Force measurement testing for composite materials

According to modern archaeology, one of the earliest examples of a composite material was the carefully soaked layers of linen and plaster used for the Egyptian practice of mummification. Composites are certainly not a new concept, however the latest advancements in composite technology are changing the way these materials are designed, tested and used in manufacturing.

Here, John Cove, Marketing Manager of test and measurement specialist, Starrett, explains the complexities of modern composites, the software needed for effective test and measurement applications and the future of the composite market.

The importance of force measurement testing

Force measurement testing is an essential process for product designers and manufacturers to gain insightful data and create high quality and ergonomic products. As consumers, we are accustomed to applying a certain amount of force to complete everyday tasks. Even simple motions, such as turning the key in a cars ignition or pressing a button on a remote control, requires a very specific amount of force to be applied.

From an engineer’s perspective, the amount of force required to complete these tasks is not coincidental. In fact, these requirements are carefully planned during the product development process. Whether this is to accommodate human ergonomics or to meet product safety regulations, manufacturers will complete a thorough force measurement process for every product they design.

Historically, force was calculated by using a series of mathematical equations, known as Newton’s first, second and third law. Even more recently, force measurement testing has been limited to handheld metrology devices. While faster than lengthy calculations and more accurate than guesswork, these machines do not provide the levels of precision needed for more complex materials.

Accuracy is imperative for the development of high quality and ergonomic goods, especially in a climate where end users have come to expect seamless performance from both consumer and industrial devices or machines. Modern force measurement systems need to meet the exact requirements of research scientists, design engineers, quality managers and the technicians responsible for material characterisation, verification and validation of products.

Often, there is confusion as to the difference between force measurement and materials testing. In force measurement, the interest of the engineer is to determine the peak load and extension of a material. Force measurement is usually conducted in a high volume production environment. Materials testing, on the other hand, requires a higher level of precision. Materials testing will often take place in an engineering or research laboratory, using precision load cells and an extensometer for elongation measurement.

Materials testing is used to determine the physical and mechanical properties of raw materials and collect an array of materials data: such as tensile strength, compression, flexure, friction, tear, peel, adhesion, shear, ductility insertion and shear strength. Force measurement systems are ideal for product testing of finished goods such as, plastics, packaging, electronic components, metals and, in this case, composites.

Composite complexities

Composites have come a long way since the ancient Egyptian era. Predominately, it is advancements in polymer composites that are changing the way these materials are used in industry. The rising popularity of polymer composites is no surprise. These materials have a high strength to weight ratio and are relatively easy and inexpensive to manufacture.

Unfortunately, in applications like construction and rail, composites have a poor reputation compared to their steel predecessors. By their nature, composites are comprised of many variations; different fibres, resins, stack materials and fillers. As a result, composites are subject to vigorous test and measurement processes.

Naturally, product designers and original equipment manufacturers (OEMs) want to ensure their polymer composite can withstand the force that will be placed on it. They also need to know if the material will stretch or elongate and pinpoint its exact breaking point. The major objective of any test and measurement process is to build a coherent set of materials data, but in the case of composite materials, one size rarely fits all.

Software solutions for composite testing

The diversity of composites raises difficulties when establishing a coherent data set. The data is likely to be completely unique to each sector, product, application and area. The most common tests for tensile strength (MPa or PSI) are tensile chord modulus of elasticity (MPA or PSI), tensile strain (%), Poisson’s ratio and transition strain (%). However, when testing composite materials, the application should not pre-suppose any prior knowledge of which measurements are required.

Take Starrett’s L3 software as an example, rather than providing pre-set data, the user creates a test method for the specific material. Using this technique, a product designer or OEM can analyse the stress, strain, load, distance and time for each material, with measurements displayed on graphs and data tables with statistics and tolerances. In the case of Starrett’s L3 software, tests can use tension, compression, flexural, cyclic, sheer and frictional forces.

The unfamiliarity of composite materials requires mechanical testing throughout the entire design and production process. Consequently, automation is becoming increasingly attractive to those manufacturers eager to reap the rewards of composite materials, without wasting time on endless manual testing and measurement.

