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Creep Deformation Apparatus

Instrument cover photo.

This documentation covers part number 10-0000034.

Overview

The Creep Deformation Apparatus is a lab activity that demonstrates the physics of how materials like rock and ice can deform by slowly creeping. We can learn about their properties by simulating and observing creep, and deriving flow laws. It is able to measure and record the dispacement of samples, and can be used to collect data for later analysis, as well as for simple qualitative demonstrations.

What's in the box

Upon receipt of your unit, unpack the contents of the box and inspect all parts for any damage incurred during shipping. Immediately report any missing parts or damage to Leeman Geophysical for replacement.

  • Creep Apparatus
  • 6 In. Utility Caliper
  • Calibration Tool
  • USB Mini-B 2.0 Cable
  • Wax Cylinder Pack (x10 samples)
  • Bearing Retainer
  • 6-32, 1/8" Set Screw (x3)

Assembly Instruction

Hazards Summary/Required PPE

  • Choking Hazard, Small Parts
  • Pinching Hazard

Included Materials

  • Base Plate
  • Top Plate
  • Mass Plate
  • Standoffs (4x)
  • Shaft
  • Shaft Bushing
  • Bushing Retainer
  • Board
  • Linear Potentiometer
  • 10-32 x ¾” Screws (8x)
  • 10-32 x ½” Screw (1x)
  • 4-40 x 3/16” Screws (6x)

Tools Required:

  • 9/32” Hex Wrench (not included)
  • 3/32” Hex Wrench (not included)

Assembly

  1. Unpack the materials needed for assembly. Make sure that all the components are included in your kit.

  2. Install the standoffs in the base plate using (qty 4) 10-32 x ¾ screws as shown. Ensure the screw heads are countersunk in the plate.

    Instrument cover photo.

  3. Install the potentiometer and board to the top plate using the included 4-40 x 3/16” Screws. (The potentiometer must be installed square to the top plate to prevent measurement error.)

  4. Attach the assembled top plate to the bottom plate so that the board and potentiometer are on the bottom. Use (qty 4) 10-32 x ¾” screws.

    Instrument cover photo.

  5. Press the shaft bushing into the top plate. Make sure it is seated completely.

    Instrument cover photo.

  6. Install the bushing retainer on the bottom side of the top plate and tighten the set screw to secure it.

  7. Install the shaft to the mass plate using a 10-32 x ½” Screw as shown. The shaft should fit tightly into the pocket on the mass plate.

    Instrument cover photo.

  8. Slide the shaft into the bushing on the top plate. A light coating of white lithium grease can be applied to the shaft to prevent friction.

  9. Assembly is now complete.

Calibration

This guide will walk you through the calibration process for the Creep Deformation Apparatus.

Required Equipment

  • Calibration Step tool
  • USB Mini B
  • Calipers

The calibration procedure requires the use of a serial terminal. For these instruction we recommend the CoolTerm software. The list below shows all required programs and the links to find them.

Calibration Procedure

  1. Plug the device into your computer using the USB Mini B cable.
  2. Open the CoolTerm Program and select the Options tab.
  3. Make sure your device is plugged in and then select the Re-Scan Serial Ports button
  4. Select the correct port and then set the Baudrate to 115200 and then press OK
    CoolTerm options.
    After you close this window, select Connect in the main window. The terminal should now start showing data once a second.
  5. Next you will want to take the calibration tool and set it underneath the weight plate as pictured. In all caps typed the following command into the terminal.
    SETCAL 1.0
    NOTE: This command must, be in all caps, include the space, and confirmed with the enter key.
    calibration tool position.
  6. Under the Connection Tab, select Capture to Text/Binary File.
    Once you select start, It will ask you where you want to save the data to. Save the data CSV somewhere convenient for you. (i.e. Desktop) Your data is recording, in about ten second intervals, slide the Calibration tool back one step. After the first four steps of the calibration tool have been recorded for ten seconds, select stop.
    recording data.
  7. Open up a blank google sheets and import the CSV file. Your data should be inserted to the first two columns. Create a graph of this data under the insert tab.
    importing Data to Sheet.
  8. Open the Creep Calibration Calculator. Measure the calibration tools first 4 larges steps and enter those values, greatest to least, in the Displacement column. Using The graph you just created, hover your mouse over each step and enter the most common value for each step into the blue highlighted section of the calculator spreadsheet.
    The calculator graph should now have the correct calibration line. Print the page and keep that sheet and the calibration tool with its corresponding Creep Apparatus.
    Creep Apparatus Calculator.
  9. Navigate back to CoolTerm where your data should still be coming in once per second.
    In this terminal, you will type the command SETCAL x.xxxxxx
    The Calibration number you will use in place of the x.xxxxxx is located in the red circled number pictured below in the creep apparatus calculator. It must be entered as a decimal value, not it scientific notation.
    Calibration Number.
  10. This concludes the calibration procedure. To checkout that the calibration has been applied properly, type the command SHOW
    SHOW command.

