simulation stress on wrench

WJT

Simple task - simulate the stresses between the head of a bolt and the box end of a mechanics wrench as torque is applied. What I am interested in is the stress at the box end of the wrench but I cannot figure out a way to mate/connect the wrench and bolt head such that the stresses from the actual points of contact are considered. Since Onshape does not translate tangent mates I am struggling to figure out how to set this up.

Here is what the study looks like when a fastened mate is created between the bolt (fixed) and wrench, and Mates is the selected Method. I expect to see stresses at the box end at the lines of contact with the corners of the bolt head. Clearly this is not realistic so how should I approach connecting these two parts?

GregBrown

Can you provide a link to this? I've done this exact example a few times… so can probably steer you in teh right direction.

WJT

Here it is, Greg.

https://diwmsi.onshape.com/documents/0f207296c7b6d1dbdb5dcb92/w/f408181d8b2a9adcdcdd5a70/e/7f09af5c6405f641fe77245b?renderMode=0&uiState=684c8c44413a5c6f42a70d8a

eric_pesty

I'm guessing you'll need to split the contact areas and use the "simulation connection" options in the mate dialogue to specify which faces are "fastened"

chris_gromek_onshape

Greetings WJT,

Thank you for providing a copy of your simulation wrench model. As Eric correctly suspects, we have split the faces and used Simulation Connections to selectively apply Mates between the two Parts.

In this particular case, we have applied a series of three Planar Mates, each of which enforces a sliding planar interface between the compressive halves of the wrench's parallel faces. In order to achieve this effect, one must:

1. Split the faces of the wrench in (approximately) half. I happened to make the loaded portion slightly smaller than the unloaded portion, since I know that there is a slight "spill over" in the Simulation Connection region.
2. Create a set of Mate Connectors associated with the wrench that coincide with the bolt's faces (or visa versa). Since the bolt and the wrench are modeled with slight clearances, these additional Mates are necessary. The clearances here are small enough that the simulation elements will easily span the gap.

As one might expect, the differences in results between a Fastened interface and this Thrice-Planar interface are two fold:

1. The "Fastened" model artificially lowers the stresses on the regions of the wrench in contact with the bolt.
2. The "Fastened" model places more strain on the arm of the wrench than does the "Planar" model, which has more "give" to it.

The choice of loading strategy is somewhat up to you. I have chosen to apply a moment over the faces of the wrench handle, but a linear force would do just fine.

I hope that helps and thank you for the question! Please write back if we can help clear up anything else.

Best Regards,
Chris