Detemination of Steel Alloy

 

The material was selected using a material properties table from Machine Elements of Mechanical Design (Mott, 5th ed). This list was used to select the alloys of steel with the highest combination of hardenability and ultimate strength. From the given data the optimum alloys were determined to be SAE 5160 OQT 400 and 4140 OQT 400. Due to availability and prices, the 4140 alloy was selected as the original material.

 

 

Detemination of Link Size

 

The size of the links was determined by calculating the force that can be applied with a set of bolt cutters and then creating a formula for the mininum cross sectional area which could withstand that applied force. The ultimate shear strength of SAE 5160 Steel OQT 400 (241.5 ksi) were used as the maximum allowable stress for these calculations. Once the minimum acceptable area was determined a standard cross-section of flat bar steel was found. The final dimensions of chain link stock was decided to be 1.25 x 0.33 inches. 

 

 

Selection of Rivet Size

 

Stainless steel was selected to be the rivet material, due to the availability and strength. Next the ultimate tensile strength of 301 Stainless Steel (74.7 ksi) was used to create a formula for the minimum allowable diameter in order to avoid tensile failure. The amount of force that can be applied with a prybar was calculated, along with the force that could be applied by using the links themselves as a lever. Stress calculations were used to determine the maximum stress applied to the rivet, and the minimum acceptable diameter to resist that stress.The stress in the rivet head was determined to be too large for the  standard rivets to be used. Because of this the design of the rivet housing was altered to include a steel washer between the links, which prevents the nose of a prybar from fitting between the links. Although the stress in the head is not an issue anymore, the minimum acceptable rivet diameter was selected to be 1/8th of an inch. In order to maximize security, the largest rivet size which fits in the housing can be selected. The rivet size selected was 5/16ths of an inch. 

 

 

Final analysis of dimensional requirements. 

 

A calculation of the overall weight and and volume was completed. This analysis showed that the folded volume of the chain was adaquate, however the overall length of the chain (74.75 inches) was exccessive and the weight of the assembly, 12.5 lbs) was over the maximum allowable amount (10 lbs). In order to optimize these measurements the previous analyses were recalculted using the properties of SAE 5160 OQT 400. Switching materials does increase the price of the raw materials, however it also allows for a decrease in the thickness of each link which reduces the weight to an acceptable value. 

 

Final Dimensions:

 

Link material: SAE 5160 OQT 400

Cross-section of links: 1.25 x 0.25 inches

Overall length of each link: 15 inches

Rivet material: Stainless Steel 301

Rivet head type: Flat Head

Rivet shank diameter: 5/16th inches

Rivet shank length: 0.750 inches