Design Tech HL Year 1 Assignments
2012-2013

Overview - In this assignment , you will explore several of the quantitative techniques engineers and designers use to make appropriate design decisions. For example, if a safety engineer knows that a new elevator design will have a total passenger and elevator car weight slightly less than 3,800 pounds, would it be appropriate to use an elevator cable with a 4,300 pound tensile strength? What would happen if two or three additional passengers squeeze into the elevator car? The results could be disastrous!

You will see that designers and engineers don't guess in order to find solutions to a problem. Instead, they most often use quantitative (mathematically based) techniques to arrive at a solution to a design problem. Now, that may sound overly rigid and suggest that designers and engineers would sacrifice aesthetics (qualitative elements) for performance. Well, in some situations, this might be the case. (Let's face it - when you ride in an elevator, your main concern is to be able to move between floors quickly and safely.) In most situations, design is a compromise between the quantitative (performance) and qualitative (aesthetic) characteristics of the product. (The elevator manufacturer wants to make your ride on the elevator a pleasant journey, and the aesthetics of the elevator's interior contribute to the pleasantness of the journey!)

The Concepts - The quantitative design elements that will be studied in this activity include:

    Mass, Density, and Specific Gravity - Click here to see how to calculate density and SG.

    Mechanical Stress (Tensile, Compressive, and Shear) - Click here to see how to calculate stress.

    Factor of Safety - Click here to see how to calculate factor of safety.

    Percent Elongation - Click here to see how to calculate percent elongation.

    Thermal Stress (Coefficient of Thermal Expansion) - Click here to see how to use the coefficient
    of thermal expansion to calculate a change in size resulting from a change in temperature.

    Center of Gravity - The center of gravity calculation may be highly complex. We will use the computational power
       built into our CAD program to determine the center of gravity.
       Click here to learn more about the center of gravity.

Procedures:
1. Determine the desired quantity for each of the following problems (show all of your work for full credit)


Need a calculator? Click on the calculator to access the calculator tool.   

    a. A 5.5" square wood column (vertically positioned and referred to as a 6 x 6) is used
       in a basement to carry the load from the floor and partitions above it. Given that the
       load on the column is 73,500 pounds, what is the unit stress (in PSI) that the column
      demonstrates?

    b. Assuming that the maximum or failure stress for the material used in the column above is
      3,200 PSI, what factor of safety was used in this application?

    c. If the wood column were replaced with a hollow steel column that has a 3.5" O.D.
      (outside diameter) and a 3" inside diameter (I.D.), what unit stress (in PSI) would be
      present in the steel column?

    d. If the designer wanted the steel column in problem C to have a factor of safety of 2.5,
       what minimum compressive strength (PSI) would the steel need to demonstrate?

    e. A tensile test specimen has an effective test length of 3.75 inches. During the test, the
      specimen elongates .42 inches before fracturing. What percent elongation did this
      specimen demonstrate?


    f. An elevator cable has been rated for a maximum tensile load of 12,500 pounds. Knowing
      that the factor of safety used in selecting the cable for the elevator application was 1.7,
      what is the load at failure for this cable (in pounds)?


    g. As a garage is being cleaned out, a cylinder of unidentified metal is found. Two IBDT
      students, Ima Dweeb and Ura Goober just happen to be in the neighborhood. Ima and
      Ura take the dimensions of the cylinder and determine that it has a 5 inch diameter and
      19" length. The two students then weigh the cylinder and find that it has a total mass of
      259.89 pounds. After collecting this data, the two young academians disagree in regard
      to the type of material from which the cylinder is made. Ima insists that the cylinder is
      gold (.697 lb./in³) while Ura is convinced that the cylinder is silver (.376 lb/in³).
      Which of these two young "academians" is more likely to earn a college scholarship?
       (You must prove your answer mathematically!)


    h. A polypropylene (plastic) tow rope is being used to tow a water skier. The rope, which
        started out at 75 feet in length stretches out to total length of 84 feet. What
        percent elongation did the tow rope demonstrate?


    i. A 28 ft. long standard steel I-Beam is installed at 60 degrees F. The temperature of
      the beam may be raised as high as 125 degrees F when the furnace beneath it is in use.
      What will be the exact length of the beam when its temperature is increased to this level?


    j. A material has a density of .041 lb./in³. What is the specific gravity of this material and
      will it float, sink, or be semi-bouyant?




    k. Two pieces of material, one steel and the other polystyrene, are glued together. The steel piece is
      a rectangular solid with the dimensions 1/8" x 5" x 11". The polystyrene is also a rectangular solid with the
      dimensions 14" x 16" x 2". Knowing that the steel has a density of .284#/in³ and the polystyrene has a
      density of .0006 #/in³, determine if the assembly will float, sink, or be semi-bouyant.


2. Answer each of the following questions using full sentences:

    l. Using appropriate scientific terms, explain how it is possible for a human to lie down on
      a "bed of nails" without doing serious injury to themselves.



    m. State and explain 3 examples where a knowledge of physical stress is an essential knowledge
      for professionals in medical fields (i.e. pediatrician, orthopedist, dentist, etc.)

    n. There is an old phrase "...a little knowledge is a dangerous thing." It would seem that
      this is particularly true when it comes to understanding factors of safety. Explain why.

    o. Explain how is it possible that large ocean going vessels (ships), which are made
      of steel (that has a specific gravity approaching 8) are capable of being
      bouyant when steel itself is used as a material for ship anchors.

