Ensuring accuracy by force measurement and material testing is a necessary requirement in every industry. For instance, consider the force required to tap a smartphone screen or push buttons on a remote control. Most of us do these things without thinking, but even for every day devices, force measurement has to be considered.
Historically, force measurement tests were calculated by using a series of mathematical equations, Newton’s first, second and third law. In recent years, force 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 sophisticated applications.
Designing parts and components for industries such as aerospace, medical and automotive requires extremely high levels of accuracy and production errors can be costly. Stringent regulatory requirements – and high costs for failing to meet standards – ensure that components are safe, fully functional and reliable.
The AS9100 group of standards, for example, is a series of regulatory requirements that are specific to aerospace manufacturing. The regulations ensure that manufacturers produce components within a strict quality controlled environment, to guarantee reliability and safety of an aircraft. This quality assurance is particularly important for mass manufacturing environments, where busy production lines are expected to produce a high volume of precise, identical parts and components. Similarly, the 21 CFR Part 11 Electronic Signatures requirement is very important for life science applications, such as medical device manufacturers and pharmaceutical manufacturers. Following this standard, software solutions that enable measurement data traceability and documentation is critical for the operators and supervisors responsible for the applications.
Meeting these standards is not a simple task, but to simplify quality management and improve accuracy, manufacturers are choosing sophisticated force measurement and metrology systems to test the components they make. Starrett’s force measurement software, L2 Plus, for example, can provide a comprehensive analysis of a measurement test – providing exact force measurement results from simple peak load measurement to more complex break determination.
By exporting measurement data through USB or wirelessly across Bluetooth, manufacturers can access data and insight far beyond the basic figures provided by other force measurement approaches. Inputting the requirements of a part, material or component allows the software to generate high-resolution graphs based on load, distance, height and time of measurement. In addition, in the case of the Starrett L2 plus system, historical test data is archived and available to analysis 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 designing and creating components. By gaining complete control with a system like this, design engineers are less restricted and can, be more innovative with their designs. What’s more, quality control managers can rest assured that parts will meet industry standards and, as a result, are less likely to fall victim to manufacturing errors.
Material testing is another type of force measurement. The only difference is that the sample’s dimension is used to determine results. For example, a load result is called stress in material testing. Stress is the load result divided by the sample’s cross-sectional area. This is why stress has the unit pounds per square inch using imperial measurement. Using SI units, the common unit for stress is Newton per mm squared (N/mm2). N/mm2 is a mega-pascal (MPa). Stress = Force/Area. Strain is distance from force measurement. Strain is a unitless value, but is often shown as a percentage. Strain is also called % Elongation. Again, like stress, strain uses the sample’s length value. Strain is the change in length from its original length. If the sample had an original length of 1 inch (25mm) and then was pulled to 2 inches (50mm), the strain is 100%. Strain equals Ultimate Gage Length minus the Original Gage Length divided by the Original Gage Length.
For components produced with composites, material testing can be very helpful. Composites are made by combining two or more materials ‒ often materials with very different properties. Predominately, it is the advancements in polymer composites that are changing the way composites are used. Composites based on polymer continue to evolve and find their way into all kinds of products for aerospace, medical and automotive applications. Polymer composites have a high strength to weight ratio and are relatively easy and inexpensive to manufacture.
Product designers and 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 presents difficulties when establishing a coherent data set. The data are 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.
Using Starrett 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 analyze the stress, strain, load, distance and time for each material, with measurements displayed on graphs and data tables with statistics and tolerances. 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 manufacturers eager to reap the rewards of composite materials, without wasting time on endless manual testing and measurement.
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, as with easy-to-use software, such as from Starrett.
For more information: www.starrett.com
This article was authored by James M. Clinton – Product Manager Force and Material Test Products at the L.S. Starrett Company