WEST LAFAYETTE, Ind. \u2014 Much like baking the perfect cake involves following a list of ingredients and instructions, manufacturing energetic materials \u2014 explosives, pyrotechnics and propellants \u2014 requires precise formulations, conditions and procedures to ensure they are safe and perform as intended.<\/p>\n\n\n\n
Because any small tweaks or environmental changes can dramatically alter how energetic materials function, Purdue University engineer Monique McClain<\/a> is developing state-of-the-art tools and methods to control these materials\u2019 behavior throughout the manufacturing process and down to the particle level.<\/p>\n\n\n\n McClain, a Purdue assistant professor of mechanical engineering, specializes in the \u201cupstream\u201d or earlier manufacturing stages, such as selecting binders with unique properties to hold energetic particles together and determining how they are mixed to create the final formulation. She focuses on how manufacturing alters the structure and mechanical properties of an energetic material and, in turn, how those changes affect performance and sensitivity.<\/p>\n\n\n\n \u201cAn energetic material\u2019s manufacturing history, from beginning to end, strongly determines how it behaves during combustion or detonation,\u201d McClain said. \u201cWe want to ensure that each step is catered toward the material and its intended use so that we\u2019re getting a final product that functions in the way we expect.\u201d<\/p>\n\n\n\n Much of McClain\u2019s body of work focuses on additive manufacturing or 3D printing of energetics. Traditionally, energetic materials have been manufactured using processes such as casting or milling, which prioritize efficiency and scalability. But while these methods are ideal for large batch production, customization is difficult, thereby limiting innovation and compromising on optimal performance.<\/p>\n\n\n\n Additive manufacturing, on the other hand, gives researchers the freedom to experiment with complex geometries and tune specific properties such as burn rate and blast shape.<\/p>\n\n\n\n For instance, McClain and her research team<\/a> design intentional defects \u2014 referred to as pores \u2014 to either increase or decrease the likelihood of ignition when materials are subjected to various conditions such as friction, impact or extreme temperatures. Additive manufacturing makes this possible because researchers can customize a 3D printer\u2019s nozzles and program it to print specific shapes and patterns.<\/p>\n\n\n\n \u201cPores and defects are often inevitable, but we can control how and where they show up,\u201d McClain said. \u201cWhen we focus on the microstructure of these materials, we can deliberately select particle sizes or compaction schemes to produce preferred pore distributions that enable the behaviors that we want to see.\u201d<\/p>\n\n\n\n Additive manufacturing also makes it easier to experiment with multiple types of materials. In addition to her work with pores, McClain explores how energetic particles adhere to various binders through the 3D-printing process and how to print propellant materials made of multiple materials with disparate characteristics.<\/p>\n\n\n\n In a study<\/a> published last spring, McClain and her team looked at adhesion between two polymers with different mechanical properties \u2014 a stiff thermoplastic and a soft elastomer \u2014 that have been combined into one structure. They found that the 3D-printed surface texture and type of thermoplastic greatly affected how well the two materials blended and held together.<\/p>\n\n\n\n \u201cThis study provides a framework and method for studying adhesion of dissimilar materials. This is important because no such guide \u2014 and, in turn, little data \u2014 on this topic previously existed,\u201d McClain said. \u201cThe ability to print energetics made of multiple materials gives us even more options for controlling behavior and improving safety.\u201d<\/p>\n\n\n\n Although 3D printing is a major part of McClain\u2019s work, she also explores how to improve more traditional manufacturing methods.<\/p>\n\n\n\n McClain developed a patent-pending method<\/a> for manufacturing a polymer-bonded explosive (PBX) molding powder that saves time, eliminates potential hazards and reduces manufacturing waste. McClain disclosed this technology to the Purdue Innovates Office of Technology Commercialization<\/a>, which has been applied for a patent through the U.S. Patent and Trademark Office to protect the intellectual property.<\/p>\n\n\n\n The method involves mixing energetics with a binder that\u2019s been partially cured or hardened prior to compaction within a mold. McClain found a sweet spot of time \u2014 approximately eight hours \u2014 where the binder becomes solid enough to prevent leakage during compaction, but not so hardened that it becomes brittle and prone to cracking.<\/p>\n\n\n\n \u201cWe aimed to provide a repeatable, tunable method for fabricating solid energetic composites, like PBX, with uniform mechanical and chemical properties,\u201d McClain said. \u201cWe succeeded in developing a streamlined set of steps where researchers can make slight adjustments based on their goals for the final product.\u201d<\/p>\n\n\n\n While following the proper steps of the energetics manufacturing process helps to ensure a safe, well-designed final product, external conditions also influence its performance.<\/p>\n\n\n\n According to McClain, factors such as room temperature can dramatically affect a material\u2019s printability and behavior.<\/p>\n\n\n\n \u201cEnvironmental control matters much more than many people expect,\u201d McClain said. \u201cYou could print the same mixture twice in the same day and they might behave in completely different ways if something like the temperature or humidity level in the room changed.\u201d<\/p>\n\n\n\n Ultimately, McClain advocates for a holistic approach to manufacturing rather than one driven by technology advancement. She wants researchers to avoid \u201cforce fitting\u201d materials into a particular machine or method and instead consider which geometries and properties are required to create the desired effect.<\/p>\n\n\n\n \u201cIf you need a complex internal structure, additive wins. If you need a highly dense mixture or a large batch of material, conventional methods are often more appropriate. To get the best of both worlds, we can also incorporate molding and milling alongside 3D printing,\u201d McClain said. \u201cAs long as we understand every aspect of the process, from selecting material all the way to packaging and storing them, we\u2019ll be able to make the best and safest choice.\u201d<\/p>\n\n\n\n McClain\u2019s research is sponsored by the U.S. Air Force Office of Scientific Research\u2019s Young Investigator Research Program and the Army Research Office Energetic Materials Basic Research Center. McClain conducts her research at Maurice J. Zucrow Laboratories<\/a>, the largest academic propulsion lab in the world.<\/p>\n\n\n\n Purdue University is a public research university leading with excellence at scale. Ranked among top 10 public universities in the United States, Purdue discovers, disseminates and deploys knowledge with a quality and at a scale second to none. More than 106,000 students study at Purdue across multiple campuses, locations and modalities, including more than 57,000 at our main campus locations in West Lafayette and Indianapolis. Committed to affordability and accessibility, Purdue\u2019s main campus has frozen tuition 14 years in a row. See how Purdue never stops in the persistent pursuit of the next giant leap \u2014 including its integrated, comprehensive Indianapolis urban expansion; the Mitch Daniels School of Business; Purdue Computes; and the One Health initiative \u2014 at https:\/\/www.purdue.edu\/president\/strategic-initiatives<\/a>.<\/p>\n\n\n\nAbout Purdue University<\/h2>\n\n\n\n
Paper<\/h2>\n\n\n\n
Material and surface roughness effects on adhesion of thermoplastic-elastomeric interfaces for dissimilar material 3D printing
<\/em>npj Advanced Manufacturing
DOI: https:\/\/doi.org\/10.1038\/s44334-025-00023-2<\/a><\/p>\n\n\n