UAA School of Engineering

1
Elastic Stress-Strain Relationships in Simple
Tension Testing

• UAA School of Engineering
• CE 334 - Properties of Material
• Lecture 4

2
Static Simple Tension Test

• Static Tension Test A prepared specimen is
  subjected to a gradually increasing (i.e.,
  static) uniaxial load until failure occurs.
• Simple Tension Test The operation is
  accomplished by gripping opposite ends of the
  piece of material and pulling it apart.
• Purpose
• To evaluate fundamental mechanical properties for
  use in design
• To predict performance of materials under all
  loading conditions.

3
Simple Tension Test Setup
4
Rebar Test Set up

• Grip wedges designed specifically for testing
  reinforcement bars
• Extensometer with 200 mm or 2 inches gage length

5
The 1st Lab Tension Test

• The objective of the Lab Exercise
• The student is expected to become familiar with
  the essential features of tension test procedure
  and to be able to properly interpret the
  resulting data, for example
• Modulus of elasticity
• Proportional limit
• Yield point
• Modulus of resilience.

6
Specimens

• Cross Section round, square, or rectangular.
• Shape The central portion of the length is
  usually of smaller cross section than the end
  portions, in order to cause failure to occur at a
  section where the stresses are not affected by
  the gripping device.
• Gage Length is the length over which elongation
  or extensometer measurements are made.

7
Standard Metal Tension Specimens
8
Typical Tension Specimens
9
Measurement of Test Specimens

• Do you know how to determine the cross sectional
  dimensions of the test specimen?
• Do you know how to use a vernier caliper?

10
Data Acquisition and Reduction

• Data Measured by Hands
• Diameter of the specimen Area of
  cross section A
• Data Recorded from MTS Machine
• Applied force Load cell P
• Strain readings Extensometer ?
• Data Reduction
• ? P/A

Stress-strain Curves
?
11
Typical Stress-Strain Diagram for Hot Rolled Steel
by true stress
by engineering stress
Plastic Range
Elastic Range
12
Elastic Strength
13
Yield Points - for Hot-Rolled Steel

• Upper Yield Point The crest of the first peak in
  the stress-strain diagram of mild steel.
• Lower Yield Point The bottom of the first lower
  peak in the stress-strain diagram of mild steel.
• Yield Point The upper yield point.

14
Aluminum Alloy Tension Test
15
Cast Iron Tension Test
16
Offset Method-Generic Yield Points

• Used to determine the Proportional (or Elastic)
  Limit and Yield Strength of a non-linear
  material.
• By finding the intersection of the stress-strain
  curve of a non-linearly material and the offset
  line.
• Common offset values are .002 and .0035.

17
Non-Linear Elasticity
offset line
offset
18
Work and Energy

• Work done on an elastic body is stored as Strain
  Energy and can be recovered mechanically.
• Work done on a plastic body is converted into
  non-mechanical energy
• Heat, Sound,

Listen to the sound, when the specimen is broken.
Touch the necking material to feel the heat
19
Measurement of Strain Energy
P
?L
Strain energy due to ?? (??)(??) area under ??
in ? ? curve
P
20
Calculation of Strain Energy in an Elastic Range

• Elastic Resilience
• The amount of energy absorbed in stressing a
  material within the elastic limit.
• It is represented by the area under the
  stress-strain curve within the elastic range.

21
Modulus of Resilience

• Modulus of Resilience The energy stored per unit
  of volume at the elastic limit.
• It is represented by the maximum area under the
  stress-strain curve within the elastic range.

22
The End

• Lab 1 Tension Testing this week!
• Read handout and ASTM references in preparation.