Teachers Guide

Introduction

Rocks in the Earth can deform in many different ways, but the main distinction often made is if the deformation is brittle or ductile. Brittle deformation occurs in the cold upper crust where rocks are squeezed and store energy like springs. They keep storing more and more energy until they fail and break. This is the mode of deformation associated with things like earthquakes. Ductile deformation on the other hand is the slow movement of material, often associated with hot rocks under extreme pressures deep within the planet. Creep deformation is associated with tectonic scale deformation, flow of the Earth’s mantle, and more.

There are even different styles of creep such as diffusion and dislocation creep. Diffusion creep is generally associated with higher temperature deformation and is the movement of vacancies in a crystal’s structure through the material. Dislocation creep is the movement of a dislocation or imperfection in the crystal and generally is the dominant type of creep at lower temperatures. Dislocation creep doesn’t depend on the grain size of the material, but diffusion creep does.

Since different materials melt at different temperatures, we talk about how “high” or “low” the temperature is relative to the melting point of the material. The ratio of the current temperature of the material to its melting point is called the homologous temperature.

\[T_H = {T(K) \over T_mp(K)}\]

Similarly, we often do not want to worry about the absolute length of a sample, but we care much more about its change in length relative to its size. For example, shortening a football field by a meter would hardly be noticeable, but shortening your desk by a meter would be! To describe length change relative to the size of something, scientists use a quantity called strain. Strain is defined as the change in length divided by the initial length. The strain rate is the change in strain over time. For example a sample that was at a strain of 0.01 initially, then at 0.06 after 10 minutes would be experiencing a strain rate of 0.005 strain/minute.

Dislocation creep is described as a “power law” relationship, meaning that it works in a non-linear way. It relates the strain rate of a material under a load to the stress and material/physical properties through the use of a “stress exponent”.

\[\dot\epsilon=A\sigma^mexp({-Q_c \over RT})\]

There are several types of tests that we can run on a material - they involve different imposed sets of loading conditions called boundary conditions. We can either apply a constant load to a sample and see how it deforms and creeps under that load, or we can apply a constant crushing motion to the sample (called a constant displacement or constant strain rate) and measure the force that results from that. Both tests should produce the same results, but due to the properties of materials certain types of tests are often easier to perform on certain materials. We will be using the constant load test, often referred to as a “dead weight” test since we apply a given load and leave it there for the duration of the test.

Assuming that the temperature, materials, and load remain constant we expect to see a sample strain in a predictable way over time. First, the sample loads elastically, like a spring. This is recoverable deformation - if you remove the weight, the sample springs back. Next the curve becomes more shallow in the transient state. In this state deformation is becoming permanent as creep begins. Finally, the curve reaches a constant slope. The sample strain rate is constant and this represents the steady-state creep of the material.

Lab Activity

Accessories

Wax Core Packs (2-0000262)

A pack of 10 wax cores for use with our Creep Deformation Apparatus in the classroom! Don’t run out mid-semester. We custom cast each core in-house to ensure a consistent and quality lab experience for your students.

Revision History

Date Changes
April 2024 Moved Various Documentation to MkDocs Format