Additional teaching tools for this course can be found on the website for Mechanics of Materials by Beer, Johnston, and DeWolf.

Paper Stress Concentrations

Summary: This is a simple demonstration of the basic principles and behavior underlying stress concentrations. Stresses at points of load application can be much larger than the average stress in a member. The same is true when a member contains a discontinuity. Paper members with the same mid-span width are used to demonstrate the stress concentrations that can occur at load points as well as at discontinuities: holes and fillets.

Tower of Torque

Summary: Thrill your students with Tales of Torque using the versatile Tower of Torque! In its simplest form, the device allows students to predict and then measure the capacity of a simple bolt, modeled as a rod in torsion. The device has multiple uses detailed in other portions of this website.

The Big Book of Shear

Summary: Students often have difficulty with “what is shear?” and “stress/strain transformation is what?” To give a quick demonstration of pure shear and stress transformation, blocks are drawn on the side of a BIG book to show the effects of shear and transformation of axes.

Balloons

Summary: This is a simple demonstration of the basic principles underlying the behavior of thin-walled pressure vessels (TWPVs). A balloon or balloons are used to show that hoop stresses are twice as high as longitudinal stresses in cylindrical pressure vessels.

Hot Dogs

Summary: This is a simple demonstration of the basic principles underlying the behavior of thin-walled pressure vessels (TWPVs). A hot dog is used to show that hoop stresses are twice as high as longitudinal stresses in cylindrical pressure vessels and failure occurs along the length of the hot dog. The failure that occurs in the hot dog is due to hoop stress.

A Strainge Transformation

Summary: A thin rectangular sheet of rubber material is subject to an axial load. Stress blocks are painted or drawn on the rubber material. The stress blocks are oriented on a transverse plane (black square) and on a plane 45 degrees from the transverse plane (red square). Students have previously learned that only normal stress exists on the transverse plane and the 45 degree plane experiences the maximum shear stress. As the rubber material is stretched, the students can see that sides on the transverse stress block get longer in the longitudinal direction and shorter in the lateral direction, while the angles at the corners do not change. Students can use a ruler to compute the normal strain and Poisson’s ratio for the material. Similarly, on the 45 degree stress block, the lengths of all four sides increase the same amount and the angles change. The angles on the top and bottom corners get smaller and the angles on the left and right corners get larger. This demonstrates that shear stresses and strains exist within an object subjected to an axial load.

Design of Axial Members

Summary: This is a simple demonstration to introduce the basic principles of experimentation, analysis, and design in reference to axially loaded members. Copper wire is used to lift an object of known weight. In order to determine the minimum number of copper wire strands required to lift the load, students perform experiments, analysis and design calculations. The discussions in class inherently lead to an understanding of the practicality of experimentation, the need for a factor of safety in actual design, and actual-versus-allowable stress.

Paper Clip

Summary: We try to demonstrate failure of materials as a result of fatigue loading. We also are going to demonstrate the variability of fatigue strength within a population of paper clips.

Hands on Torque Strain in a Shaft

Summary: This simple, inexpensive, hands-on exercise allows students to see the deformation due to torque applied along the long axis of a circular shaft. The exercise is used as a lead in to a discussion of the nature of strain and the relationship between stress and strain in a torque loaded circular shaft.