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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. Project Objectives. Design and build a torsion testing machine capable of performing the ASTM Torsion Test

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design and development of an economical torsion testing machine

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

project objectives
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
torsion testing apparatus
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
design constraints
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
design constraints1
Design Constraints
  • Machine must produce measurements within 5% of published ASTM results
  • Budget allocation of $500
  • Many Years of Service!!!
determination of shear properties
Determination of Shear Properties
  • Elementary mechanics theory used to relate applied torque, T to shear stress, τusing
  • Eq. (1)

where ρ = radius of the specimen cross section J = polar moment of inertia of cross section

  • Shear strain γ is calculated using
  • Eq. (2) γ= ρθ/L
  • where L = specimen lengthθ = angle of twist
determination of shear properties1
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)

design torque and angle of twist requirements
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)
drive train
Drive Train
  • A DC motor with an integral gear reduction and speed controller was used
  • A sprocket set having a 6:1 gear ratio developed required torque
frame design
Frame Design
  • Two inch square steel channel was welded together to form the frame

Base

Frame / Motor Sub Assembly

slide12

Measurement of Torque

  • A torque gauge was fitted to thefixed hub

Gage mounted on a 45° Angle

Torque Gage

measurement of torque
Measurement of Torque
  • Strain Gauge aligned with direction of Max Principle Stress

(kpsi)

max

σ2 =

State of Pure Shear

σ2

σ1

σ (kpsi)

45°

σ1 =

measurement of angle of twist
Measurement of Angle of Twist
  • A potentiometer was mounted to a wheel which contacted the rotating hub.

Weight

Potentiometer

Sprocket

Wheel

chuck alignment
Chuck Alignment
  • A T-slide was used to prevent development of axial loads and to aid in alignment
torque calibration
Torque Calibration
  • A weighted lever system was used to calibrate the torque gauge

Gage

Fabricated Torque Wrench

complete assembly
Complete Assembly

Strain Gauge Leads

Potentiometer Leads

Motor Speed Control

Power Switches / LEDs

performance
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
integration into the me curriculum
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
junior laboratory experience
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
mechanics of materials course
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