1 INTRODUCTION The Department of Material Science and Engineering at the University of Toronto recently adopted a new set of 32

of stress-strain apparatus from PASCO. It is a hand-cranked, tabletop tensile machine capable of basic mechanical

analysis on tensile coupons. Each unit of the stress-strain apparatus costs approximately $1500, totaling to $48 000

for the entire acquisition [1]. The machine itself is currently used by students enrolled in MSE101 (560 students

working over two semesters) and APS104 (480 students working over one semester) as an experimental exercise.

1.1 BACKGROUND

A typical stress-strain curve obtained through tensile testing is illustrated below in Figure 1. The modulus of

elasticity (E), read directly from the linear region in the initial section of the curve, governs the elastic behaviour of

the material through Equation 1. To assist testing at high stress values of metal samples, tensile coupons typically

have a small cross-sectional area in the central gage section to reduce the necessary applied force, as seen in

Figure 2.

EQUATION 1 - CALCULATION OF MODULUS OF ELASTICITY

FIGURE 1 - TYPICAL STRESS-STRAIN CURVE OF COMMON METAL MATERIALS [3]

𝐸 𝑀𝑃𝑎 =𝑆𝑡𝑟𝑒𝑠𝑠

𝑆𝑡𝑟𝑎𝑖𝑛 (𝑖𝑛 𝑡ℎ𝑒 𝑒𝑙𝑎𝑠𝑡𝑖𝑐 𝑑𝑒𝑓𝑜𝑟𝑚𝑎𝑡𝑖𝑜𝑛 𝑟𝑒𝑔𝑖𝑜𝑛)

FIGURE 2 - ASTM E345 STANDARD FOR METAL FOIL TENSILE COUPON DIMENSION [2]

The applications for a tabletop provide first year students with an introduction of material characterization

techniques and tensile properties of metals and plastics. Through accurately demonstrating the correlation

between theoretical and actual values, the course instructor can highlight metal treatment effects on metal

characteristics.

1.2 PROBLEM STATEMENT

There are several problems factoring against the usability of the stress-strain apparatus from PASCO, acquired by

the Department of Material Science and Engineering. The major product issues are summarized into t elements:

The results of the stress-strain apparatus do not properly reflect the theoretical values provided by

PASCO, nor do they show consistency across trials of the same material

The annual cost of operating the stress-strain apparatus is heavily impacted by the proprietary design of

the samples

1.3 DESIGN OBJECTIVES

The ultimate goal for our capstone design project is:

To increase the usability and instructional value of tensile property lab experiment in the University of Toronto

undergraduate curriculum.

Our design attempts to address this goal by:

Increasing the accuracy and consistency of PASCO® stress-strain apparatus

Decreasing the annual recurring cost of operating the tensile testing experiment

1.4 STAKEHOLDER PROFILES

The stakeholders of the design projects involve all parties that may be affected by the project, both directly and

indirectly:

1.4.1 ESC471 DESIGN TEAM – TEAM DE The design team of the Capstone course is subjected to the requirements and the constraints set by other

stakeholders. The team is responsible of taking these requirements and constraints, and drafting, prototyping and

creating a feasible solution. The team needs to be able to balance this as well as other concurrent courses through

proper prioritization, in order to produce satisfying results in a timely manner.

1.4.2 ESC471 COURSE INSTRUCTORS The Capstone course, ESC471, is the motivator for the design group to look into the existing problems associated

with undergraduate labs. The assessment of the project in addressing the problem is done by both client, as well as

the course instructors. The legitimacy and quality of the design solution is based on the discretion of the course

instructor, Professor Nogami, and course teaching assistant, Sadakat. Through the course of the design, we will

also need to follow the guidance and the mentorship of the course instructors.

1.4.3 MSE101 AND APS104 COURSE INSTRUCTORS Professor Ramsay is the course instructor for MSE101, and as such, is one of the major clients to our design

solution proposal. Professor Mirkovic, Professor Nogami and Professor Kherani are the course instructor for

APS104, and also important clients of our design solution proposal. The proposed design solution aims to be

adopted into each of these courses that utilize the tensile testing machine.

1.4.4 MSE101 AND APS104 TEACHING ASSISTANTS The teaching assistants will be supervising the students in executing the lab procedures, and any changes in the

experiment should be sufficiently documented to provide training for each semester.

1.4.5 MSE101 AND APS104 STUDENTS The student of MSE101 will be the end users who will be executing the lab procedures. The final design solution

must be an appropriate application of the stress-strain machines for first year students to become familiarized

with physical sample characterization and metal and plastic stress-strain characteristics. The experimental

procedures must be safe for them to handle without causing personal harm.

1.4.6 LAB TECHNICIAN Dr. Grozea is the lab technician responsible for the overall maintenance of the lab equipment and its operations.

Therefore, any design changes to the lab would have to undergo feasibility and cost evaluations under his

guidance. Maintenance of laboratory equipment used for the experiment, including the tensile testing machines

themselves, should be outlined in the design documentation to approximate the time and effort of maintenance

by someone of his capacity.

