness requirement: 1. To ensure good handling properties 2. To ensure a solid structural feel and minimize relative deformations – squeaks & rattles - As a vehicle turns a corner, it will roll and causes a weight transfer. It then can affect steering characteristics - High body torsional stiffness is required to ensure good vehicle handling - Typical roll stiffness is 1000 Nm/deg while ride spring rate = 23. 4 N/mm All materials in this slide are taken from Donald E Malen. 2011. Fundamentals of Automobile Body Structure Design , SAE International.

SMC 4133 AUTOMOTIVE STRUCTURES DESIGN FOR BODY TORSION - Let’s view the stiffness system as a series connection of springs - Keff/Kroll = 1. 0 - Kbody = 10 Kroll - Kbody = 10000 Nm/deg for good handling For good solid structure feel: - Vehicle torsional frequency from 22 -25 Hz - Torsional stiffness = 12000 Nm/deg - Torsion strength = 6250 Nm All materials in this slide are taken from Donald E Malen. 2011. Fundamentals of Automobile Body Structure Design , SAE International.

SMC 4133 AUTOMOTIVE STRUCTURES DESIGN FOR BODY TORSION Load Path Analysis - To determine loads on individual structure elements - With these loads those elements can be designed Let’s begin with a simple structure i. e. a closed box. The box is loaded by a twisting couple at the front and rear corners All panels are loaded All materials in this slide are taken from Donald E Malen. 2011. Fundamentals of Automobile Body Structure Design , SAE International.

SMC 4133 AUTOMOTIVE STRUCTURES DESIGN FOR BODY TORSION - Edge loads & shear flows can be calculated - AQ = T A is a coefficient matrix Q is an edge load matrix T is an applied torque matrix Shear flow, q = Q/L (N/m) All materials in this slide are taken from Donald E Malen. 2011. Fundamentals of Automobile Body Structure Design , SAE International.

SMC 4133 AUTOMOTIVE STRUCTURES DESIGN FOR BODY TORSION Example 1 Determine the edge loads for the torsion case All materials in this slide are taken from Donald E Malen. 2011. Fundamentals of Automobile Body Structure Design , SAE International.

SMC 4133 AUTOMOTIVE STRUCTURES DESIGN FOR BODY TORSION Example 2 All materials in this slide are taken from Donald E Malen. 2011. Fundamentals of Automobile Body Structure Design , SAE International.

SMC 4133 AUTOMOTIVE STRUCTURES DESIGN FOR BODY TORSION Example 2 Determine the edge loads for the given torsion load case All materials in this slide are taken from Donald E Malen. 2011. Fundamentals of Automobile Body Structure Design , SAE International.

SMC 4133 AUTOMOTIVE STRUCTURES DESIGN FOR BODY TORSION Analysis of body torsional stiffness: Closed box - Energy method will be used to predict torsional stiffness by taking into account panel dimensions, thicknesses and material properties All materials in this slide are taken from Donald E Malen. 2011. Fundamentals of Automobile Body Structure Design , SAE International.

SMC 4133 AUTOMOTIVE STRUCTURES DESIGN FOR BODY TORSION Effective shear rigidity - to predict realistic torsional stiffness where in reality the body panels differ considerably from an ideal flat plate - Typically, the body panels are crown shape, have holes, cut-outs and framework with flexible joints All materials in this slide are taken from Donald E Malen. 2011. Fundamentals of Automobile Body Structure Design , SAE International.

SMC 4133 AUTOMOTIVE STRUCTURES DESIGN FOR BODY TORSION Example 3 Determine torsional stiffness of a box van based on: a) Given shear rigidity b) Effective shear rigidity: rear hatch opening Data: w = 1400 mm, h = 1250 mm, L = 2000 mm, G = 80000 N/mm^2, t = 1 mm Solution: a) K = (2 x 1400 x 1250)^2 x (1/(2 x(21. 9+35+31. 3)) = 6. 95 E+10 Nmm/rad = 1. 22 E+6 Nm/degree b) Work done = Energy in the joints ½ x F x delta = 4 x ½ x Kj x theta^2 theta = delta/b, S = 4 Kj/b^2, Gt = 4 Kj /ab Given Kj = 0. 1 E+8 Nmm/rad a) K = (2 x 1400 x 1250)^2 x (1/(21. 9+35+35+31. 3+76553)) = 1. 6 E+8 Nmm/rad = 2807 Nm/degree All materials in this slide are taken from Donald E Malen. 2011. Fundamentals of Automobile Body Structure Design , SAE International.

SMC 4133 AUTOMOTIVE STRUCTURES DESIGN FOR BODY TORSION Analysis of body torsional stiffness: Sedan Gt = (Q/delta) x (H/L) Delta is obtained from FEA All materials in this slide are taken from Donald E Malen. 2011. Fundamentals of Automobile Body Structure Design , SAE International.

SMC 4133 AUTOMOTIVE STRUCTURES DESIGN FOR BODY TORSION Example 4 From Example 2, determine the cabin torsional stiffness with side-frame. q = 2678/1250 = 2. 1414 N/mm q/T = 2. 77 E-7 mm^-2 Let Q/delta = 374. 5 N/mm, Gt 7 -8 = 374. 5 x 1250/2000 =234 N/mm (side frame) A 1=A 5=1170000 mm^2, A 2=1103087 mm^2, A 3=1950000 mm^2, A 4=872067 mm^2 A 6=3120000 mm^2, A 7=A 8=2312500 mm^2 Gt 1 -6 = 80000 N/mm Thus, K = 6. 55 E+ 8 Nmm/rad = 11491 Nm/degree All materials in this slide are taken from Donald E Malen. 2011. Fundamentals of Automobile Body Structure Design , SAE International.