Executive Summary s20

Abstract

Important research can be conducted using a Raman Spectroscope combined with a fiber stretching instrument to study the molecular properties of fiber silk. Manning Applied Technologies (MAT) has a potential client interested in employing them to provide the instruments to conduct this research. MAT needs to know the best design for a fiber stretching instrument and requires proof as to why it is the best design. This feasibility study presents the best concept designs to solve all the major problems involved with the design of the instrument.

Executive Summary

Important research can be conducted using a spectroscopy lasers combined with a fiber stretching instrument to study what gives fiber silk its strong properties. Manning Applied Technologies needs to know from my capstone team the best design for a fiber stretching instrument and wants proof showing why it is the best design. This design needs to solve the problems of how to attach the fiber, how to stretch the fiber, and how to measure the force on the fiber. The team developed a working concept design to solve all of these problems. The team divided the design of the stretching instrument into three subsystems: the attachment system, the motion system, and the measurement system.

The design of the fiber attachment was the first step and everything else built off that. The team thought of several ideas for how to attach the fiber and decided the JB-Weld worked best. The JB-Weld attaches the fiber to precision alignment rods, which are held in place with a transfer tool and a jig.

The team developed three designs for the motion system that were all drawn in SolidWorks to get a better idea of how they would work and have a better representation to present. The recommended right hand, left hand screw design moves the fiber from both ends at the same speed at the same time with a single input, which will make sure the laser measures the same spot during the entire test.

The team did thorough research to find the best value for the required measuring instruments. The recommended load cell costs $625.00 and measures in the correct range with a 0.05% accuracy. The recommended caliper costs $119.00 and measures with an accuracy of 0.02mm, which meets the design constraints. The total combined cost of the recommended systems is $1,595.

1.0 Introduction

Background

Spider silk fibers possess extraordinary mechanical properties. (Sirichist, Young, and Vollrath, 1999, p. 1) Not only are they as strong as many high performance synthetic polymer fibers, but they also have extremely high elasticity, meaning they can absorb more energy than fibers commonly used in industrial applications today (like concrete, fiberglass, and other composites). Research of these fibers on the molecular level can lead to great advancements in creating stronger new synthetic fibers. It has been shown that well-defined Raman spectra can be obtained of the fibers. Analyzing the shift of the Raman spectra of these fibers under deformation can lead to a greater understanding of the micromechanics involved within the fibers. The spectra shift linearly with respect to stress as the fiber is deformed, indicating the fibers deform on the molecular level as the fiber as a whole deforms. (Sirichist, Young, and Vollrath, 1999, p. 1)

Problem

The engineering team comprised of Peggy Brown, Anna Henson and David Denton was given the task to design an apparatus that can stretch the fiber specimen specified by Michel Pezolet to a specified range of forces while also withstanding a wide variety of humidity effects. This system was also required to include a method to load the fragile fiber into the fiber stretching apparatus without breaking or prematurely stressing it.

Objectives

The purpose of the project is to design, fabricate, and test a system that stretches a thin fiber in the appropriate manner by April 2004. This must also include a way to prepare the fiber specimen without affecting it negatively.

Scope

The team will not be required to construct a system that causes climate control. Little to information is known about the fibers being tested. The only information given was the dimensions of the fiber, that it is very fragile, and the effective force is anywhere from 0 to 50 mN.

Methods

The project came together by first interviewing Manning Applied Technologies to fully understand their wants and needs. Then the team conducted extensive research to aid the design process. With this research the team then compiled a number of different prototype schematics. The decidedly best version of the schematics was then constructed as a first prototype. After cycling the prototype through an iterative and testing process, the changes to the apparatus produced a better system. After a comprehensive iteration process, the best product was then chosen and presented to Manning.

2.0 Problem Definition

The main problem of designing a fiber testing instrument was decomposed into several sub-problems that were designed as separate systems and later integrated for one final product.

Systems Description

1.  The Attachment System must provide the necessary setup for ease of placement and removal of the fiber specimens while not damaging them. The object to which the fiber attaches must also allow for constraining the fiber in all directions during stretching.

2.  The Motion System must stretch the fiber so the laser can measure the molecular properties of the fiber under strain. The stretching needs to be symmetric so the sample spot does not move.

3.  The Measurement System must measure both the force applied to the fiber and how much the fiber stretches so the stress in the fiber can be compared with the Raman data.

Criteria

To be acceptable, the instrument must satisfy the following requirements:

1.  Protect the fiber from damage during set up and testing.

2.  Apply a deflection to the fiber while holding the test point stationary

3.  Measure the load on the fiber in the 50 mN range.

4.  Measure the deflection of the fiber to an accuracy of 0.01 mm.

5.  Allow the laser microscope to reach the focus distance of 4.7 mm from the specimen with transparent material in between.

6.  Cost less than $1500 for parts.

3.0 Fiber Attachment

The first step in the fiber stretching process is to attach the fiber. The fiber stretching system can be separated into two parts: how to attach the fiber and what to attach it to. The various methods of attaching the fiber combine with different devices to attach the fiber to. The decision about how to attach the fiber was made first and then the device to attach it to was developed to combine best with the method of attachment.

