This assignment was done in collaboration with Youngjin Yang.

Overview

This project required us to design a torque wrench by choosing a material and dimensions to satisfy safety and gauge output requirements. Simulation was done in Ansys to verify our theoretical calculations.

FEM Analysis Results

Dimensions

The torque wrench center was 16 in from the end. It had a width of 1.3 in and a thickness of 0.1 in. Drawings and CAD are below.

Material Properties

We used Ti-6Al-4V titanium alloy for the wrench. The key material properties are:

• Young's Modulus: 16.5 × 10⁶ psi
• Poisson's Ratio: 0.34
• Tensile Strength: 135,000 psi
• Fracture Toughness: 80,000 psi√in
• Fatigue Strength: 74,000 psi

Torque Wrench Sensitivity

The strain gauge has a gauge factor of 2, and we are assuming a half bridge design. Based on the FEM strain, the wrench sensitivity is 1.214 mV/V. This passes the design requirement of an output > 1.0 mV/V

Strain Gauge Selection

We chose the Micro Measurements 015LW strain gauge, which is a linear (uniaxial) gauge with a 0.075-inch active length and a gauge factor of 2.0. It fits easily in our design since it needs less than 0.1 inches of space. The small size works well for our application, though a larger gauge would have been easier to install if we had more room.