# Strain or Tension?

 Forum topic by Surfside posted 08-16-2012 11:34 PM 713 views 0 times favorited 11 replies
 Surfside3361 posts in 917 days 08-16-2012 11:34 PM I know most woodworkers use the term tension rather than strain. In sawmillcreek.org, a thread has been trending with comments regarding which is right, strain or tension? As a non-expert to the field, I would like to ask LJ’s regarding this subject and your knowledge. What do you think? Is tension and strain the same? -- "someone has to be wounded for others to be saved, someone has to sacrifice for others to feel happiness, someone has to die so others could live"

## 11 replies so far

 bondogaposis2738 posts in 1095 days #1 posted 08-16-2012 11:57 PM I use tension to distinguish it from compression. -- Bondo Gaposis Nicky636 posts in 2836 days #2 posted 08-17-2012 12:04 AM Non expert opinion… I don’t think of tension and strain being the same in the context of wood. Strain causes a board to warp or deform in someway (e.g. as it looses moister) Tension is released when I cut a strained board, and this deforms my cutoff in someway. But what do I know. My 2cents. -- Nicky RickRogers739 posts in 1782 days #3 posted 08-17-2012 12:15 AM Tension or compression describe the load being applied to a particular item. Strain is a measure of how much that item deflects due to an applied load. JJohnston1593 posts in 2035 days #4 posted 08-17-2012 12:49 AM Strain is technically the amount of UNIT deformation (so much deformation per unit of length – think of it as “inch per inch”). The total amount of elongation or shortening is strain x the length of the member. Tension is a force; its units are units of force, like pounds. It causes a tensile stress which is a function of the cross-sectional area of the member (stress = force divided by area, for lb/sq. in.) -- "Sometimes even now, when I'm feeling lonely and beat, I drift back in time, and I find my feet...Down on Main Street." - Bob Seger Dusty5611684 posts in 2432 days #5 posted 08-17-2012 01:05 AM World English Dictionarytension (ˈtɛnʃən) — n1. the act of stretching or the state or degree of being stretched2. mental or emotional strain; stress3. a situation or condition of hostility, suspense, or uneasiness4. physics a force that tends to produce an elongation of a body or structure5. physics a. voltage, electromotive force, or potential difference b. ( in combination ): high-tension ; low-tension6. a device for regulating the tension in a part, string, thread, etc, as in a sewing machine7. knitting the degree of tightness or looseness with which a person knits [C16: from Latin tensiō, from tendere to strain] strain/strān/Verb: Force (a part of one’s body or oneself) to make a strenuous or unusually great effort.Noun: A force tending to pull or stretch something to an extreme or damaging degree.A breed, stock, or variety of an animal or plant developed by breeding.Synonyms: verb. stretch – filter – tighten – tensenoun. stress – tension – race -- I'm absolutely positive that I couldn't be more uncertain! DylanC122 posts in 1418 days #6 posted 08-17-2012 01:22 AM RickRogers has it…Strain is a measurement of how much something is stretched. That’s the engineering definition, by the way. Common woodworing context may be different. The behavior Nicky is describing (a board warping after it is cut) is something that metals to also and is cased by residual internal stress. -- Dylan C ...Seems like all ever I make is sawdust... JJohnston1593 posts in 2035 days #7 posted 08-17-2012 01:54 AM No, what he defined is deformation, and deformation and strain are not the same thing. http://www.mechatools.com/en/definition.html -- "Sometimes even now, when I'm feeling lonely and beat, I drift back in time, and I find my feet...Down on Main Street." - Bob Seger Surfside3361 posts in 917 days #8 posted 08-17-2012 01:27 PM So, when does strain apply when we deal with band saw blades? -- "someone has to be wounded for others to be saved, someone has to sacrifice for others to feel happiness, someone has to die so others could live" JJohnston1593 posts in 2035 days #9 posted 08-18-2012 12:48 AM I’m not sure what you mean. The blade manufacturer has (probably) an allowable tensile stress on the blade material. That and the cross sectional area determine the allowable tension. The strain is what it is; in this application, it doesn’t seem to me to be important to know it. I can tell you, for example, where it would be important to. I’m a bridge engineer, and sometimes, we want to know the actual stress on a member in service, so we put strain gauges on it. We measure the strain, and using these relationships between force, area, stress and strain, we can calculate the actual stress on it. -- "Sometimes even now, when I'm feeling lonely and beat, I drift back in time, and I find my feet...Down on Main Street." - Bob Seger Surfside3361 posts in 917 days #10 posted 08-20-2012 01:50 PM As you’ve mentioned that strain is the amount of unit of deformation or elongation, wouldn’t elongation or deformation happen in a band saw blade? I think this is what I was supposed to ask. -- "someone has to be wounded for others to be saved, someone has to sacrifice for others to feel happiness, someone has to die so others could live" JJohnston1593 posts in 2035 days #11 posted 09-03-2012 03:37 AM Yes, yes it would. -- "Sometimes even now, when I'm feeling lonely and beat, I drift back in time, and I find my feet...Down on Main Street." - Bob Seger