2 PROBLEM DESCRIPTIONS

2.1 EXPERIMENTAL INACCURACY

Experimental data can suffer from errors and uncertainties, and first year experiments often experience higher

error margins due to the inexperience of students operating experiments, as well as an overall reflection of the

quality of the apparatus. However, the degree of how closely the result matches the known literature value is

important in determining the credibility of the associated method of testing. Hence, if the tool is producing highly

inaccurate and inconsistent results, its usage as an instruction tool proves challenging for course instructors.

FIGURE 3 - THE MECHANICAL PROPERTY OF THE CURRENT SAMPLE COUPONS PROVIDED BY PASCO® [4]

The students utilizing the tabletop tensile machine work on four types of metals and 4 types of plastics, listed in

Figure 3, above. The plastic samples were tested with accurate results; however, the metal sample characteristics

did not match with the mechanical characteristics provided by PASCO. The results obtained from our client,

Professor Ramsay, are shown in Figure 3 below. They demonstrate that only the dominant features of each metal

coupon are observable in the results. Those features are summarized in Table 1.

Sample Distinguishable Features

Cold-rolled steel Negligible elongation the plastic deformation region

High yield strength Aluminum Little elongation segment in the plastic deformation region

Low yield strength Annealed Steel Significant elongation segment in the plastic deformation region

Characteristic necking behaviour in the stress-strain curve Brass Moderate elongation segment in the plastic deformation region

Moderate yield strength TABLE 1 - DISTINGUISHABLE FEATURES OF THE TESTED METAL COUPONS, THIS IS IN AGREEMENT WITH THE THEORETICAL VALUES

FIGURE 4 - EXPERIMENTAL STRESS-STRAIN RESULTS FROM THE CLIENT, PROFESSOR RAMSAY FOR ALL FOUR VARIETIES OF METAL COUPON

WITH A THICKNESS OF 0.003 INCH. (TOP LEFT) COLD-ROLLED STEEL SHEET. (TOP RIGHT) ALUMINUM FOIL. (BOTTOM LEFT) ANNEALED STEEL.

(BOTTOM RIGHT) BRASS [5]

On the other hand, the numerical values of the data collected greatly differ. The tabulated values of the provided

sample results are summarized in Table 2. The percent error has been calculated by utilizing Equation 2.

Cold-rolled steel Annealed Steel Aluminum Brass

Experimental E (Mpa) 146,667.00 24,000.00 55,000.00 60,000.00

Theoretical E (Mpa) 200,000.00 200,000.00 69,000.00 117,000.00

% Error 26.67% 88.00% 20.29% 48.72% TABLE 2 - EXPERIMENTAL CALCULATION OF THE RESULTS OBTAINED BY PROFESSOR RAMSAY

𝐸𝑟𝑟𝑜𝑟 |𝐸 𝐸 |

𝐸

ℎ𝑒𝑟𝑒 𝐸 𝑖𝑠 𝑡ℎ𝑒 𝑀𝑜𝑑 𝑙 𝑠 𝑜𝑓 𝐸𝑙𝑎𝑠𝑡𝑖𝑐𝑖𝑡

EQUATION 2 – CALCULATION OF PERCENT ERROR

The results of experiments are very much dependent on the conditions and parameters used in the experiment. As

Professor Ramsay’s results were obtained under unknown condition, the design team also performed the

experiment multiple times to verify the calculated experimental inaccuracies. The results of 12 runs the

experiments are summarized in Table 3, below. The extrapolation of the raw data is provided in Appendix 5.1. The

experiments are performed in closely monitored environment, where the team member responsible for executing

the procedure, making the measurements, and analyzing the data remained constant throughout the multiple trial

processes to reduce variability.

Modulus of Elasticity

Sample Run Experimental Theoretical % Error

Aluminum 1 84,073.36 69,000.00 21.85%

Aluminum 2 55,439.37 69,000.00 19.65%

Aluminum 3 86,674.81 69,000.00 25.62%

Aluminum 4 88,136.40 69,000.00 27.73%

Brass 1 204,427.40 117,000.00 74.72%

Brass 2 219,728.97 117,000.00 87.80%

Annealed Steel 1 460,067.00 200,000.00 130.03%

Annealed Steel 2 521,461.74 200,000.00 160.73%

Annealed Steel 3 685,149.35 200,000.00 242.57%

Annealed Steel 4 490,231.53 200,000.00 145.12%

Cold Rolled Steel 1 109,457.45 200,000.00 45.27%

Cold Rolled Steel 2 135,935.00 200,000.00 32.03% TABLE 3 - EXPERIMENTAL RESULTS OF METAL COUPONS PROVIDED BY PASCO VS THEORETICAL RESULTS

There are some notable similarities between the design team’s experimental data and the data provided by

Professor Ramsay.

Discrepancies exist for all metal samples from the provided PASCO characteristics

The degree of inaccuracy is dependent on the material of the coupon

Within both sets of data, the aluminum samples exhibited the most consistent values, followed by cold-

rolled steel and brass. Annealed steel suffers from the most error

By observing the experimental, the team has categorized the significant errors between concluded two major

categories of error outlined below. These sources, together, are believed to contribute to the overall experimental

inaccuracies of the tested results

Random error: Innate sample defects, limitation in equipment resolution and measurement uncertainties

Systematic error: Design fault in the original coupon-clamp interface, the stress-strain apparatus, as well

as the experimental procedures

2.1.1 RANDOM ERRORS Even within an industrialized coupon-punch process, not all samples are created equal. Point defects and localized

stress points caused by the coupon punch process would likely cause minor deviations of sample properties within

a box of supplied samples. Unfortunately, without the full knowledge of the coupon making process, it becomes

difficult to calibrate the data collection process to account for these defects, and it must be treated as random

defects for the purpose of the tensile testing experiment. Additionally, the limited sample dimensions make

precise measurements difficult, as the equipment uncertainties are often on the same order of magnitude as the

data collected.

