DESIGN AND DEVELOPMENT OF AN ECONOMICAL TORSION TESTING MACHINE

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DESIGN AND DEVELOPMENT OF AN ECONOMICAL TORSION
TESTING MACHINE

• by
• Glenn Vallee, Ph.D., P.E.
• And
• Robert Short
• Mechanical Engineering Department
• Western New England College

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Project Objectives

• Design and build a torsion testing machine
  capable of performing the ASTM Torsion Test
• Machine must measure material properties to
  within 5 of published data
• Machine must be affordable

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Torsion Testing Apparatus

• Experimentally determines torsional shear
  properties of materials
• A cylindrical test specimen is twisted until
  failure
• Applied torque and angle of twist are recorded
• ASTM Standardized Test Method Used- Specifies
  Test Procedure / Specimen Geometry

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Design Constraints

• Machine must be capable of fracturing a steel
  test specimen
• Specimen diameter to be 3/8 inch to allow
  examination of fracture surfaces- ASTM therefore
  requires a specimen length of 6 inches to
  meet the min length/diameter ratio
• Torque and angle of twist measuring devices to be
  easily accessible to students

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Design Constraints

• Machine must produce measurements within 5 of
  published ASTM results
• Budget allocation of 500
• Many Years of Service!!!

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Determination of Shear Properties

• Elementary mechanics theory used to relate
  applied torque, T to shear stress, t using
• Eq. (1)

where ? radius of the specimen cross section
J polar moment of inertia of cross
section

• Shear strain ? is calculated using
• Eq. (2) ? ??/L
• where L specimen length ?
  angle of twist

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Determination of Shear Properties

• Shear Modulus G is determined by finding the
  slope of the shear tress-strain diagram
• Shear modulus may also be calculated using

Eq. (3)
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Design Torque and Angle of Twist Requirements

• Equation (1) was used to estimate the torque
  required to yield a C1018 plane carbon steel test
  specimen in torsion
• 3000 in-lb would be required to fail C1018
  material at constant rotational velocity
• Experiments were performed using aluminum to find
  required angle of twist (10 revolutions)

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Design Layout
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Drive Train

• A DC motor with an integral gear reduction and
  speed controller was used
• A sprocket set having a 61 gear ratio developed
  required torque

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Frame Design

• Two inch square steel channel was welded
  together to form the frame

Base
Frame / Motor Sub Assembly
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Measurement of Torque

• A torque gauge was fitted to the fixed hub

Gage mounted on a 45 Angle
Torque Gage
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Measurement of Torque

• Strain Gauge aligned with direction of Max
  Principle Stress

(kpsi)
max
s2
State of Pure Shear
2?
s1
s2
s (kpsi)
45
s1
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Measurement of Angle of Twist

• A potentiometer was mounted to a wheel which
  contacted the rotating hub.

Weight
Potentiometer
Wheel
Sprocket
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Chuck Alignment

• A T-slide was used to prevent development of
  axial loads and to aid in alignment

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Torque Calibration

• A weighted lever system was used to calibrate
  the torque gauge

Gage
Fabricated Torque Wrench
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Torque Calibration Curve
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Complete Assembly
Strain Gauge Leads
Potentiometer Leads
Motor Speed Control
Power Switches / LEDs
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Performance

• Data Collection with Lab VIEW
• Testing of 1018 Cold Drawn Steel
• Shear modulus measured as 10.7 Mpsi, 3 lower
  than the published value
• Testing of 2014 Aluminum
• Shear modulus measured as 3.7 Mpsi, 5 lower than
  the published value

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Budget Analysis
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Integration Into the ME Curriculum

• Torsion machine has been integrated in two ways-
  ASTM torsion experiment has been included in
  the junior laboratory sequence- design and use
  of the torsion machine is introduced in the
  sophomore Mechanics of Materials course

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Junior Laboratory Experience

• Students examine the torque cell and calculate
  its limiting torsional strength
• Students create calibration curves for the torque
  cell and rotational potentiometer
• Steel and aluminum specimens are tested o failure
  and the results are compared to published data

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Mechanics of Materials Course

• Students examine the torque cell and calculate
  its limiting torsional strength
• ASTM torsion test is performed in class
• Students determine the shear stress-strain
  diagram for steel and aluminum and determine
  their shear modulii
• Shear failure surfaces are examined

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QUESTIONS?