Tensile Strength
A High School Inquiry Unit
April J. Cartwright
UNH RETE 2012
Purpose:
Completing this unit will provide an opportunity for students to explore the field of mechanical
engineering and materials science. Students will focus on developing skills in asking questions, data
analysis, and communication.
Key Words:
 Stress – The force, load, applied per unit area. Stress = load/area
 Strain – Deformation or displacement of material due to the applied stress. Strain =
∆length/initial length
 Elasticity – Complete and immediate recovery from displacement upon release of the load.
 Necking – Thinning of a material at an area where local stress is at a maximum.
 Drawing –Propagation of the neck down the length of the material
 Resilience – The amount of energy a material can absorb without suffering damage.
 Toughness – A measure of the energy needed to completely fracture a material.
 Strength – A materials resistance to fracture or excessive deformation.
 Tensile Test – A basic material test applying tension to determine the strength and how much it
will elongate.
Goals and Objectives:
By completing this lesson students will:
1. Define stress, strain, and strength. (DOK 1)
2. Explain the cause and effect relationship of stress and strain (DOK 2)
3. Formulate a testable question about stress and strain relationships and physical properties of
materials. (DOK 2)
4. Formulate a hypothesis based on research of given materials (DOK 3)
5. Collect and organize data by following experimental procedures (DOK 1)
6. Calculate stress and strain from give data. (DOK 1)
7. Graph stress and strain data using Microsoft Excel (DOK 2)
8. Compare stress and strain data from different materials (DOK 3)
9. Explain observations in terms of stress and strain and draw conclusions from data about the
physical properties of material and the behavior. (DOK 3)
10. Apply knowledge of stress and strain to the construction and testing of a composite material
(DOK 4)
New Hampshire Science Educational Standards:
 S:PS1:11:2.1 Explain that the physical properties of a compound are determined by its
molecular structure and the interactions among the molecules. (goal 3, goal 8, goal 10)
 S:SPS1:11:1.1 Ask questions about relationships among variables that can be observed directly
as well as those that cannot. (goal 3)
 S:SPS1:11:2.2 State a hypothesis and prediction based on available evidence and background
information. (Goal 4)
 S:SPS1:11:3.2 Use instruments effectively and accurately for collecting data. (goal 5, goal 10)

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S:SPS1:11:3.3 Compile and organize data, using appropriate units required. (goal 5, goal 7)
S:SPS1:11:5.1 Explain how data support or refute the hypothesis or prediction. (goal 9)
New Hampshire Technology/Engineering Student Performance Outcomes:
 A1. Select and use appropriate measuring tools to accurately gather, manipulate, and
communicate information (goal 5)
 A2. Exhibit the safe and proper selection, use and maintenance of technical equipment,
materials, and processes (goal 5)
 C1. Demonstrate those technical skills needed to find, use and communicate information
effectively in a technological world (goal 9, goal 10)
 D1. Design, develop, manage, and evaluate activities using identified problem-solving
techniques. (overall process)
Next Generation Science Standards:
 HS.PS-SPM Structure and Properties of Matter: Analyze and interpret data obtained from
measuring the bulk properties of various substances to explain the relative strength of the
interactions among particles in the substance.
Materials Needed:
 PASCO Passport Force sensor
 PASCO SPARK data collection unit
 Variety of plastic, wire, polymer, or composite samples
 Metric ruler / meter stick
 Ring stand apparatus
 Weights
 Access to computer with LCD projector
Inquiry Cycle:
The lesson follows a typical 5E science inquiry outline; however an inquiry in the classroom is often a
cyclical process, not linear. This process as outlined below should remain flexible allowing students to
move forward and backward as needed through the process. Each step is meant to build upon the
previous information that the student has acquired and eventually will lead to student driven research
and data collection. This overall inquiry is moderately student driven with substantial teacher input as
some stages and minimal teacher input at other stages. This can be adjusted based on the level of
student performance and understanding.
1. Engagement – Provide students with a copy of the handout “Tough as Nails” and the tensile
strength procedure.
 Students will watch two short video clips from the NOVA “Making Stuff” series; the clip
may be accessed at: http://www.pbs.org/wgbh/nova/tech/making-stuffcollection.html .
 As a class discuss what Mechanical Engineering is, have student brainstorm what a
mechanical engineer does, make a list or concept map on the board showing student
ideas. Added to this can be a discussion of materials science, how is materials science
related to mechanical engineering? What are the goals of materials science, what types
of materials might they be making?

Students watch a teacher demonstration of the test method for stress and strain.
Students are instructed to run a trial in groups using a provided sample so that they
gain the basic skills needed for the next steps.
2. Explore – Provide students with a copy of the handout “Project Approval Form”, they will also
continue to use the “Tough as Nails” handout.
 As a whole class brainstorm possible materials that could be tested using the method
learned previously. Materials may include different plastics such as from garbage bags,
grocery bags, etc; foil samples made from different metals such as aluminum foil or tin
foil; wires of different thickness or composition; etc
 Students split up into work groups and begin developing questions that could be asked
about the list of materials. Questions such as “Are black trash bags stronger than white
trash bags?” or “Is aluminum foil stronger than tin foil?” etc may emerge from the
discussions. Guide students to make questions specific and testable using the form
“How does the “independent variable” affect the “dependent variable”?” The question
above could be rewritten as “How does the thickness of plastic in white and black trash
bags affect the strain of the material?”