The PASCO® rotational motion sensor has a linear resolution of 0.02 mm, the force sensor has a resolution of 0.03

N [6] and the digital caliper has a resolution of 0.01 mm. Normally, these precisions are sufficient for experimental

purpose. The coupons used in the lab, in comparison however, are only 0.0762 mm in thickness. Measurements of

using digital caliper, at its best, will have a reading of 0.08 mm, corresponding to a 5% uncertainty on just one of

the many different data values collected. Figure 5, below, provides the experimentally calculated dimensions of all

12 trials performed initially. The average cross-sectional area measured of the tested 12 runs is 0.2951 mm with

standard deviation of 0.019 mm, while the average nominal length of the reduced-width section of the coupons

measured at 79.9213 mm, with standard deviation of 0.115 mm.

Taking the consideration of these errors, the design team acknowledges the limitation of improvements to the

experimental accuracy within 10% of the theoretical value for the modulus of elasticity of all samples.

FIGURE 5 - EXPERIMENTAL DATA OF CROSS-SECTIONAL AREA (TOP) AND NOMINAL LENGTH (BOTTOM) FOR THE 12 TESTED NORMAL METAL

COUPONS. FORMAT FOR THE LABELLED: MATERIAL-RUN#. AL - ALUMINUM. AS - ANNEALED STEEL. BR - BRASS. CRS - COLD-ROLLED STEEL.

0.250

0.260

0.270

0.280

0.290

0.300

0.310

0.320

0.330

AL- 1 AL- 2 AL-3 AL-4 AS-1 AS-2 AS-3 AS-4 BR-1 BR-2 CRS-1

Cro

ss-s

ecti

on

al A

rea

(mm

)

Cross Sectional Area Variability of Tested Samples

Experimental Results Theoretical Value by PASCO

79.000

79.200

79.400

79.600

79.800

80.000

80.200

80.400

80.600

80.800

81.000

AL- 1 AL- 2 AL-3 AL-4 AS-1 AS-2 AS-3 AS-4 BR-1 BR-2 CRS-1 CRS-2

No

min

al L

engt

h (

mm

)

Nominal Length Variability of Tested Samples Experimental Results Theoretical Value by PASCO

2.1.2 EQUIPMENT IMPACT

2.1.2.1 CLAMP

During testing, the team discovered a high amount of internal stress within the coupon samples as the the clamp

and the apparatus setup tightened. In order to secure the smooth metal surface when stretched, the clamp must

be able to provide enough friction to prevent slipping. The current design of the clamp is provided in Figure 5. The

securing mechanism is largely dependent on the ridge on the clamp top. Furthermore, before running the

experiment, the nut cannot be secured by hand. A wretch must be used it to tighten.

FIGURE 6 - COUPON CLAMP THAT IS CURRENTLY USED ON STAGE TO HOLD THE SAMPLE

The effects of the clamp top are most noticeable in spent coupons: each coupon has a crease line along the clamp

teeth after experimentation. As seen in Figure 7 below, the spring loaded under the clamp top is exerting a

bending force on the metal sample around the clamp teeth.

FIGURE 7 - THE SAMPLE AFTER STRESS-STRAIN EXPERIMENT. ALL SAMPLES SHOWN HAS A CREASE ON CLAMP SECTION OF THE COUPON

(TOP LEFT). DURING THE TEST, THE RIDGE CAUSES THE FLANGES TO BENT UPWARDS (TOP RIGHT), CAUSING THE DISTINCTIVE UPLIFT

VERTICALLY OF THE ENDING PRODUCT (BOTTOM)

2.1.2.2 HAND CRANK AND DISTRIBUTION OF STRESS

In order to verify whether an apparatus is usable for a specific lab, it is important to realize its range of operation.

The general setup of the PASCO® Stress/Strain Apparatus is shown in Figure 7. The Apparatus utilizes a tabletop

hand crank to generate force, and digital sensors to transmit electronic data of force exerted, and strain observed

to laptops equipped with DataStudio.

To observe for any uneven stress behaviours occurring with the sample while searching for a reason as to why the

coupon do not always break in the middle, an experiment is carried out to study the strain distribution associated

with each segment of the coupon along its length, as the forces are being applied. Markings were made on the

sample with 10 mm spacing. Eight segments were created long the nominal length of 80 mm. A “T” shaped

marking is created on each end to study the effect of the clamp. The setup is illustrated in figure 8.

The distribution of stress is tested on two aluminum samples and two annealed steel samples. This is summarized

in table 4. They correspond to aluminum and annealed steel; run 3 & 4, in table 3. Several findings can be noted:

The stress distribution is not even throughout the sample, even though the cross sectional area should be

consistent throughout.

More compressions are observed on the two end rather than tensions

Breakage is more likely to occur towards the force sensor side. The force sensor side is connected has a

movable lever arm attached to it. Hence, it is more likely to cause additional stress on one side.

