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Raman Spectrometer Micro-Load Frame

SPRING 2016 MAE 156B SPONSORED PROJECT

UNIVERSITY OF CALIFORNIA, SAN DIEGO

SPONSORED BY KENNETH J. LOH (Ph.D.), ARMOR LAB

Background

Thin-film nanocomposites exhibit changes in electrical conductivity when subjected to mechanical strains and have been shown to be able to detect damages in various aerospace, mechanical, naval, and civil engineering structures. In his ARMOR (Active, Responsive, Multifunctional, & Ordered-materials Research) lab, Dr. Kenneth Loh is investigating thin-film carbon nanocomposites to better understand the mechanism as to why the materials change their electrical conductivity. The purpose of this project was to develop a micro tensile load frame that could fit within the test chamber of a Raman NRS-5100 spectrometer to subject thin-film test specimens to known strains while under the observation of the Raman spectrometer. With this testing setup, the effects of these strains could be observed on the micro and nano scale in order to better understand the mechanism behind the change in electrical conductivity. With these results, it would be possible to reproduce specific material properties to detect strain.

JASCO Raman Spectrometer NRS-5100

Chamber of Raman Spectrometer NRS-5100

Objectives

The objective of this project was to design a load frame that could help the researchers using a Raman spectrometer (JASCO NRS-5100) take data while their samples are strained. In order to achieve this, there were a set of required functionalities to be fulfilled. The device had to fit inside the spectrometer and under the lens. The sample needed to be strained in controlled measurable steps for researchers to perform accurate analysis on them. Also the nanocomposites are placed on paper to be strained, therefore there needed to be sufficient clamping force to hold them and to perform the displacement. Below, these functional requirements are listed in more detail:

Overall size of 300(L) x 135(W) x 29(H) mm
Minimum displacement resolution of 25 μm
Ability to hold sample sizes of 10(L) x 5(W) mm, with thickness of up to 0.5 mm
Ability to produce necessary force to strain printer paper (σpaper ≃ 350 kPa)

Cross Section View of the Load Frame (Isometric View)

Description of Final Design

The final design of the load frame consists of two stationary blocks of aluminum and a non-stationary block in the middle. One of the stationary blocks serves as a linear actuator mount and the other stationary block holds a linear potentiometer. Once the sample is placed in the clamps between the moving block and the potentiometer block, the linear actuator will pull the moving block to create displacement in the sample. The desired displacement is input by the user through a graphical user interface (GUI) created using Visual Studio. On each side of the load frame, acrylic 'spines' are used to avoid any twisting motion while the load frame is being moved or transported. For a more detailed explanation of the final design, please refer to the Final Design page.

Final design of micro-load frame

Components

Linear Actuator

Linear Potentiometer

Mounting Blocks

Grips

Acrylic Spines

Graphical User Interface

Arduino Uno, ADC shield and motor driver shield

3D-printed electronics housing

Summary Of Performance Results

Many performance tests were used to determine the functionality and accuracy of this micro-load frame design. After and initial prototype test, it was determined the potentiometer was very linear with a correlation coefficient of R= 0.99992. However, there was significant noise of about 18 micrometers possibly do to poor wiring, actuator vibration, or general circuitry as the noise was on the order of only a few micro-volts. The final achieved resolution for this load frame was 3.175 µm/step using the stepper motor with an overall accuracy of ± 3 µm. Allowable sample sizes can range from 30-45 mm long with a width of up to 16 mm and 2 mm thickness. The grips have sufficient clamping force (over 250 N) to hold samples in place under tension and the load frame is able to produce tension forces up to 50N. Finally, the overall dimensions of the load frame were 243x130x29mm (LxWxH), with additional clearance near the sample to accommodate the spectrometer microscope head.

Final Prototype Performance Testing

The following videos show the load frame being tested by straining a sample to failure. This is an extreme condition since the samples will not be strained to failure in lab analysis and the input strains will be controlled and planned. The first two videos show the sample being strained from different angles to clarify the process. In both cases the sample fails near the grips. The third video demonstrates a test to verify varying sample thickness and also force capabilities of the linear actuator. In this test, two identical samples were strained simultaneously. It can be seen that both samples fail, followed by a slight jerk in the middle block.

Early Prototype:

In earlier stages of this project, an acrylic frame was developed in order to be able to test the motion of the linear actuator and measure the response of the linear potentiometer. This acrylic frame was the result of quick prototyping with the help of a laser-cutter (LaserCAMM). This frame allowed for mounting the actuator and the potentiometer in varying positions along the frame for the ease of testing purposes.

Executive Summary:

For a link to the current Executive Summary click here: Executive Summary Link.

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