Strain gauge to measure wood expanasivity.

In summary, the conversation revolves around measuring thermal expansion of wood using strain gauges. The use of a Wheatstone bridge circuit schematic and an appropriate strain gauge is recommended. Recommendations for strain gage suppliers and installation guides are provided. It is noted that strain gages may not be the most suitable method for measuring thermal expansion in wood and alternative methods such as extensometers are suggested. Several references from the Forest Products Lab and ASTM are also mentioned as resources for further information.
  • #1
billsalmon
Hi!
Im measuring how much wood expands in different temperatures using a strain gauge.
do i need to use a wheatstone bridge circuit schematic? or else how do i heat up the wood without spoiling the strain gauge. Actually how will i heat up the wood anyway?
Also how would i draw a diagram to show the apparatus? and how do you attach the strain gauge to the wood- is it with ps adhesive?
Your help is much needed and very much appreciated if you know.
thanks.
 
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  • #2
Have you used a strain gage before? Or do you have one in mind. I would expect the supplier has some instructions on setting up a gage, and perhaps some recommendations on what gage to use with what material.

Let me check around.
 
  • #3
Yes normally a Wheatstone works however, many strain gage modules have the Wheatstone bridge build in (Labview, NI). I always had trouble calibrating strain gages or having them to do what the factory said (probably my fault). Be careful because they might be sensitive to temperatures. "Each strain gage wire material has its characteristic gage factor, resistance, temperature coefficient of gage factor, thermal coefficient of resistivity, and stability".

http://www.omega.com/literature/transactions/volume3/strain.html
 
  • #4
i need help on this too...i dnt knw homework 2 start at all!and i dnt knw homework to draw a diagram for the apparatus and even a circuit diagram
 
  • #5
has anyone finished this??!
 
  • #6
The site provided by jaap de vries is a good reference.

Here is another - http://www.kyowa-ei.co.jp/english/technical_info/ch1_2.htm
Strain Gage Installation Guide Chapter 1 & 2

It has diagrams of gages and circuits.


Now it seems unusual to measure thermal expansion with strain gages, since the traditional purpose is to measure mechanical strain which is different from thermal strain. Normally, one would match the thermal expansion coefficient of the gage with the material, which effectively eliminates (or at least minimizes) the thermal strain. In the case where one wants to measure thermal strain, then one needs a strain gage with a very low (as much as possible) thermal expansion coefficient. There are apparently strain gages for wood and concrete, but I believe these are primarily designed for measuring mechancial strain.

Presumably the wood is enclosed within an oven? Otherwise I'd recommend an extensometer, which is used in tensile test experiments.
 
  • #7
In general, if it deals with wood properties and mesasurement, it is reported at the FPL.
It is the very best place to start.

'Wood as an Engineering Material' from the Forest Products Lab in Madison WI:
http://www.fpl.fs.fed.us/documnts/fplgtr/fplgtr113/

Chapters, index, etc. and/or the whole book are there in pdf.

Astronuc is right: strain gages are not usually the standard way to deal with this, AFAIK.
Some other older references I have floating around:

Kubler, H.; Liang, L.; Chang, L.S. 1973. Thermal expansion
of moist wood. Wood and Fiber. 5(3): 257-267.

Weatherwax, R.C.; Stamm, A.J. 1947. The coefficients of
thermal expansion of wood and wood products. Transactions
of American Society of Mechanical Engineers. 69(44):
421–432.

ASTM. 1997. Standard methods for testing small clear
specimens of timber. ASTM D143. West Conshohocken,
PA: American Society for Testing and Materials.
 

1. What is a strain gauge and how does it measure wood expansivity?

A strain gauge is a device that measures changes in the length or shape of an object. It works by converting mechanical strain (deformation) into an electrical signal. To measure wood expansivity, the strain gauge is attached to the surface of the wood and as the wood expands or contracts due to changes in moisture or temperature, the strain gauge detects the resulting strain and converts it into an electrical signal.

2. How accurate are strain gauges in measuring wood expansivity?

The accuracy of a strain gauge in measuring wood expansivity depends on a few factors, such as the quality of the gauge, the type of wood being measured, and the environmental conditions. Generally, strain gauges are quite accurate and can measure changes in length or shape down to a few microns.

3. Are there any limitations to using strain gauges to measure wood expansivity?

Yes, there are a few limitations to using strain gauges to measure wood expansivity. The main limitation is that the surface of the wood must be flat and smooth for the strain gauge to accurately measure the strain. Additionally, strain gauges may not be suitable for measuring large pieces of wood or wood that is constantly exposed to extreme environmental conditions.

4. Can strain gauges be used to measure wood expansivity in real-time?

Yes, strain gauges can be used to measure wood expansivity in real-time. The electrical signal produced by the strain gauge can be connected to a data logger or computer, allowing for continuous monitoring of wood expansivity over time.

5. How can the data collected from strain gauges be used in wood research or industry?

The data collected from strain gauges can provide valuable insights into the behavior of wood under different environmental conditions. This information can be used in wood research to better understand the properties of different types of wood and how they respond to changes in moisture and temperature. In industry, strain gauge data can be used to optimize wood processing methods and ensure the quality and durability of wood products.

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