The actuator that i have in my lab is an old manual (load controlled) actuator. In the code that i am using, it suggests that the actuator must develop a rate such that the displacement must be from 0.06 N/mm2 to 0.1 N/mm2. How can i achieve this if i only have a load controlled actuator?
As far as I understood, you need to maintain a fibre stress of .06-.1 N/mm2. You can test on trial and error basis for different load speeds (e.g., 0.1, 1, 5, etc. kN/min) and check for which you are getting the range. YOu will follow this constant speed for the remainder of your test program.
Converting load control to displacement control is a different issue. I dont think its possible. Difference in behaviour of materials in term of stress-strain curve is similar up to failure point (especially for linear response) for both tests. However, you will get different post-failure zone for load- and displacement control tests.
Hope this will help. Cheers
PS: you can check the following publication (attached)
Paul, D. K. and Gnanendran, C. T., "Characterisation of Lightly Stabilised Granular Base Materials by Flexural Beam Testing and Effects of Loading Rate," Geotechnical Testing Journal, Vol. 35, No. 5, 2012, pp. 1-12, http://dx.doi.org/10.1520/GTJ104183. ISSN 0149-6115
Thank you for your answer. A trial & error using LVDT is the most suitable way.
Even if you do the trial and error using LVDT, it wont give you correct result. Rather it may vary widely depending on many factors-- most important of them are machine to sample stiffness ratio (lower the ratio, higher is error) and the rate of loading. The best thing you can do, break some specimens/samples of similar materials to see at what range it would typically fail. Now while testing the actual specimen/sample -- while you see it goes close to the estimated peak load-- be alert, and while the load start decreasing , at that immediate point control the machine to reduce the load significantly so that you can capture the descending branch. For this too, you need a very stiff machine (comparable to specimen). And again the results are still approximate.
Dear
I agree with the above answers that you can go for trial and error and check which load magnitude will give you the required deformation using LVDT.
Both techniques of repeated stress or repeated strain may be implemented as per the international standards, there will be a variation in the shape of (deformation-load cycles) among the two testing techniques.
Dear Abidin,
pl check it.
http://ascelibrary.org/doi/10.1061/%28ASCE%29CC.1943-5614.0000726
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