Aluminum or Nylon & Mechanics of a spacer.

  • Thread starter Thread starter an1mal_69
  • Start date Start date
  • Tags Tags
    Aluminum Mechanics
Click For Summary
SUMMARY

The discussion centers on the use of Acetal Nylon versus Aluminum for a spacer in a front suspension system, specifically regarding its compressional and shear stress properties. The proposal involves inserting a 30mm spacer between the wishbone arm and the ball joint, secured with four bolts. Concerns were raised about the shear stress on the nylon spacer, with the consensus that the fasteners should primarily handle tension due to preload. It was concluded that the low coefficient of friction between nylon and aluminum necessitates increased preload on the bolts to prevent joint failure due to shear sliding.

PREREQUISITES
  • Understanding of mechanical engineering principles, specifically in suspension systems.
  • Knowledge of material properties, particularly compressional and shear stress characteristics of Acetal Nylon and Aluminum.
  • Familiarity with fastener preload and its role in joint integrity.
  • Basic understanding of friction coefficients and their impact on mechanical joints.
NEXT STEPS
  • Research the mechanical properties of Acetal Nylon compared to Aluminum in load-bearing applications.
  • Learn about calculating preload requirements for fasteners in mechanical joints.
  • Investigate methods to increase the coefficient of friction in joints involving different materials.
  • Explore failure modes in mechanical joints, focusing on shear sliding and joint integrity.
USEFUL FOR

Mechanical engineers, automotive suspension designers, and materials scientists interested in optimizing joint performance in suspension systems.

an1mal_69
Messages
4
Reaction score
0
Moderator's note: thread moved from Homework Help forums to Mechanical Engineering forum. Welcome to PF an1mal_69 :smile:

Apologies, this is not homework, but a real world problem.

Homework Statement


Front suspension system, consisting of 2 wishbones supporting a wheel hub via (x2) ball joints at the top and bottom. Other connections are apparent, for steering etc, but not relevant in this instance. The ball joints are secured to the arms with 4 bolts.

The proposal is to template the top ball joint and insert a spacer of around 30mm between the arm and ball joint using extended and uprated fasteners.

I had intended to make the spacer from Acetal Nylon having compressional properties equal to or greater than Aluminum. Certain individuals have questioned the material citing the spacer will be subject to shear stress, I argued the fasteners would be taking the shear loads.?


balljointmock.jpg



If you take the rough diagram into consideration..assume the bottom plate as fixed, and there are (x4) fasteners clamping the spacer in place. If a force is applied to the bar on the upper plate (in any direction) what are the effects/loads on the spacer.?

Many thanks in advance, Nik..
 
Last edited by a moderator:
Physics news on Phys.org
Ideally, shear forces should be absorbed by friction in the joint and the fasteners should only see tension due to their initial preload. If the joint slides (thus applying shear to the fasteners) it could be considered a joint failure.

Unfortunately, the coefficient of friction between nylon and aluminum is probably pretty low, especially when compared to bare aluminum on aluminum (which is around 1.0-1.1 I think). This means if you use a nylon spacer, you will need to apply more preload on the bolts to prevent a joint failure (shear sliding).