Poster Design & Printing by Graphic Arts Center

Design and Fabrication of a Micro-Tensile

Test System for In Situ Optical Microscopy

Introduction and Background

.

Data Acquisition System

A load cell measures the force on one crosshead (and thus on the

specimen) while displacement is measured by tracking the crosshead

with a linear displacement sensor. Both sensors were calibrated to relate

voltage output to displacement and force. Data is recorded on Matlab in

real-time using a Graphical User Interface. The system is also compatible

with StrainSmart software and hardware.

Final Design

The Stage Specifications are:

• 100lb Load Capacity

• 32.5cm*18.3cm*2.7cm Footprint

• Submicron Resolution

• Low Force and Displacement Noise

• Coarse and Fine Strain Adjustment

• StrainSmart and Matlab Compatible

• $1800 Price Tag (Including Sensors)

Conclusions and Recommendations

Acknowledgements

• Ronald B. Bucinell, Ph.D., P.E.

• Paul Tompkins

• National Science Foundation CMMI-1362234

• Student Research Grant

• Rhonda Becker

Senior Project-Mechanical Engineering-2016

Fig 1: Tensile Stage SolidWorks Design

Diminishing nonrenewable resources such as petroleum used in the

manufacturing of synthetic plastics and the carbon footprint of the

manufacturing processes have prompted interest in finding greener

alternatives such as biomaterials. To successfully use them, it is crucial to

characterize their mechanical behavior, and understand the microstructural

properties underlying such behavior. This knowledge can also help in

successfully manipulating the microstructure of biomaterials to obtain desired

mechanical properties.

To perform microscopic characterization, the material is loaded while

observing its microstructure under a microscope. Micro-tensile stages are

miniature versions of Universal Testing Machines that can be placed inside or

under different types of microscopes. Currently, there is no capability to

perform such tests as the tensile stage is too big to fit under the microscope.

Therefore, the objective of this project was to design and build a new tensile

stage that fits under the Olympus BX-15 optical microscope, and can

accommodate the 1000x optical lens and different test fixtures.

The final SolidWorks design that

was used in the fabrication and

assembly of the new tensile stage

is shown in Figure 1. The design

incorporates commercial drive

components and CNCed

aluminum parts. To stretch the

sample, the user turns the dial and

the gear train translates the motion

into symmetric linear crosshead

displacement. Figure 3 is the final

manufactured stage.

Fig 3: Fabricated Tensile Stage Fig 2: Microscope Integration

y = 2277.2x + 1681.7 R² = 1

-1000

0

1000

2000

3000

4000

5000

6000

7000

8000

-1 -0.5 0 0.5 1 1.5 2 2.5

Mass(g

)

Voltage (V)

Mass vs Voltage for 100lb Load Cell

Fig 5: Block diagram of DAQ system (left) and

data collection algorithm (right)

Fig 5: Setup for load cell calibration (left) and the

resultant calibration curve(right)

To test the functionality of the stage, a tensile test was conducted on a

rubber specimen to obtain the force versus displacement curve shown

below. The second curve was obtained using StrainSmart software and

hardware, while driving the stage with a drill instead of a hand dial to

evaluate the concept of a motorized stage.

Fig 6: Force and Displacement curves for a silicon rubber specimen on Matlab and StrainSmart

A low cost tensile stage that is compatible with the microscope in

the Materials Lab was successfully designed and built. While the

system functions well, the addition of a motor will reduce noise

associated with moving the dial as well as prevent the discomfort on

the hand of the operator. Due to the stage’s weight, a multi axis

platform will make it easier to move the stage instead of using the

microscope platform.

Fig 3: Noise test on the load and displacement

sensors

Zibusiso Dhlamini

Advisor: Professor Ronald B. Bucinell, Ph.D, PE.