 Teams will need to research the materials they are using to find any necessary
information that is available. Groups may need to find out how the materials are
manufactured, what they are made up of, and published data on variables such as
thickness or ply. Teams will use reliable internet resources to collect information and
will interpret and cite this information in their final project. Questions may evolve or
change as groups are completing research on the materials. Groups will build an
annotated bibliography with at least 5 sources.
 Students will write a prediction and justify it with evidence from their research. A
prediction should have the form “If the (independent variable) is (change) then the
(dependent variable) will (response) because (evidence).” For example “If the thickness
of plastic is increased than the strength of the plastic will increase because of increased
area that the force is being applied to.”
 Student groups will outline the procedures being used, this will involve modifying the
original procedure given to them to suit their experimental needs, there is no need to
reinvent the wheel. Groups should also determine what data will be collected and how
it will be recorded. It will be helpful to set up data tables ahead of time.
 Students run their experiment, collect and record data. They will then be guided in
using data to calculate stress and strain and the construction of a stress-strain graph
using Microsoft Excel. Finally students will use observations, data, and graphs to draw
logical conclusions.
3. Explain – Provide students with the grading rubrics for presentation
 The students body of work will be presented as a (1) bulletin board, (2) tri-fold poster
display, (3) power point, or (4) other student designed project with prior teacher
approval. All student work displays will include an oral presentation component to the
teacher and rest of class.
 Teacher facilitated discussion or journal club discussion on the process; real world
application, challenges and successes, etc.
4. Elaborate – This is an optional addition to the inquiry experience. However, it provides a
valuable opportunity for students to apply their knowledge to a new situation. Students will
need a copy of the “Composites Challenge” handout
 Individually students will be challenged to create a composite material that as a whole
will be stronger than the components that make it up. Students will be given brief
construction guidelines and a timeframe to complete the task in. Composites will be
constructed at home but students may schedule time with the teacher during study hall
or afterschool if they need extra help or guidance.
 On the due date composites will be brought into class and the tensile strength
determined using the force sensor method.
 Students will determine how to measure if the composite really is stronger than the
parts that make it up (ie: test the raw materials then the composite).
 Incentives could help to encourage student effort and creativity: homework coupon,
silly trophies or certificates, bonus points on a test or quiz, etc.
5. Evaluate – Provide students with all grading rubrics in advance.
 Rubric (attached) for student presentation/report.
 Student written reflection on project and journal entries throughout the project.
Timeline:
The calendar below is provided to give a general overview of the flow of the inquiry. It can be
manipulated as needed. The timeline assumes that while this inquiry is ongoing other lessons will fill
the remainder of a 90 min block as needed.
Day 1 (70 min)
Day 2 (90 min)
-Video clips
-Demonstration of
tensile test
-Overview of
mechanical
engineering and
materials science
-Brainstorm
materials to test and
begin brainstorming
questions
Day 6 (90 min)
-form research
groups and refine
questions, select a
testable questions
-computer lab to
research materials,
tensile strength,
etc.
-presentation work
day and finish
graphing or analysis
as needed.
-presentations
-go over
composites
challenge, students
begin working on
composite on own
time
Day 7 (45 min)
Day 3 (45 min)
Day 4 (90 min)
-write hypothesis,
materials list,
procedure and get
approval from
teacher
-continue
background
research if needed
-run experiment
and collect data,
organize data into
tables
Day 8 (45 min)
Day 9 (90 min)
-team meeting
-students work on
own time to create
composite
- composites
challenge tests
Day 5 (90 min)
-data analysis,
creation of stressstrain curves
-groups meet to
formulate
conclusions
-make a plan for
project presentation
Day 10 (90 min)
-reflection and lab
report writing
Other Concerns:
 It can be beneficial to assign specific roles within teams to ensure engagement of all students.
 When testing tensile strength students should use appropriate PPE including goggles.
Tensile Strength
Use this form to record ideas, observations, and notes during the whole class and group brainstorming
sessions. For each section pick a different person to be the recorder for your group.
Video Notes:
What was the video clip about? What did you learn? Does the video leave you with any questions?
Mechanical Engineering and Materials Science:
As a group brainstorm what you know, or think you know, about the two topics above. Be prepared to
share with the rest of the class.
Tensile Test Demonstration:
Sketch the testing apparatus below, label as much as you can.
Describe the process of the tensile test, how is it set up? What is measured? Other observations?
Brainstorming:
In the space below record the classes’ ideas for materials to conduct tensile tests on.
Questions:
As your group comes up with questions list them all below. Then look at each question to determine if
it is testable or not. Circle the group’s top two choices of testable questions for possible investigation.
*Journal Entry – be sure that EACH member of the group writes in their journal today at the end of
class.