3.1 Concepts considered

Bonding agent

1.  Knot: The user threads the fiber in at the through-hole of a rod, and then make a knot. The fiber would then wind around the rod before going to the other rod with a symmetrical configuration.

2.  Magnets: The user places the fiber in a folder piece of paper. Position two magnets outside the paper so they clamp onto the fiber and paper. Then slide the magnets toward the edge of the paper and off so they are now only clamped to the fiber.

3.  Clamps: The user places the fiber in special clamps designed hold the fiber. The design has not been developed.

4.  3M Sticky Tape - The user places the fiber on the sticky surface and wrap several times. Then clamp two pieces together on the attachment device.

5.  Elmers: The user applies Elmer’s glue to the attachment device, place the fiber gently in the adhesive and wraps twice before going to the other side with a symmetrical configuration, and finally applies Elmer’s again over the wrapping.

6.  JB Weld: The user applies the JB weld in the same manner as the Elmer’s glue. It is an epoxy that comes in two tubes, one with a white paste and one with a dark gray paste. You have to mix the two in equal parts before applying it. It stiffens to the unusable point within 5 minutes and takes 4 to 6 hours to set.

7.  Hot Glue: Use hot glue in the same manner as the Elmer’s glue. The gun heats the glue in about 5 minutes and then it is quick to use. The glue sets in less than a minute, so the fiber must be placed in its final position quickly.

8.  Hot Glue: Use hot glue in the same manner as the Elmer’s glue.

9.  Scotch Tape: Use the Scotch tape to adhere the fiber to the attachment device.

Attachment device

Two attachment device ideas were prototyped to combine with adhesive to test which one would work better:

1.  Window: A cardboard rectangle with a smaller rectangle cut out of the middle holds the fiber in place on either end where the fiber wraps around the cardboard. Precision slits or grooves can be cut into the part where the fiber meets the inner edge of the cardboard.

2.  Precision Alignment Rod: Figure 1 shows the layout of the rods. The user applies the fiber to the rod wrapping around the threads and coming off the rod in a precision groove. The groove will be machined at an exact length from the point where the rod attaches to the stretcher to keep the fiber perpendicular. The shape of the groove allows different sized fibers to naturally fit to the bottom of the groove. Then the fiber leads to another symmetrical rod where the fiber aligns in the groove first and then wraps in the threads.

3.2 SOLUTION EVALUATION

Bonding Agent

Table 1 shows the results of prototyping and testing of each solution for how to attach the fiber. The different categories are weighted for their importance to the end results of the project using a 1-5 scale, one being least important, five being most important. Then a score for how well the option satisfies the need based on testing is assigned. The weight of each need is multiplied by the score given for the each option. This product is then summed and the highest total yields the best option.

The strength and fiber damage received the highest weight because if any of these categories were to fail, the experiment would fail. The strength refers to how much force can be applied to the fiber without slippage.

1. Knot: The fiber is extremely difficult to manipulate, so tying a knot even with the use of adhesive proved frustrating and almost impossible.

1. Magnets: The magnets held the fiber with surprising strength and were easy to use. The major problem was a fear that the fiber would be structurally damaged on the hard surface of the magnets. The fiber did not slip pulling on it with a small force, but did with a larger force.

1. Clamp: As with the magnets the structural integrity of the fiber while being clamped came into question.

1. 3M Tape: The sticky tape was easy to work with ad seemed to hold the fiber securely, but it made the fiber difficult to see and did not allow for precision alignment.

1. Elmer’s Glue: The Elmer’s glue was quick and easy to use, but the fiber could be pulled out easily as well (if you could find it).

1. JB Weld: The JB weld performed high in all the categories –especially the most important two. Its only drawbacks are that it takes longest to set and it is a little harder to use. So far it does not seem to cause any fiber damage but, due to the harsh nature of epoxy, the chemical integrity after applying JB to the fiber needs to be tested.

1. Hot Glue: The hot glue is handy, but not as strong as JB weld. It also makes the fibers extremely difficult to see because strands of glue that resemble the fine fibers often dangle off the glue area

1. Super Glue: Super glue damages the chemical makeup of the fibers.

1. Scotch Tape: The scotch tape is cheap and easy to use, but makes the fiber hard to see and does not hold it securely.

Table 1 shows that the best solution is to use the JB weld. Its final score was 90.5 out of a possible 117.5. Its high strength made it stand out among the other solutions because it was the only method that did not allow the fiber to slip (the fiber broke first). The next closest score was 80.5, which came from the 3M sticky tape. Based on this evidence, the team plans to use the JB weld in the final design to adhere the fiber to the attachment device. If a serious problem arises that prevents the use of the JB Weld, the 3M sticky tape and/or other untested adhesives will be considered as design alternatives.

Attachment device

The decision of which device to attach the fiber came down to the window and the precision rods as these options were easily integrated with the chosen adhesive. The advantages of the window are its inexpensive construction and ease of use. However it does have disadvantages in that this method would be limited to one use. The rod has the advantage of being machined to have better precision than the cardboard, ensuring the alignment, and it can combine easily with other systems because rods are a common machine part. The disadvantages of the rod are that it will cost more, require more design, and require high-tech precision CNC (Computer Numerical Control) machining.