In this article we will provide you a thesis report on Whittmore-Petrenko Proving ring or simply proving ring. In this project on proving ring we will provide you background history on proving ring, types of rings, materials required, design, construction and working of  Proving ring. The project covers Strength of materi

als among various other subjects of mechanical engineering.

Abstract

Proving ring is a force transducer concept designed, analyzed and developed to be used in laboratory experiments to measure forces. The elastic behavior of the proving ring was analyzed using Castigliano’s second theorem and the results were found to be about 1% accurate.

The proving ring is a metal ring equipped with means of measuring deflection when under load. The concept of proving ring was created originally by Whittmore and Petrenko at the US National Bureau of standards.

Introduction

Force transducers are commonly used in engineering applications like weighing scales, verification of material testing machine, thrust measurement etc. Ring shaped transducers provide an ease in manufacturing and are widely used for the measurement of force.

The proving ring is a elastic metal ring with a means of measuring deflection when it is under load. It is used to measure force. The ring is currently used in laboratory exercises and in research projects in fluid mechanics.

History of Proving Ring

With the recent trend in industrialization techniques there is a demand for light weight materials for efficient structural design with improved strength. However, without a means of testing new materials so produced mishaps are likely to occur.

Keeping these things in mind Whittmore and Petrenko came up with improved Proving ring with a means to measure deflection when under load. The design was built in NATIONAL BUREAU OF STANDARDS in early 1920.

What is Proving Ring

Proving ring is a force measuring device. It is a steel ring made up of correct steel alloy and properly manufactured to perform nearly as elastic member. When forces are applied along the diameter of the ring, there is certain change in dimension of ring along diameter knowing which corresponding force value is calculated using the formula:

δ=PD^3/EI

Where,

P= Force applied

D= diameter of the ring

E= modulus of elasicity

I= moment of inertia

The external and internal bosses are integral part of the ring to assure long term reliability. The rings are machined from special forged steel and are properly heat treated to give maximum sensitivity and durability. The dial gauge fitted is 0.002 mm sensitive.

Types of Proving Ring

1. Clamped Bosses Proving Ring:

 

These have clamped bosses as shown in the figure with range of 0.5 KN to 100 KN

2.Integral Proving Ring:

These rings have integral loading bosses forged and machined along with the ring. These rings are manufactured up to 3000KN.

3. Tension-Compression Proving Rings:

These rings can be used both in tension as well as compression. The bosses are integral. The capacity of these rings varies from 1 KN to 100 KN.

How Proving Ring Works:

Proving ring provides an effective, accurate and repeatable alternative to measure force once calibrated accurately. The metal ring flexes under applied load and if fabricated properly then its diameter will change or deflect versus load in a linear change versus loading relationship. The ring stretches vertically for tensile forces and shrinks vertically when compressed. A properly manufactured ring behaves as nearly elastic element with highly linear relationship between applied force and resultant deflection.

So with the help of above mentioned formula we can easily calculate force applied once we accurately measure the deflection produced in the ring due the the corresponding force.

So how to measure the deflection one would ask, right?

For this it is equipped with a micrometer and vibrating read.

Once the load is applied the vibrating reed is tapped which causes it to vibrate producing audible sound. Next step is to screw the micrometer till it dampens the vibration changing the sound to distinguishable buzz. This buzz sound is distinct and repeatable which you will never miss.

The reading on the dial of micrometer will show the deflection produced in the ring and with the help of chart that comes with the ring, you can easily convert this deflection value into respective force value. So you need not worry about doing those lengthy calculations again and again, the manufacturers have got it covered for you.

Some new proving ring systems combine the micrometer with digital read out saving your laborious task of seeking the chart again and again for conversion. Benefit of technology as you can point out.

Now lets take a look into material used for proving ring

Material Requirement for Proving ring:

The ring is made of mild steel with 0.25% Carbon,  0.4-0.7% manganese, 0.1-0.5% Silicon and some traces  of other elements such as Phosphorous.

Mild steel or carbon steel is a term used for range of carbon steels having good strength and can be easily bent, worked or welded into variety of shapes.

Well, that ends the thesis report on Proving Ring. Please comment below if you have any queries regarding this or about any other project that you would like us to discuss here.

To know about calibration objective and techniques click here.