Ensuring accuracy by force measurement and material testing is a necessary requirement in most every industry, especially orthopedic and medical parts manufacturing where the highest quality control is crucial. For instance, consider the force required to bend a knee that has been replaced, or tests were calculated by using a series of mathematical equations, known as 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 medical requires extremely high levels of accuracy. Production errors can be very costly. Stringent regulatory requirements — and high costs for failing to meet standards — ensure that components are safe, fully functional, and reliable.
The 21 CFR Part 11 Electronic Signatures requirement, for example, is very important for life science applications such as medical device 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. Force measurement software 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 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, historical test data is archived and available for 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 that are designing and creating orthopedic 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
Material testing is another type of force measurement. The only difference is that the sample’s dimension is used to determine the 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 in. (25 mm) and then was pulled to 2 in. (50 mm), the strain is 100 percent. 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 polymers continue to evolve and find their way into all kinds of products for aerospace and medical applications.
Polymer composites have a high strength-to-weight ratio and are relatively easy and inexpensive to manufacture. Carbon fiber composites, including carbon fiber reinforced polymer, is desirable for lower limb orthopedic components due to its excellent load capability combined with being light weight.
Product designers and OEMs want to ensure that their polymer composite can withstand the force that will be placed on it. They also need to know whether 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 presuppose any prior knowledge of which measurements are required.
Using advanced material testing software as an example, rather than providing preset 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 force measurement and material testing software.
This article was written by James M. Clinton, Product Manager for Force and Material Test Products at The L.S. Starrett Company, Athol, MA. For more information, visit here .