FIGURE 8 – THE SETUP OF THE PASCO® STRESS/STRAIN APPARATUS [2]

FIGURE 9 - SETUP TO ALLOW UNEVEN STRESS DISTRIBUTION

TABLE 4 - STRESS DISTRIBUTION ALONG THE LENGTH OF THE SAMPLE COUPON DURING EXPERIMENT. RED CELLS INDICATE THE BREAKAGE

OCCURRED THERE.

2.1.2.3 PROCEDURAL FLEXIBILITY

The rate at which the tension test is performed can have a significant effect on the result tensile speed. Studies

have shown that plastics, polymers, and steels are very sensitive to the testing rate, but aluminum alloy are less

sensitive [5]. This potentially explains why the aluminum coupons have very similar results between Professor

Ramsay and the design team, yet the annealed steel coupons are very dissimilar.

Speed-sensitive materials usually will exhibit a higher tensile stress and lower elongation at faster speed.

The lab procedure of tensile testing lab did not provide an instruction to allow consistent spinning speed, and thus,

the students in a classroom may potentially experience very different results depending on their testing speed.

Figure 10 provides the procedure section of the lab from MSE101.

FIGURE 10 - PROCEDURE FROM THE 2012 MSE 101 STRESS STRAIN LAB AS PROVIDED BY PROFESSOR RAMSAY [6]

seg 1 seg 2 seg 1 seg 2 seg 3 seg 4 seg 5 seg 6 seg 7 seg 8 seg 1 seg 2

Original Length mm 10.00 5.00 10.00 10.00 10.00 10.00 10.00 10.00 10.00 10.00 5.00 10.00

Sample Run

Aluminum 3 9.81 5.11 10.35 10.10 10.24 10.29 10.28 10.07 10.07 4.53 10.35

Aluminum 4 9.49 4.76 10.33 10.05 10.22 10.24 10.25 10.03 10.04 4.52 9.81

Annealed Steel 3 9.97 5.13 12.36 13.92 13.67 13.36 13.22 12.57 11.14 5.26 10.06

Annealed Steel 4 9.75 4.62 11.35 13.21 12.59 12.08 12.08 11.92 11.96 4.62 9.54

Length of each segment after test

Visual

(See Figure 8)

Motion

Sensor Side

Force Sensor

EndNominal Length

T. . . . . . . . . T

Procedure 1. Move the lever arm so that it is touching the force sensor (See Figure 1) 2. Loosen the clips on the apparatus and insert the sample 3. Ensure that the sample is not under stress in its rest position before you tighten the clips 4. Turn the crank counter-clockwise enough so that lever arm can be pushed against the starting peg, away from the force sensor 5. Tare the force sensor and press “Start” before turning the crank clockwise to begin

Figure 1

2.1.3 CONSTRAINS & REQUIREMENT The force sensor is one of the key limiting factors in this process. For us to increase sample accuracy, it is necessary

for the sample to be able to detect by the range of the force sensor. The force sensor has a total detection range of

100 N (from +50N to 50N) and is able to collect up to 1000 samples per second. The apparatus itself has a 5x step-

up rate, which brings the workable range to 250 N.

Work within the workable range of the equipment and apparatus. The design team should try to minimize the

modification to the machine itself. This is because the then the design must be carried over to all 32 machines, and

consistent construction may not be feasible. Also, they are expensive equipment and potential damages during

experimental setup should be avoided

In the redesigning and improving the result, the team must insure that the lab only improves the result, but should

still cover the lecture material as taught in MSE101. It should focus on improving the results associated with

Modulus of elasticity, and other mechanical behaviour expression discussed by the MSE 101 ourse.

The improvement should be safe for the students to handle. For any mechanical constructions, the roughness and

the potential hazard should be considered.

Ultimately, the design team should try pushing both the precision and the accuracy of the student results. The

results should be able to repeatable.

2.2 LAB PROCEDURAL COST

The samples that each stress-strain apparatus takes are extremely limited to the constraints of the various sensors

on the apparatus. The apparatus is only able to measure coupons made from metal foil material (with thickness

under 0.006” [2]) to accommodate the limited operating range of the equipment. The shape of the coupon is

further limited in dimensions to the clamp fittings on the apparatus. As a result of accepting only non-standardized

coupon samples, annual recurring charges are paid to PASCO® for purchases of their tensile testing refills. This cost

quickly accumulates for large classes over the years of operating the experiment, as the tensile analysis is entirely

destructive on the coupon samples.

2.2.1 RECURRING CHARGES There are significant recurring costs that are incurred by consumable materials every time this lab experiment is

hosted by either the MSE101 or APS104 course. These costs come from the usage of metal and plastic coupons

required to perform tensile stress/strain testing and are significant due to the number of students performing the

experiments. This section will investigate the source of these costs in detail and provide constraints for an

appropriate solution.

