The Stress of Strain
Stephanie Poyer
Stonewall Jackson Middle School, Hanover County
Developed with funding from the American Council of Engineering
Companies of Virginia and the Math Science Innovation Center.
Question
Stress and Strain. What materials make buildings the strongest?
Standards of
Learning
Physical Science, Pre-Algebra.
Virginia Standards of Learning: Science (2010) PS.1, PS.6; Math (2009)
8.12, 8.13
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21st Century
Curriculum
Engineering: Nature of STEM 1.23; Design and Build 2.22; Civil
Engineering 4.43.
Background
Students will understand the process of how engineers conduct materials
testing to determine the ultimate tensile strength of a beam. Students must
know and understand how to solve ratios. Prior to this activity the
concepts of stress, strain, and deformation will be introduced. Review the
process of making ratios.
Safety
The cured clay will be hot when it comes out of the oven. Do not bake the
clay in a microwave, and follow all baking instruction on the package of
the clay.
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Materials
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Procedure
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Engineering Activity
Supplies are for EACH pair of students participating in this
activity
2 oz of polymer clay, such as “sculpey clay”- packaged in 1.74
lbs. (For more information-visit http://sculpey.com/teacherslounge.htm
String or rope about 2 feet
Weights to hang on strings (or textbooks can be used)
Scale to measure beam weight.
Divide the 1.75 lbs of clay into 2-oz. cubes, resulting in 14 equal
cubes
For the stress testing, make sure you have a place, such as between
two tables, desks or chairs, to rest the beams and add the weights.
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Engineering Activity
If you want to cure the clay with students, preheat the oven to
275◦ F.
Make two long, thin lengths of clay for demonstration. Cure one
piece in the oven, but not the other piece.
Ask students to vote on the following question, “Do engineers
construct buildings with solid beams or hallow beams?” Tally the
responses on the board. Tell them they will find out more about
what engineers do in this activity.
Use an uncured length of clay to demonstrate plastic deformation
by putting across a gap and showing that it bends, but does not
spring back to its original shape, after a weight is added to it and
removed. Use the cured length of clay to demonstrate elastic
deformation by showing that the clay returns to its original shape
after the weight is removed. Challenge the students to design a
beam that is very strong, but does not weigh very much.
Divide the class into groups of 2-4 students in each group.
Give each group a 2-oz cube of clay. Explain that using less clay
may increase their strength: beam weight ratio.
Have students design a 7-inch long beam to span a 6-inch gap.
Ask students to sketch their ideas for various designs before
constructing the one they predict will have the best strength: beam
to weight ratio. The beams can be square, circular, l-shaped,
triangular or any other shape they think will be successful.
During beam construction, suggest students use a pencil point to
help join vertical clay slabs to any horizontal clay slabs
(perpendicular surfaces) of a beam design. This reduces any gaps
between two surfaces, which would weaken the beam.
Follow the directions on the packaging to cure the clay beams by
baking them in the oven. This can be done at the end of the day or
overnight.
To complete the curing process, let the beams cool to room
temperature.
Weigh and record each group’s beam design.
To test the beam strength, straddle each beam across a six-inch
gap.
Tie several loops of string or rope around the beam, which helps
distribute the weight and provide a place to attach the weights.
Add weight until the beam breaks. Record the maximum amount
of weight each beam held (=yield strength).
After analyzing the data- announce the winning team design as the
beam with the highest strength: beam weight ratio. Have the
winning team present their design concept to the rest of the class.
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© Math Science Innovation Center 2009
This graph can be completed by two groups or as a whole class.
Data Analysis/
Results
Conclusion /
Questions
Engineering Activity
Design
Amount of
clay used
Weight
added
Beam
Observations
weight ratio
Class discussion questions:
 Back at their desks, have the students calculate strength: beam
weight ration (ex: 120z/ 20z =6). Which beam had the highest
strength: beam: weight ration?
 Are they the same three beams that held the most weight?
 Which beams would be preferred for construction purposes?
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© Math Science Innovation Center 2009
References
Lesson was adapted from http://teachengineering.comResources for k-12, TE Activity: Breaking Beams
Math Science Innovation Center
Information on educational programs available to students, teachers and
school divisions and procedures for registering for programs.
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Engineering Activity
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© Math Science Innovation Center 2009