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Up Topic Welding Industry / Inspection & Qualification / Tensile Testing Machine Results
- - By vb (*) Date 12-03-2003 04:51

I am taking a welding inspector course, and in the module, it explains the dial on a tensile testing machine, usually has two pointers. One reading gives the yeild point, and the other reads the ultimate stress.

I am under the understanding that the yeild point is - the maximum force given, providing it will shape back to the original size (elasticity).

The module states "Initially, both displays show the same reading, but if the load drops, one display stays at the maximum value. This allows yield point and maximum load to be recorded easily."

The way I picture this is the machine pulls to maximum force - which gives an ultimate strength reading (maximum load), and then when it breaks (aka neck), it takes that reading too - (breaking stress point).

This is confusing me, as I can't see a yield point being parallel to the breaking point. Do I have a completely wrong understanding in my mind? And if not, how is the yield point measured?

Thanks in advance,
Parent - By billvanderhoof (****) Date 12-03-2003 07:05
As you begin to load a mild steel sample- At first stress is proportional to strain so the plot on the stress strain diagram is linear (the elastic range). At some point (the elastic limit, or yield point) the material begins to stretch more per unit of increased stress than before. It also begins to "neck" and the plastic deformation begins to work harden it. At first the necking predominates and results in a portion of the plot which is horizontal or has a slight negative slope. Then work hardening begins to predominate and the plot regains it's positive slope (increasing strain results in increasing stress). This continues for some time until the maximum work hardening is attained. Then necking predominates again, The slope of the plot flattens, usually becomes negative for a time, and the sample breaks.

I assume that a modern testing machine has some embeded intelligence to determine the elastic limit. Old time machines required you to take periodic readings, plot on paper and determine elastic limit by observation of your plot.

Hope this helps
Parent - - By thirdeye (***) Date 12-03-2003 07:26
The yield point is the load that causes a marked increase in extension without an increase in the load. At this point the material is starting to permanently deform. In other words, the material is going from elastic to plastic.

The two methods for determining yield point are the Drop of the Beam Method and the Total Strain Method.

Hope this helps.
Parent - - By vb (*) Date 12-03-2003 07:58
Thanks to both of you! Its so much easier to absorb information when you understand it!! :) Have yourselves a great night,

Parent - By thcqci (***) Date 12-03-2003 18:13
Well said Bill. The test sample is supposed to be loaded slowly; at a controlled rate (load/minute max.). When done correctly, the primary needle will stall at the point when the sample hits the yield point. The second needle is just a follower needle that will stop at the maximum load displayed by the primary needle. Often the load will drop by an observable amount below the yield point and then the load will begin to build again until the ultimate load is reached. Older machines had a gauge face that was about 2' in diameter to be able to distinguish a load of 0.1% F.S. Older machines also may have had paper chart recording capability, otherwise you had to observe and record this (yield) point yourself. It is not always a definitive point when observing it manually. Also, extensiometers could be physically clamped to the sample to meaure the length (0.001" increments) that the sample stretched until it reached the yield point (at which point the extensiometer must be removed or be destroyed when the sample breaks). Some extensiometers would be connected to the paper chart (to draw a stress vs. strain curve) and some were manually read on a gage face. Modern electronic equipment has many more loading and recording capabilities and will load the sample at the given rate and draw the chart straight out of a computer. Sometimes I don't miss the good old days.

To learn more, start browsing at one of these sites of force application testing equipment:

Hope this helps draw a picture you can try to imagine.
Parent - - By G.S.Crisi (****) Date 12-03-2003 19:23
Hi Vicky,
as you say, old tensile test machines, also called Amsler machines from the name of their inventor, have two pointers. One is black and the other is red. They move onto a scale graduated in units of force (kilograms force or pounds force in the old machines). When the machine is started and begins to apply load on the sample, both pointers rotate slowly together. The test goes on, passing by the all of the stages described by the gentlemen who had posted their answers to your question, until the sample breaks.
At this point, the black pointer goes back to zero, showing that the test is ended, while the red pointer remains where it was, so that the machine operator can read the ultimate tensile load, i.e., the load under which the sample broke, which will be used to calculate the ultimate tensile strength, i.e., the ultimate tensile load divided by the cross sectional area of the sample.
All of this is true for the old Amsler machines, like the one we have here at Mackenzie University. Modern machines are fully computerized and are graduated in SI units of force, i.e., kN (kilonewtons). You don't need to do anything, they do everything for you. But this is a luxury we can't afford in third world countries.
Giovanni S. Crisi
Sao Paulo - Brazil

Parent - - By vb (*) Date 12-04-2003 08:04
Thanks for all of the information! The links are great - and quite updated from the test equipment I am reading about! 3rd world countries have the advantage where they can keep the training updated with their speed of technology :) !! As I am finding out, technology has seemed to take quite a climb in North America, and think this must have a direct improvement on the standards and quality which takes place with todays welds.

I used to think welding was an "old school" trade, but have been shown that it is quite opposite, and is implementing the robotics, computers, digital, and sensor devices quite nicely!

And to think, I thought these modules covered everything, twice!! There is an abundance to learn in this trade, it is like a world of its own!

Thanks again for the links and knowledge,
Parent - - By jwright650 (*****) Date 12-04-2003 12:16
What you have described is what I find fascinating about this forum, the field of welding is so large and growing by leaps and bounds, that one person couldn’t possibly know all there is about it. Therefore this forum is a great place to bounce questions off people that may have touched different aspects of this field. I rely heavily on this forum and the help everyone here brings with each post. I find that most are as eager to share as I am eager to learn, and that makes for very interesting reading. I’m associated with such a small portion of the processes that make up this field and I want to see more and experience more of what this field has to offer. My travelings have been close to home and I just haven’t had the opportunities to see first hand much of what gets discussed here in the forum. I pray that people will continue to share their knowledge and experiences as they have since I’ve been participating in this forum for the past little while.
Many thanks to those who have.
John Wright
Parent - By Pitt Date 01-29-2019 02:04
Textile Tensile Testing Machine is designed to test a wide range of materials in tension, bursting, tear, elongation, constant load, elastic, thread slip, peeling and other mechanical properties. Tensile Strength Tester complies with ISO 13934.1/2, ISO 13935.1/2, ISO 9073.3/4, etc. For more information, welcome to click on
Up Topic Welding Industry / Inspection & Qualification / Tensile Testing Machine Results

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