Currently, there are two first year engineering courses which make use of the PASCO machine for a tensile

stress/strain lab experiment:

MSE101 (Fall and Winter): 280 students in groups of 2 = 140 groups per semester

APS104 (Winter only): 480 students in groups of 4 = 120 groups

Each group runs one instance of the experiment. Each instance requires the following materials:

6x metal coupons2

4x plastic coupons

Total samples consumed during one academic school year (fall and winter semesters):

140 groups per semester*2 semesters+120 groups=400 groups

2400 metal coupons consumed

1600 plastic coupons consumed

All coupons are currently supplied directly by PASCO, the supplier of the apparatus. Replacement coupons are

currently available in sets of 70 coupons consisting of 50 metal coupons and 20 plastic coupons. Additional

coupons can also be purchased separately as sets of 50 metal coupons or sets of 20 plastic coupons. the prices are

outlined below as quoted from the PASCO catalogue.

Cost of 1x set of 50 metal coupons and 20 plastic coupons = $154

Cost of 1x set of 50 metal coupons = $108

Cost of 1x set of 20 plastic coupons = $553

The consumption requirement of the courses can be fulfilled if the 70 coupon sets are purchased and

supplemented by additional 20 coupon plastic sets. The total annual cost is outlined below.

2400 metal coupons/50 metal coupons per set=48 sets of 70 metal & plastic coupons

1600 plastic coupons-48 sets*20 plastic coupons per set=640 plastic coupons remaining

640 plastic coupons remaining/20 plastic coupons per set=32 sets of 20 plastic coupons

48 sets of 70*$154 per set=$7392

32 sets of 20*$55=$1760

$7392+$1760=$9152 Total Cost

As shown, in order to fulfill the requirements of the lab experiment for one academic year, 48 sets of 70 metal and

plastic coupons and 32 sets of additional plastic coupons must be purchased. This cost totals $9152 per academic

year. This is a significant cost which can be reduced by producing the coupons from raw materials instead of

purchasing coupons directly from the vendor.

2.2.2 CONSTRAINTS

The solution to the lab procedural cost problem must fall under the follow financial and scientific constraints:

While there may be significant costs required as an initial investment, the annual recurring costs must be

significantly less than current costs such that the initial investment can be recovered within 7 years time

which is equal to the depreciation period/lifespan of the PASCO machines..

The solution must be able to provide coupons at the same quantity that is currently available by

purchasing from the vendor.

The coupons produced must be able to yield scientific results of the same quality/consistency or better of

current coupons.

2 [Data as provided by Professor Scott Ramsay and Professor Jun Nogami]

3 [http://www.pascocanada.com/catalogs/PASCO_Canada_Pricelist_Jan_2012.pdf]

The solution must be able to provide coupons at any time, without restriction.

3 DESIGN SOLUTION

3.1 PROCEDURE The major component of procedural refinement will be focused on the creating a standard for testing speed. Effort

was also put towards creating a more standardized lab so the lab can be performed consistently.

3.1.1 POTENTIAL RESOLUTIONS The American Society for Testing and Materials (ASTM) created many standards for different material testing

method. One of the standards provided were the testing standard for metallic foils. There are two proposed

methods of determining the elastic region [ASTM standard].

The testing speed as a function of stress application. The speed should be controlled at 12MPa/s or

1.2MPa/s

The testing speed as a function of strain application. The strain rate should be 0.002 to 0.010 in/in per

minute until above yield

The majority of the students who will be using the lab will be first year undergraduate students. It is very hard to

control the rate of force application. The force will be dependent on the individual. Furthermore, for materials

with higher tensile strength, individuals will also more likely to apply more force.

In contrast, the strain rate is relatively easy to control. The elongation is measured in terms of angular motion.

Angular motion can be easily converted to turns per seconds. The rate of turning is fairly easy to control. Hence,

using strain to benchmark will be adopted.

3.1.2 RATE OF STRAIN APPLICATION The rate of the strain application is suggested to range from 0.002 to 0.01 for metallic foils. The resolution of the

angular motion sensor is 0.002, equivalent to the lower end of the suggested range. However, even with a

standard, the possible variation in student performance should still be considered. Therefore, using the lower end

value will create noticeable effect from slower turning speed for some students. Similar logics also apply to the

upper range of the recommended value. To accommodate the largest range of possible experimental deviations,

the strain of 0.006 in/in – minute will be used.

The nominal length of the coupons must be around 80 mm to fit into the two clamps of the apparatus. This is

equivalent to an elastic elongation of 0.48 mm/min. For each revolution, the linear displacement of the coupon

clamp is 1 mm/ revolution. However, this speed is impractical for student lab sessions.

Due to the limitation of materials, thicker brass of (0.005”) was used. The measured results were summarized in

table. The improvement based on the decreasing speed can be observed. The raw results are provided in Appendix

5.2.

Modulus of Elasticity Speed

Sample Run Experimental Theoretical % Error sec/revolution

Brass - Thick 1 186,943.16 117,000 59.78% 2

Brass - Thick 2 138,606.39 117,000 18.47% 4

Brass 3 106,845.76 117,000 8.68% 8

Brass 4 177,709.57 117,000 51.89% 1 TABLE 5 - SPEED SAMPLE TEST OF 4 BRASS COUPONS

In the duration of the lab session, student group has multiple segment of the lab they must complete. The

allocated time for using the apparatus varies between 25 – 45 min4. With 10 samples (6 metals and 4 plastic) to

complete, as well as the setup time, the student may only have 2-3 minute spent on each coupon. If 2 min per

coupon can be allocated, then the speed of the following are recommended:

Aluminum: 3 sec /revolution

Brass: 6 sec/revolution

Annealed Steel : 4 sec/revolution

Cold-rolled Steel: 10 sec/revolution

This is fairly convenient and feasible due to the fact that DataStudio came with an embedded stop watch. This

selection from the was based on data calculated in Appendix B (Section 5.2) as well as several other considerations

including

The time spent on each revolution cannot be too long – over 10 sec/rev. The student will not be able

evenly distribute the force properly all the time beyond 10 sec/revolution.

