DESIGN AND DEVELOPMENT OF AN ECONOMICAL

TORSION TESTING MACHINEby

Glenn Vallee, Ph.D., P.E.And

Robert Short

Mechanical Engineering DepartmentWestern 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 6 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

J

Tρτ =

• Elementary mechanics theory used to relate mechanics theory used to relate

applied torque, T to shear stress, applied torque, T to shear stress, ττ usingusing

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

GJ

TL=θEq. (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

FIXED HUB

SPROCKET

ROTATING HUB

T-SLIDE

STRAIN GAGE

CHUCKS

UNIFORM BASE PLATE

SPECIMEN

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

Base

Frame / Motor Sub Assembly

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

Gage mounted on a 45° Angle

Torque Gage

Measurement of Torque• A torque gauge was fitted to the fixed hub

Measurement of Torque

τ

τ

σ (kpsi)

(kpsi)

σ2 =

σ1 =

τ

τ

2Ө

• Strain Gauge aligned with direction of Max Principle Stress

45°

max

σ1σ2

State of Pure Shear

τ

Measurement of Angle of Twist

Potentiometer

Weight

WheelSprocket

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

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

Torque Calibration

Fabricated Torque Wrench

Gage

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

Torque Calibration Curve

Complete Assembly

Potentiometer Leads

Motor Speed Control

Power Switches / LEDs

Strain Gauge Leads

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 1 258 258

DC Speed Control Dart Controls 125DV-C-K Grainger 2M510 1 77 77

2 inch Sprocket US Tsubaki 50B9F Grainger 6L927 1 11 11

12 inch Sprocket Browning 50Q60 Grainger 1L213 1 93 93

Chain (10 feet) US Tsubaki 50TW10 Grainger 2W095 1 34 34

Potentiometer EIT MW22B-10-2K Newark InOne 83H7568 1 10 10

Drill Chuck Jacobs 30602 McMaster 3094A17 2 19 38

Neon Lamp Assembly Radio Shack 2720712 Radio Shack 2720712 1 4 4

Neon Lamp Assembly Radio Shack 2720708 Radio Shack 2720708 1 4 4

Dual Binding Post Radio Shack 2740718 Radio Shack 2740718 1 5 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?