Project Approval Form
With your group fill out the information below and submit it for teacher approval. Once you have
approval you may begin working in the lab.
Team Members:
Research Question:
Hypothesis:
Materials List:
Safety Precautions:
Attach a copy of your detailed procedure, your data table format, and annotated bibliography as well
as any additional information you may have.
Tensile Strength
Comparing Stress and Strain
Materials:
 Force Sensor
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SPARK data collection unit
Plastic sheet cut into _________sizes
Metric ruler
Ring stand apparatus
Weights
Sample clips
Procedure:
1. Gather all of the materials listed above and set-up the system as demonstrated to you by the
teacher.
2. Cut plastic sample into dogbone shape. Template is attached. Measure the length and thickness
of the material, record.
3. Attach the plastic sample to the clips
4. Measure length of sample and record
5. Measure the mass of the empty weight container and record.
6. Hang the top of the sample from the force sensor attach weight container to bottom.
7. Measure the length of the material and the force applied by the container, record.
8. Add weight, record length of sample, SPARK will record force; record all data.
9. Continue adding weight and making measurements until plastic fails (breaks) or until a force
of 50 N is reached. This is the maximum force the sensor can handle do not add mass after 50
N is reached.
10. Calculate stress and strain using the provided formulas.
11. Graph data in excel, determine the elastic region, plastic region, and UTS as demonstrated by
the teacher.
Data:
Use the blank table below to record data – be sure to label what you are recording and the units.
Calculations:
Stress = force / area
*cross sectional area found by width multipled by thickness.
Strain = change in length / initial length
The graph to the left shows the various regions you will
need to identify on the graph you generate.
Conclusions:
1. Compare the curves for each sample.
a) Which sample had the greatest elongation?
b) Which sample had the least elongation?
c) Which sample had the highest load before breaking?
d) Which sample had the least load before breaking?
2. Does the sample with the highest load mean that that material has the greatest ultimate or tensile
strength? Why or why not? (Hint: Tensile strength is force/area).
3. Calculate the elastic modulus (Young's modulus) for each curve. This should be done by finding
the slope of the curve before the elastic limit is reached.
4. What is the relationship between stress and strain?
5. What sources of error exist in this experiment? Discuss the methods you could use to avoid
them.
The Composites Challenge
Objective: Students will design and conduct tensile tests on a new composite material.
Before you begin be sure you can answer the following questions, you will need to do research on
composite materials using reliable internet resources.
1. What is a composite?
2. Identify several types of composites. How are they made? What are they made out of? What
are they used for?
3. What are several advantages and disadvantages of composite materials?
Brainstorm:
With your group brainstorm possible materials and methods to use to make your composite, you may
wish to include sketches or diagrams.
Design and Build:
As a group agree on your materials and method for constructing the composite. Have your plan
approved by the teacher and then begin working.
Data Collection and Analysis:
Test your composite material following the same procedure as used for the plastic samples. Be sure to
record all data and construct the appropriate graphs. How can you determine if your composite is
actually stronger than the parts that make it up?
Final Report:
Your final report will be submitted as a formal lab write-up. Please refer to the rubrics for this. The
team will submit one lab report but all should participate in constructing it.
In addition each team member will submit a written reflection about the process, refer to the rubric
for reflection writing.
Tensile Strength Lab Report
Outline
Each section below should be in a separate heading. How you organize within each section is up to
you. Do not just list answers to questions, be sure to write logical and cohesive paragraphs that
address the required information. Formatting is included on the grading rubric!
Introduction:
 Background on materials science and mechanical engineering
 Define all necessary vocabulary
 State question and hypothesis - for both initial trials and composite challenge
Materials and Procedure:
 List all materials in bulleted format
 List procedure in a number step by step format; separate procedure for initial trials and
composite challenge if needed.
Data:
 Provide data tables and graphs – with all needed titles and labels.
 Each figure should have a summarizing statement
Discussion:
 Calculations of stress and strain for each material
 Written explanation of the trends or patterns you observed
 What assumptions can you make about the structure of the material(s) you tested? Are your
results supported by any published data? How does chemical bonding / atomic structure affect
the strength of your material?
 Is your composite stronger than the non-composites that make it up? How do you know? Why
do you think this happens? Are your results supported by any published data?
Conclusions:
 Summarize the key points presented in the paper - was your hypothesis supported by the data?
Do you have any errors to account for?
 Future work – what would be the next steps? What questions do you have?
Tensile Strength Unit Check Brick
Keep this form in your group’s folder or at your work station. When a task is completed check off the
item and sign that you have turned in or completed the task. Be sure to also have the teacher initial
that they have seen the work or you have handed it in to them.
Unit Requirement
Brainstorming Form
Project Approval Form
Annotated Bibliography (attached
to project approval)
Procedure (attached to project
approval)
Data table design (attached to
project approval)
Calculations of stress and strain
Stress-Strain Graph with labels
Presentation to class of results
(poster, PowerPoint, etc.)
Composite material constructed
Date Complete
Team Member Signature
Teacher Initials
Composite material stress and
strain calculations
Composite material stress-strain
graph with labels
Final lab report (see rubric)