The Testing Times

These grips are used to test seat belts and webbing up to 100mm thick. seat belts have interesting properties, they have to cushion the shock of a crash without injuring the passenger of the car at low speed stops. In a collision it has a precise elastic limit, meaning that it stretching slightly to diffuse the shock, goes beyond its elastic limit, becomes plastic then holding it's passenger without breaking, there is a great deal of force involved in this process (which is why these grips are rated to 100 kN ...) The testing can be quite explosive as the belt stores a great deal of energy before failing. By exerting a tensile force on the belt it is possible to see how it will behave. One of the important features of this grip is that it is self tightening. The specimen is feed through the grips in a specific manner as not to damage the belt. A damaged belt can dramatically affect its ability to protect the passenger, and once it has been stretched to it's elastic limit and

This grip is designed to meet the very strict guidelines set within the ASTM D143 standard. I have mentioned this standard before, it is one of the most demanding standards available for wood specimens. One of the most important tests when it comes to the structure of wood is how it reacts in tension. As wood can be very strong in tension it's is necessary to 'profile' the sample (cut the wood into a specific shape) so that the region undergoing test is uniform, in the middle and weaker than the grip or piece of wood the grip is holding onto. It also needs to be smaller to allow an extensometer to be added to measure the small changes in the length of the sample. This grip is essentially self-aligning, the sample slotting into the two fingers.

Articulated 4 Point Bend Test for Ceramic Samples. Used for testing the smallest ceramic samples 1.5mm x 2.0mm x 20mm. The test calls for articulated anvils that are free to move as the sample deforms. The problem is how to hold the anvils in place before loading the sample. The answer is it’s all done by magnets. The anvil is attracted towards the end of the bar magnet. The magnets are positioned so that the anvil will return to the start position as soon as load is removed. In case you loose the odd one, we supply a bag of spares!

A flexural test tells the tester how much force a specimen can withstand in the middle when supported at a distance (or its flexibility!). This test supports the specimen between two loose fitting ‘rollers’, the distance apart of which can be set for a specific test or specimen size. Once the sample is in place the anvil can be brought down just above the specimen. A variety of tests can then be performed. The specimen can be flexed a certain number of times to judge it’s elasticity or plasticity over a given time. The specimen could be flexed until it breaks, it could be flexed for a specific time and the responding force measured. This is a Heavy Duty system, which has been designed to suite the U-Series 100 kN System . It has a travel of 400mm from centre (800mm overall) and Ø10mm rollers. This can all be recorded in the software and multiple specimens can be tested.

Sylvia Hillier, the Textiles expert here at Tinius Olsen has her own blog, she is very knowledgable and a really nice person to boot! If you've got any textile related issues go here! http://www.testingtextiles.com/sylviablog.php

Some of the more destructive tests that our systems are designed to perform can be quite violent, the forces and materials used can have some explosive results. It is often important to guard the rest of the room or the user from flying shrapnel. We produce guards for these reasons, as the U-Series is over 2 metres tall and a large footprint; the U-Series needs to have a huge guard. We made the guard a close rectangular fit around the system; it is free standing although there are some mounting points to attach it to the system. aluminium section and composite sheet make the frame up, which is a very strong (and heavy) structure. It has two wrap around doors and polycarbonate windows that allow the user to see and control the test. For safety the control unit and an emergency stop have been placed on the right hand door. I can safely say that this is verging on architecture, rather than engineering!

Imagine trying to hold a piece of fibre insulation (the stuff in your roof that stops the heat escaping) in a clamp and then pulling it apart using a tensile test, how on earth do you do it? It’s fibrous, comes in different thicknesses, breaks of easily into chunks… Well the answer is Nails, and lots of them. This is the most effective way to distribute the load across and through this particular sample, this means that the test specimen isn’t overly damaged when you grip it. If the sample is ‘waisted’ properly (like an hour glass), it will break in the weakest spot, not by the grip. This is a technique used time and again with all kinds of samples. You want to see how the material will break under load, not how the grip breaks it, and then the load pull it apart. As there are a lot of nails it’s quite hard to push them through the top surface of the specimen (Imagine trying to nail 20 nails at once into something soft. It might be soft but there is a lot of friction to overcome). To