design of a micro-tensile test system for in situ optical ...rbb.union.edu/data/rbb summer/2015...
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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