Design of A Micro-Tensile Test System for In Situ Optical ...rbb.union.edu/data/RBB Summer/2015...

Poster Design & Printing by Graphic Arts Center

Design of A Micro-Tensile Test System for In Situ Optical Microscopy Applications

Zibusiso Dhlamini `16

Advisor - Ronald B. Bucinell, Ph.D, PE.

Introduction and Background

A joint effort is underway between researchers at Union

College and RPI to develop sustainable materials that can

replace synthetic plastics and organic fibers. This effort is

an attempt to reduce reliance on diminishing and

increasingly valuable nonrenewable petroleum supplies.

Materials development requires that the performance of the

materials, their composites, and the interfaces between the

constituents of the composite be characterized so

designers can model their performance in structures.

Characterization takes place at many levels, in this project

the concern is with microscopic characterization.

To perform microscopic characterization the materials must

be loaded while being observed under a microscope. At

Union College there is no current capability to perform this

type of characterization and therefore a tensile stage that

can fit under the existing microscope in the Mechanics Lab

needs to be designed and built.

Abstract

A preliminary design was started for a tensile

stage that fits between the objective lenses and

stage of the Olympus BX-15 optical microscope

located in Mechanics Lab in Butterfield 101.

This stage will be used to assist in the

characterization of the constituents that are

being used in the development of sustainable

composite materials.

Design Objectives

The objective I had was to build the microscope

that:

1. Could fit under optical microscope in the

Mechanics Lab

2. Used similar components (motor, LVDT, gear

ratios) to the existing tensile stage so that the same

controller could be used.

3. Designed to accommodate the existing range of

load cells used by the existing tensile stage.

4. The Tensile stage profile needs to be small

enough to accommodate the 1000x optics

5. Enable the use of multiple test fixtures including

tension, compression, and bending.

6. Allow manual and motor displacement control

Design

Mechanism

• Motor and hand crank transfer torque to worm shaft

• Worm shaft has right hand thread that drives two

worm gears attached to lead screws

• Worm drive multiplies input torque by 30

• Dual lead screws have left and right hand thread that

drives cross head in opposite directions with a force of

362.5lb each

Sensors

• Interchangeable load cells measure the force on the

grips

• Linear Displacement Sensor with maximum

displacement of 25mm track crosshead motion

• Bumper switches prevent crosshead overshoot

Grips

• Revolute joints eliminate eccentric loading

• Interchangeable grips allow various tests to be

conducted

Design Validation

Force Analysis

• Lead screws with a diameter of 10mm, 2mm pitch, and efficiency of 0.25 require

2.86Nm input torque to raise a load of 3200N (725LB)

• The 30:1 reduction worm drive requires a motor input torque of 0.115Nm (assuming

60% efficiency). The motor selected has a stall torque of 0.138Nm (less torque than

twisting a door knob)

Finite Element Analysis (FEA)

• An FEA study was carried out on SolidWorks to ensure that the crosshead assembly

would not fail under a maximum tensile load of 725lb

• The minimum Factor of Safety (FOS) is 4, therefore non of the components will yield

Conclusions/Future Work

In conclusion, a miniature tensile testing machine compatible

with the existing optical microscope in the lab (Figure 4) has

been designed. More work needs to be done to stabilize the

system and reduce vibrations. The next step is to purchase the

mechanical components and get the machined parts fabricated

at the Union College Engineering Lab. Assembling and testing

will commence in the Fall as part of a senior project. In-situ

stress tests will help us better understand how the

microstructure of biopolymers affects their bulk mechanical

properties.

Acknowledgements

• Ronald B. Bucinell, Ph.D., P.E.

• National Science Foundation CMMI-1362234

• Innotech International LLC

• Ecovative Design LLC

Summer 2015 Research

Figure 4 shows how the tensile stage will be secured on a Thorlabs translation

stage. This stage will then be screwed onto a metal block instead of an air table.

Figure 3 shows FEA results show the factors of safety of

the crosshead and grip assembly range from 4 to 20.

Figure 2 shows a SolidWorks model of the tensile stage

System Integration

To achieve 3D translational

motion, the stage will be mounted

on a Thorlabs manual stage

(Figure 4). To stabilize the

structure and prevent tipping, the

manual stage will be bolted onto a

block of metal placed on the table.

Due to the likelihood of motor

induced jerks on a cantilever

structure, the microscope stage

may be used to balance the

hanging part of the tensile stage

once the desired height is

achieved.

Figure 1: The optical

microscope in the

Mechanics Lab