1. DESIGN AND DEVELOPMENT OF AN ECONOMICAL TORSION TESTING MACHINEby
Glenn Vallee, Ph.D., P.E.
And
Robert Short
Mechanical Engineering Department
Western New England College

2. 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

3. 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

4. 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 inches to meet the min length/diameter ratio
Torque and angle of twist measuring devices to be easily accessible to students

5. Design Constraints
Machine must produce measurements within 5% of published ASTM results
Budget allocation of $500
Many Years of Service!!!

6. Determination of Shear Properties
Elementary mechanics theory used to relate applied torque, T to shear stress, τ using
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 length θ = angle of twist

7. 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)

8. 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)

9. Design Layout

10. 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

11. Frame / Motor Sub Assembly
Frame Design
Two inch square steel channel was welded together to form the frame
Base
Frame / Motor Sub Assembly

12. Gage mounted on a 45° Angle
Measurement of Torque
A torque gauge was fitted to the fixed hub
Gage mounted on a 45° Angle
Torque Gage

13. Measurement of Torque
Strain Gauge aligned with direction of Max Principle Stress
(kpsi)
max
σ2 =
State of Pure Shear 2Ө σ2 σ1
σ (kpsi)
45°
σ1 =

14. Measurement of Angle of Twist
A potentiometer was mounted to a wheel which contacted the rotating hub.
Weight
Potentiometer
Sprocket
Wheel

15. Chuck Alignment
A T-slide was used to prevent development of axial loads and to aid in alignment

16. Fabricated Torque Wrench
Torque Calibration
A weighted lever system was used to calibrate the torque gauge
Gage
Fabricated Torque Wrench

17. Torque Calibration Curve

18. Complete Assembly Strain Gauge Leads Potentiometer Leads
Motor Speed Control
Power Switches / LEDs

19. 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

20. Budget Analysis Item Description Manufacturer Mfg. # Vendor Vendor #
Quantity
Cost Ea. ($)
Total Cost ($)
DC Motor
Dayton
4Z530
Grainger
4Z531 1
258
DC Speed Control
Dart Controls
125DV-C-K
2M510 77
2 inch Sprocket
US Tsubaki
50B9F
6L927 11
12 inch Sprocket
Browning
50Q60
1L213 93
Chain (10 feet)
50TW10
2W095 34
Potentiometer
EIT
MW22B-10-2K
Newark InOne
83H7568 10
Drill Chuck
Jacobs
30602
McMaster
3094A17 2 19 38
Neon Lamp Assembly
Radio Shack 4
Dual Binding Post 5
Final Cost ($)
534

21. 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

22. 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

23. 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

24. QUESTIONS?