Assignment #8 - Stress/Strain Testing and Analysis (Group & Individual Project)

     - As a class, we will perform 3 tensile tests using the Universal Testing Machine in E3.
     - Begin this assignment by viewing several online references dealing with stress and strain.

        Click  here  to see a simple animation of a stress/strain test and the curve that develops.

Typical stress/strain curve with key points

        Click  here  to complete an exercise that will help you understand the difference between strength and stiffness.

        Click  here  to read an introduction to Young's Modulus (Modulus of Elasticity).

     - Collect all test data (load and distance between platens) individually in your notebook using the format shown below. Do not lose this data - you will be required to submit is as part of the lab.

     - Calculate all stress and strain values individually.
     - Draw one stress strain diagram with all three materials individually graphed.

Comparison of stress/strain curves for various materials

        Click  here  to see a typical stress/strain curve for a ductile thermoplastic (Lexan or polycarbonate.)

     - Use a french curve to interpolate the data points on the graph.
     - Label the essential elements of each curve using the following key and including:

                ER = ELASTIC RANGE
                PL = PROPORTIONAL LIMIT
                EL = ELASTIC LIMIT or YIELD POINT    (Click  here  to see more details about this.)
                PR = PLASTIC RANGE
                UTS = UTS (Ultimate Tensile Strength) or MAX. STRESS
                MS = MAX. STRAIN
                PF = POINT OF FAILURE or RUPTURE

     - Label the primary axes for STRESS (PSI) and STRAIN (in/in)
     - Color or pattern code the graph with a key for the materials.
     - Calculate the modulus of elasticity (Young's Modulus) for each
       material tested based on the stress/strain data calculated for each specimen.

     - Here is a reference chart of Modulus of Elasticity ranges for various materials:

Tensile Strength and Modulus of Elasticity Values for Various Materials
Material	Tensile Strength (PSI)	Mod. of Elasticity or Young's Modulus. (PSI)
Aluminum	12,000 to 63,000	10,300,000
Brass	32,000 to 88,000	12,000,000 to 17,000,000
Copper	32,000 to 66,000	17,000,000
Diamond		170,000,000
Douglas Fir	600 to 1,400	1,700,000
Steel	60,000 to 103,000	30,000,000

     - Write a lab report for this activity using the standard report format.
     - Include the graph and 3 test specimen data charts with your report.
        (Click  here  to see the lab report format.)
        
        
        
        

Assignment #9
Flowcharting Activity (Individual Project)

The Computer Programmer's Wedding Rehearsal

     - Working individually, you will create a flowchart that outlines a common, simple activity. The flowchart will detail the procedural sequence of the activity. The activity should be completed according to common, ordinary standards and accepted procedures (i.e. If you are going to make Jell-O, use water, not seltzer.)

     -Click here  to view a basic tutorial on flowcharts and associated symbols.

Procedures:

     - You must declare the topic with Mr. Patterson before starting.
     - The initial flowchart may be drawn by hand and the final flowchart will be drawn using the computer.
     - A simple solution is to use MS Word (see below) and work with the drawing toolbar.
        A palette of flowcharting symbols is included in MS Word.
     - Both the initial sketch and the final Word file must be submitted for evaluation.
     - Your flowchart must contain a minimum of 4 decision structures and 2 ultimate paths.
     - Use arrowheads to indicate the direction of the flowpath.
     - Keep the text in each element succinct, but of sufficient detail to make the flowpath understandable.
     - Every path must have a definite start and end or loop structure.
     - Use only standard flowcharting symbols to complete this task.
     - Place a title at the top of the flowchart.
     - Place your name at the top right of each page of the document.
        
        

How To Make A Flowchart

1. Determine the process to be defined. Make sure that "scope creep" doesn't appear. This occurs when you start out to flow just a certain process and then end up flowcharting multiple processes! Be concerned only with the scope of the topic you have declared.

2. Decide on the level of detail that's needed. This is important. Is a 10,000-foot level flowchart needed (something that could be seen from an airplane) or do you need one that is from a 100-foot level (the view from the top of a building)? This is called Macro or Micro Flowcharting.

3. Determine the process steps. Brainstorming can accomplish this. At this stage, it is not necessary to have the right sequence. The objective is to obtain all the steps that are thought to be taking place.

4 .Sequence the process steps. Use symbols here. I think that rectangles for basic process steps, diamonds for decisions (yes/no), and lines with arrowheads are sufficient.

5. Compare the flow chart to the actual process (in real time) for validation.

6. Identify those steps that should be targeted for elimination or improvement of the process.

Source of steps: TQIE (Total Quality in Education website)

Flowchart created using Word AutoShapes

Menu path for accessing AutoShapes in Word

"Despite the relative ease of performing flowcharting, there are some obstacles to be aware of. First, the process may not be stable, meaning, it doesn't happen the same way each time.  This is quite possible. Should you encounter this, try to define it the way you believe it is occurring or how it works the majority of the time. Another challenge is that the process is so complex, that trying to gain an understanding is difficult. The advice here is to start small by just perform flowcharting on a portion of the process." (Source: www.tqie.com)

Assignment #10 - Manufactured Product Analysis
(Individual Project)