# 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

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
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 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

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

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

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
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)

Design Layout

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

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

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
A potentiometer was mounted to a wheel which contacted the rotating hub. Weight Potentiometer Sprocket Wheel

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

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

Torque Calibration Curve

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

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

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

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
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
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

QUESTIONS?

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