Ensuring accuracy by force measurement and material testing is a necessary requirement in every industry. 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 everyday devices, force measurement must 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, it has been limited to handheld metrology devices. While faster than lengthy calculations and more accurate than guesswork, these do not provide the levels of precision needed for sophisticated applications.

Designing parts and components for industries such as aerospace, medical, and motor vehicles 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, ensure that manufacturers produce components within a strict quality-controlled environment, to guarantee reliability and safety of an aircraft. This 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. Following this standard, software solutions that enable measurement data traceability and documentation are 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 ranging from simple peak load measurement to more complex break determination.

By exporting measurement data, manufacturers can gain insight 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. With the Starrett L2 plus system, historical test data are archived for analysis later, helping speed future tests and navigate potential problems or errors.

Intelligent software increases force measurement accuracy, while improving precision for engineers designing and creating components. As design engineers gain this insight, they are less restricted and can be more innovative. Meanwhile, quality control managers can be assured parts will meet industry standards and are less likely to have 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 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, distance from force measurement, is a unitless value but often shown as a percentage. Strain is also called % elongation. Again, like stress, strain uses the sample’s length; strain is the change from its original length. If the sample had an original length of 1" (25mm) and was pulled to 2" (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 is often necessary since composites are made by combining two or more materials, frequently with very different properties. Advancements in polymer composites that are changing the way composites are used, and composites based on polymer, continue to evolve and find their way into aerospace, medical, and motor vehicle applications. Polymer composites have a high strength-to-weight ratio and are relatively easy and inexpensive to manufacture.

Product designers and original equipment manufacturers (OEMs) want to ensure their polymer composite can withstand the force 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.

The modulus of elasticity represents the stiffness of the material under test. In tensile applications, this modulus is often called Young’s Modulus and is the relationship between stress and strain within the proportional limit.
The maximum stress observed from the strain-strain curve.

Software solutions

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, 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 relative 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 to the plant floor. For force measurement software applications, programming experience should be optional, not essential.

The L.S. Starrett Co.

About the author: James M. Clinton is product manager for force and material test products at The L.S. Starrett Co. He can be reached at 978.249.3551 or jclinton@starrett.com.