Material difference – Aluminum are less sensitive than steel, therefore, the speed reach the time per

revolution as calculated to be slowed for such experiment.

3.1.3 ADDITIONAL REVISION TO LAB PROTOCOL In addition to adding the information regarding the speed of the test, additional protocols will be add for the order

of screwing, as well as consideration during calibration. The lever arm in particular, often cause angular shift in the

sample and should be held steel when calibrating the data.

3.2 SHAPE In order to address the problem of the apparatus, the team has decided to change the shape of the coupon in

order to compensate for the flaws that exist in the apparatus itself.

Modulus of Elasticity

Sample Run Shape Experimental Theoretical % Error

Aluminum 1 Rectangular 66,925.47 69,000.00 3.01%

Aluminum 2 Rectangular 143,732.85 69,000.00 108.31%

4 Estimation

Modulus of Elasticity

Sample Run Shape Experimental Theoretical % Error

Aluminum 1 Tapered 261,630.86 69,000.00 279.18%

Aluminum 2 Tapered 149,238.59 69,000.00 116.29%

The best result is obtained by decreasing the gauge length. Experiment is conducted on the brass sample using the

following parameters.

A B C Modulus of Elasticity

Sample mm mm mm Experimental Theoretical % Error

Widened Gauge Sample @ 1 sec/rev - Run 1 18 35 8 73,037.00 117,000.00 37.58%

Widened Gauge Sample @ 1 sec/rev - Run 2 48 25 6 108,186.00 117,000.00 7.53%

3.3 PUNCH & DIE BLANKING PRESS

3.3.1 OVERVIEW To address the issue of procedural cost, as well as making the shape solution feasible, the proposed solution is to

design and fabricate a blanking press which will be able to produce coupons of a predetermined shape from raw

sheet metal or shim stock. The control over the coupon shape will provide a solution to the experimental

inaccuracies previously outlined and the use of raw materials will address the issue of recurring material cost.

A blanking press consists of a die, punch and counterpunch attached to a press machine which punches out shapes

from raw sheet material. The counterpunch acts as a counter-force to minimize edge stresses during punching; it

also provides a platform for ejecting the punched material so it can be immediately removed from the machine

and stored. This particular type of punch press is only different for a standard punch (pierce) press in that the part

which is ultimately used is the punched shape rather than the raw sheet from which the shape is removed. The

processes are otherwise identical.

The coupons that will be produced will be roughly 0.003” in thickness, consistent with the current coupons

available from PASCO. A preliminary search for vendors with raw materials at the desired thickness yielded

McMaster-Carr (MC) as a possible candidate. The cost analysis of purchasing raw materials from MC is provided in

the following section.

3.3.2 COST ANALYSIS

3.3.2.1 PLASTIC COUPON COST

Since this press solution only deals with metal coupons, it is assumed that plastic coupons will still be periodically

purchased from PASCO. This cost is as follows:

1600 plastic coupons per year/20 coupons per set=80 sets per year

80 set per year*$55 per set=$4400 per academic year

$9152 total cost-$4400 plastic coupon cost=$4752 remaining potential savings

This leaves $4752 of annual cost that can be saved before taking into account the cost of raw materials from MC

and the cost of labour.

3.3.2.2 LABOUR COST

The operation of the proposed press machine is manual which means that the cost of labour must be accounted

for. As such, it is imperative to maximize the efficiency of the punch by producing multiple coupons simultaneously

to minimize labour time and cost.

The University of Toronto Work Study program provides employees at $10.25 per hour plus 4% vacation pay5.

Assuming that the labour can be provided by the University of Toronto Work Study program, and that one cycle of

operation for the machine is 8 seconds6 the labour costs can be determined depending on how many coupons are

produced per cycle of operation. If 1 coupon is produced per cycle, the total time for 2400 coupons is 19200

seconds. This equates to a total of 5 hours and 20 minutes assuming consistent and continuous working time. This

time can be rounded up to 6 hours to account for breaks and various stoppages; the cost of labour is $63.96 at a

pay rate of $10.25 per hour and 4% vacation pay.

3.3.2.3 RAW MATERIAL COST

The punching process, while efficient, will always yield scrap pieces that are unusable which is determined by the

punching pattern used on the raw material. By maximizing useful space and minimizing scrap, this cost can be

mitigated.

The process of punching coupons will apply stresses onto the raw material and induce strain in the surrounding

area; in order to minimize waste material while maintaining coupon quality and uniformity, a minimum distance

between punched coupons must be set.