In a utopia, automated software packages should be capable of creating an interface that links hardware and software to improve processes from the lab, right up to the plant floor. For force measurement software applications, programming experience should be optional, not essential, which is exactly as it with Starrett's easy to use software.

By exporting measurement data through USB or wirelessly through Bluetooth, manufacturers can access high-resolution graphs based on load, distance, height and time of the measurement. In addition, in the case of the Starrett L2 plus system historical test data is archived and available to analyse at a later date, helping speed up future tests and navigating potential problems or errors.

This intelligent software increases the accuracy of force measurement, while also improving precision for engineers producing components. By gaining complete control with a system like this, design engineers are less restricted and in turn, can be more innovative with the products they design. What’s more, quality managers can improve customer satisfaction as they understand the products they are producing are unlikely to fall victim to manufacturing errors.

Much like the wider automation industry, where most devices, from an inverter to a suite of robots, use simple languages and interfaces, automation in the software package should be comprehensible for any engineer, with as little as half a day of software training.

One of the major roadblocks of composite materials is that mass manufacturing data is not readily available. As some composites are not yet fully scalable materials, testing and measurement will play a major role in the research that creates data. This challenge could not be more notable for some of the composite technologies that are still in development, such as graphene related materials (GRP).

Looking to the future: graphene

The market for graphene is still in its infancy, but it’s incredible strength to weight ratio means that this material is already being hailed as one of the most disruptive technologies of our time. For the composite market, there is no doubt that using graphene could open up a host of new possibilities. However, the introduction of this technology will have a significant impact on the testing and measurement process.

Stronger than a diamond yet a million times thinner than a human hair, the properties of graphene are astounding. The technology is already being used in various ways, such as in the manufacturing of glass reinforced plastic (GRP) composite road plates being used by utilities and infrastructure firms during necessary road works. Major automotive manufacturers are also beginning to run research groups to test graphene-based composites for use in new vehicles. Regardless of its obvious advantages, using graphene to its fullest potential is not without its challenges.

Research has shown that dispersing a small amount of graphene into polymer composites can dramatically improve a material’s tensile strength, elastic modulus and electrical and thermal conductivity. However, because these GRMs are not yet fully scalable, product researchers and designers are yet to develop a comprehensive understanding of the technology.

The potential for graphene to reinforce a composite relies on a trade-off between the properties of the matrix material and the graphene itself. As a result, force measurement testing will need play a major role in ensuring simultaneous stiffness, strength and toughness of GRMs during the manufacturing process.

Currently, mass manufacturing data for graphene composites is unavailable and there is no tried and tested method for the largescale production of graphene-based products. While there is no denying that graphene composites are going to be a major trend, if GRMs are to dominate the market, they will require thorough testing to the same standard as established materials.

Composite materials are continually developing and the introduction of graphene adds another layer of complexity. As GRMs are completely new to the market, engineers will not be familiar with potential properties so will be unsure of what tests are required to measure tolerances. This is purely due to the fact that there will not be any existing data to draw from. As engineers begin to incorporate graphene into new composites, the challenge of accurate measurement can be overcome by using intelligent testing and measurement software.

Naturally, the software to test GRMs will test for common measurement data, such as tensile strength, tensile chord modulus of elasticity, tensile strain and transition strain. In the case of Starrett’s L3 software, a graph will automatically be generated using the test data provided, allowing the engineer to measure any point or segment on the graph for tension, compression, flexural, cyclic, shear and frictional forces.

Without thorough testing of newly developed GRMs, these materials may fall short of their potential and engineers utilising the expensive material could miss valuable opportunities. The properties of graphene are fascinating and the possibilities it affords the composite market is exponential. However, to truly deliver design engineering excellence using graphene, innovation in measurement must come first.

In today’s competitive manufacturing environment, product designers and OEMs cannot afford to ignore the clear benefits of using composite materials. The sophistication of composites has come a long way since the ancient Egyptian era and naturally, the testing and measurement requirements have evolved too.