3D Print Orientation: Impact on Strength of Suspension Arm?


#1

Hi Everyone,

I just watched Taylor’s latest video of his gearbox teardown and suspension arm replacement.

It appears there was a breakage that occurred (after many kilometers of successful travel!):
image

What i’m curious about is this: based on Taylor’s verbal description of the failure mode, it seemed like crack formation was present before there was impact with a rock, and the impact simply accelerated the crack propagation.

I’m not very familiar with 3D printing modes of manufacturing, but it occurs to me that from my Statics & Strength of Materials class (101) that in a simple model of an axially-loaded beam, the greatest stress occurs in the diagonal plane… which is very similar to what the video screenshot shows:

image

Untitled

It also occurs to me that 3D Printing as a manufacturing process, intrinsically produces very ANisotropic material (the Young’s Modulus, e.t.c can vary depending on orientation under consideration). I also came across this brief web-article that details someone’s test of this idea: http://www.sparxeng.com/blog/mechanical/3d-print-orientation-effect-part-strength

Perhaps future design iterations should have notes for the 3D printing orientation? Not sure if I’m over-thinking this :slight_smile:

Cheers,
Kai


#2

Taylor’s Video:

Rover Gearbox Update


#3

Good question Kai!

So I was probably unclear, but I only noticed the crack after several rock impacts. The final failure occurred when driving up a dirt ledge. So it was rock impacts, then it failed later, and in footage just before the failure I can see a crack was already there.

And the rock impacts occur when it drives up over some kind of larger rock and then the wheel drops off the big rock and the suspension arm impacts a smaller rock before the wheel hits the ground. Some of this also occurred when I was driving Rover through a concrete culvert repeatedly, which I will share footage of.

I’ve just uploaded a clip of Rover in that rock garden to show what it was like, though I don’t recall if any impacts occurred in that clip.

As far as print orientation - the parts definitely all have to be printed in a specific orientation, which I hope is mostly obvious. So far I don’t believe anyone has attempted to print any of these parts, but it would be worth documenting if I ever made documentation.