Given that the coupons are 15 mm in width and that it is expected there is no induced strain from the punch

process when these coupons are produced, a reasonable gap between coupons can set at 15 mm to ensure defects

are isolated and localized to each coupon. Consequently, it can be assumed that each coupon punched will take up

the following area on the raw material:

5 http://www.careers.utoronto.ca/jobsearch/workstudy.aspx

6 Arbitrary metric

Calculated area: (15mm+15mm)*(100mm+15mm) = 3450 mm2 OR 5.348 in

2 per coupon

A vendor is required for obtaining all raw materials. Currently McMaster-Carr is the most ideal candidate as they’re

able to provide all materials at the thickness required. Listed below are each material and their respective costs

from McMaster-Carr at a given size as well as the number of samples producible per unit of raw material given the

space efficiency specified above.

Low Carbon Steel Shim Stock (9500K37)7

[0.003” thick, 12” wide, 120” long] - Area of 1440 in2

Cost: $32.24 per sheet.

Each sheet is able to produce roughly 260 samples.

Good for: Cold Rolled Steel, Annealed Steel

FIGURE 11 - AREA USED BY ONE COUPON ON RAW SHEET MATERIAL, USEFUL + WASTE MATERIAL, IN (MM)

Aluminum Shim Stock (9536K32)8

[0.003” thick, 12” wide, 24” long] - Area of 288 in2

Cost is $7.65 per sheet. Each sheet is able to produce roughly 53 samples. Good for: Aluminum

Brass Shim Stock (9299K3)9

[0.003” thick, 12” wide, 120” long] - Area of 1440 in2

Cost is $37.08 per sheet. Each sheet is able to produce roughly 260 samples. Good for: Brass #1

Brass Shim Stock (9299K5)10

7 http://www.mcmaster.com/#steel-shim-stock

8 http://www.mcmaster.com/#aluminum-shim-stock

9 http://www.mcmaster.com/#shim-stock/

[0.005” thick, 12” wide, 120” long] - Area of 1440 in2

Cost is $53.03 per sheet. Each sheet is able to produce roughly 260 samples. Good for: Brass #2

Since a total of 2400 coupons are required, they can be divided equally among all 5 different materials in the

following manner:

960 coupons of cold rolled steel (480 annealed, 480 cold rolled)

480 coupons of aluminum 480 coupons of brass #1 480 coupons of brass #2 960/260 = 4 sheets = $128.96 480/53 = 10 sheets = $76.50 480/260 = 2 sheets = $74.16 480/260 = 2 sheets = $106.06

Total cost is $385.68 in recurring costs of raw material from MC. This price assumes maximum space efficiency and

does not include tax or shipping costs. The maximum space efficiency value is an ideal value, if it holds true then

the total amount of money saved per year in recurring costs will be:

$4752 cost-$63.96 labour-$385.68 raw materials=$4302.36 of savings per year

To account for less than ideal space usage, it can be assumed that the space efficiency is cut in half, thereby

doubling the cost of raw materials. Number In this case the amount of money saved per year will be:

$4752 cost-$63.96 labour-$771.36 raw materials=$3916.68 of savings per year

3.3.3 PRESS FEASIBILITY In blanking operations, there are several important factors to take into account. As illustrated in Figure 11, the

shearing force is exceptionally crucial in the operation.

Disregard the factors such as friction, the force required for shearing can be modelled by the equation (Groover,

2007):

𝑆 𝑡

F = Shearing Force t = sheet thickness L = Length of the cutting S = Shear strength of the metal

For our purposes, the shear strength of the metal can be approximated by (Groover, 2007):

10

http://www.mcmaster.com/#shim-stock/

𝑆 𝑙𝑡𝑖𝑚𝑎𝑡𝑒 𝑒𝑛𝑠𝑖𝑙𝑒 𝑆𝑡𝑟𝑒𝑛𝑔𝑡ℎ

Referring back to the dimensions of the metal coupon as specified in Figure 12, we can readily calculate this

number for Cold-rolled Steel, the material of the highest tensile strength in the samples provided by PASCO®.

FIGURE 12 - MAIN FORCE COMPONENTS IN A FINE BLANKING PRESS

Since the team is unable to specify the type of cold-rolled steel used by PASCO®, the team proceeded with the

calculation for 1144 (Stressproff-equivalent) Steel. This specific alloy has yield strength of 100,000 psi (higher than

the quoted yield strength of PASCO® cold-rolled steel of 90,000 psi). Therefore the force calculated for 1144 alloy

will surely produce all the metal samples provided by PASCO®.

The ultimate tensile strength of the 1144 alloy is 115,000 psi (approx. 793 MPa) (Eagle National Steel, 2009). The

parameter of the sample is approximately 0.25 m. Thickness of the sample is 7.62*10-5

m (the current MSE101class

only uses the 0.003inch-thickness sample). Hence, the approximate force required to shear the metal sheets is:

Fine blanketing machine can easily exert up to a few hundreds tonnage in force in industrial applications. Machines

of smaller scale can easily supply the force we needed. A simple desktop arbor press can supply 1 ton of pressure

(Greasy Machine) (Michaelson's).

The difference between normal punch operations and blanking operations is that the punched-pieces in blanking

operation are the useful component and the surrounding are discard. This introduced precision requirements in

designing the die. Clearance shearing in die and punch set ranges from 4% - 8% of the sheet thickness. Considering

the thickness of the metal coupon, this precision is hard to be achieved without the assistance from local machine

shop.

