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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 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, 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

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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 6:1 gear ratio developed required torque

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**Frame / Motor Sub Assembly**

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

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**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

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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 =

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**Measurement of Angle of Twist**

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

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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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**Fabricated Torque Wrench**

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 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

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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?

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