Mechanics of Deformable Bodies 85-218

Mechanics of Deformable Bodies 85-218

Objective:

To study the behaviour of ductile and brittle materials subject to torsion

Equipment:

1. Torsion testing machine Tinius Olsen 2. Micrometer 3. Scale

Specimens:

Standard torsion test specimens of steel, aluminum or cast iron

Procedure:

1. Using the micrometer measure the diameter of specimen to the nearest 0.02 mm at several points along the length of the specimen and record the average diameter. 2. Check the length of the torsion specimen (200.0 mm). 3. Mount specimen in the torsion testing machine. Set the load indicator dial zero. 4. Load and/or deformation increments will be as follows: Steel 56.5 Nm (500 in-lb) in the linear range 45q in nonlinear range Aluminum 33.9 Nm (300 in-lb) in the linear range 30q in the nonlinear range Cast Iron 28.25 Nm (250 in-lb) in the linear range 5q i 2 5. Apply the load slowly by manually operating the machine. Take readings of torque (T) and angle of twist (I) simultaneously, at the specified increments, without stopping the machine, and carefully record these experimental data. 6. When the yield point (for ductile material) is approached (as noted by the increased readings of angle of twist), the readings of the torque and angle of twist must be obtained more frequently so the stress-strain diagram will be well defined in this vicinity. 7. After the yield point (for ductile material) has been exceeded, apply the load until failure occurs. Readings in this range are based on deformation increments. 8. For cast iron, the specimen should be loaded manually until failure occurs. 9. Examine the fracture surface, and the type of failure that occurred in each specimen.

Report:

Prepare your Lab report according to the general instructions provided in the document on Structure & Format of Lab Reports. This is a formal report that should be written using a word processor; the only hand writing allowed is for the sample calculations. Include the following sections and results in the report: 1. Title page 2. Objectives 3. Procedures 4. Results a. Enter the experimental data into an Excel spreadsheet and calculate the shear stress and shear strain for each recorded data point. Plot a graph in Excel of the complete shear stress-shear strain curve for each specimen. Show on each graph the ultimate shear stress and the shear stress at the yield point. b. For each material, plot a graph showing the elastic portion of the shear stress – shear strain curve (including the yield point) to an enlarged scale. c. Sample calculations of the mechanical properties required in the data sheet and provide the completed data sheet (see the next page). d. Draw a 3D hand-sketch of the fracture surface of each specimen. Describe the fracture and comment on the reasons for this type of fracture. 5. Discussion 6. Conclusions 7. References (if needed)