FIGURE 13 - THE DIFFERENCE BETWEEN A PUNCHING PRESS AND A BLANKING PRESS

3.3.4 PRESS DETAILS

3.3.4.1 PUNCH

The punch will consist of two major components,

top plate

shaped punch

The top plate serves as the attachment point to the top portion of the press. This will be the moving component of

the press, forcing the punch down into the die. The shaped punch will be directly attached to the top plate on the

opposite of surface of the press attachment. See appendix [1]

3.3.4.2 DIE

The die will consist of three major components,

Base plate

Die

Counterpunch

The base plate serves as the platform for the die; it will rest on top of the press affixed to the base. The die will be

attached directly to the base plate; it will contain a negative of the coupon shape which will complement the

punch. Finally, sitting within the die and attached to the base plate will be the counterpunch. This component will

consist of a block in the same shape as the punch while resting on springs attached to the base plate. The counter-

punch will fit inside the die negative and serve as both a counter-force to the punch as well as an ejector for when

the punch is released.

3.3.4.3 PUNCH-DIE ALIGNMENT

It is necessary to align the top and bottom plates such that the punch will fit into the die when lowered onto it.

While considerations are still being made, there following strategy may be the most suitable.

It is possible to have guide rods protruding from the base plate that reach up to and through the top plate. Given

sufficient thickness of the top plate, all degrees of freedom other than the vertical should be sufficiently restricted

and the pieces should be well aligned.

3.3.4.4 PRESS

Ideally an existing press within the University should be used to save the additional expense of purchasing a press;

however, such resources are not available. As such, there is currently a few candidate presses available locally that

can be purchased, further investigation is required to determine which, if any, are suitable.

http://www.princessauto.com/pal/product/8382756/Presses/10-Ton-Hydraulic-Bench-Top-Press

http://www.princessauto.com/pal/product/8150930/Presses/12-Ton-Shop-Press

3.3.4.5 SHAPE CONSIDERATIONS

Since the top plate and the shaped punch are two separate sections, the shaped punch can be swapped out at any

time with a different shaped punch provided the attachment points are consistent. This allows future flexibility of

this system so that if a different shape coupon is needed in the future, a shaped punch can be fabricated and

attached to the top plate. The complementary die and counterpunch will also be required but should also be as

easily designed and fabricated.

3.3.5 POTENTIAL ISSUES & RESOLUTIONS If the tolerances for the guide rods and top plate are too strict, there may be too much friction to allow for

movement of the top plate and punch.

Lubrication will be required for the guide rods; ideally a solid state lubricant but various greases or Si lubricant

could be appropriate.

4 CONCLUSION The problem faced by the design team, as well as course instructors utilizing the stress-strain apparatus from

PASCO, can be summarized as high experimental inaccuracies in the values derived, and high procedural cost for

continued operation of the experiment at large volumes. Our approach to the limitations of the current

experiment is to first construct a sample punch machine, allowing course instructors to produce samples in house

for future iterations of the experiment. Not only will this solution resolve the cost concerns of operating the lab,

the in-house sample making process enables us to alter the sample shape of the coupons used. Along with

modifications to the existing laboratory procedures, we strive to address both the random errors of measurement

uncertainties for such small values, as well as material characteristic changes at small values.

5 APPENDIX

5.1 APPENDIX A – EXPERIMENTAL RESULTS WITH METAL COUPONS The following diagrams include the raw data as well as modulus of elasticity extraction using Data Studio Slope

utility.

5.2 APPENDIX B – RAW DATA RESULTS OF TESTING SPEED VARIATION

Recommended Time Spent

Theoretical Elongation

Nominal Length

Theoretical Elongation

Revolutions Required

Estimated Time per

Revolution

min % mm mm Rev. sec/rev.

Aluminum 0.5 6% 80 4.8 4.8 6.25

Brass 2 25% 80 20 20 6.00

Annealed Steel

2 44% 80 35.2 35.2 3.41

Cold Rolled Steel

3 0% 80 0 0 N/A

5.3 APPENDIX 3 – SHAPE VARIATIONS

6 WORKS CITED

[1] AYVA Educational Solutions Limited, "PASCO Canada Price List," Ayva, Oakville, 2012.

[2] "Metallic Materials Properties Development and Standardization".

[3] ASTM International, "ASTM Standard E345," ASTM International, West Conshohocken, 2009.

[4] PASCO Scientific, "Stress-Strain Apparatus Manual," PASCO, Roseville.

[5] S. Ramsay, Stress and Strain Lab, University of Toronto, 2012.

[6] PASCO Scientific, "Rotary Motion Sensor PS-2120 Manual," Roseville, 2005.

[7] M. P. Groover, Fundamentals of Modern Manufacturing, Third Edition, 2007.

[8] Eagle National Steel, "Technical Specification of Steel," Eagle National Steel,

http://www.eaglesteel.com/download/techdocs/Carbon_Steel_Grades.pdf, 2009.

[9] Greasy Machine, "Metal Stamping Presses," [Online]. Available: http://www.greasymachines.com/metal-

stamping-presses.asp. [Accessed 30 09 2012].

[10] Michaelson's, "Amazon," [Online]. Available: http://www.amazon.com/Arbor-Press-1-Ton/dp/B00077KLIW.

[Accessed 30 09 2012].