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Testing Military-Grade Adhesive in Extreme Loading Conditions

Military performance requirements for adhesives have been traditionally derived to fulfill niche defense needs in harsh operational environments with little consideration for dual-use commercial potential.

Figure 1. Bonded tensile butt joints clamped in alignment fixtures undergoing oven cure at 140°C. A thermocouple is placed at the bond line and a spring is used compensate for mismatches in thermal expansion.

The term “military-grade” can have a variety of meanings that are perspective dependent. In 2014, Ford Motor Company emphasized the term heavily in advertising campaigns to garner consumer acceptance for the transition from steel to aluminum in the body of their flagship F150 model. As cited by Ford, “Engineers selected these high-strength, military-grade aluminum alloys because of the metals’ unique ability to withstand tough customer demands.” From this point-of-view, military-grade implies superior performance. However, the bureaucratic and logistical barriers required for certification to military-grade acceptance levels per DoD performance requirements can also be perceived as impediments to innovation and the transition of fundamental science into tangible product. This is in-part due to the legacy age of many DoD performance standards dating to the 1950s and 1960s when the US military peaked in technology market share and was responsible for approximately two-thirds of domestic research and development (R&D) and one-third of global R&D.

In 2023 the commercial private sector provides the overriding funding stream for technology development for primarily non-military applications. Since the “golden age” of DoD-derived performance specifications the interactive roles between requirements and innovation are now understood to be dependent on their timings to product life cycle, which is typically ignored universally across the materials domain. Traditional DoD adhesive specifications are measures of late life cycle quality assurance for low-risk bonding applications with long-term historical usage and well-understood design allowables.

Military-grade certification for commercial industry can also imply a high degree of qualification effort for a limited defense market with marginal dual-use consumer return on investment. This is an unfavorable position for DoD, as commercial industry requires a sustainable business model to produce defense-relevant materials.

MIL-PRF-3266210 represents a forward-looking and “anticipatory” specification to deliberately coincide with the timing of emergent, and potentially lucrative, adhesive technologies by encouraging, high-risk/high-payoff commercial product innovation. The hypothesis of this approach is that defining DoD technology drivers in terms of industrially relevant performance metrics, with high non-DoD profit potential, will decrease transition time and increase DoD access to sustainable commercial products with leading state-of-the-art properties. Prior to the release of MIL-PRF-32662 in 2020, no adhesive, with bonded structural armor as the primary focus, had bridged the “valley of death” from basic research to qualified product.

The technical challenge posited by Army ground vehicle applications is the need for concurrent high-strength and high-fracture toughness, which is a difficult material property trade-space for adhesives. PPG Industries (PPG) was the first commercial adhesive manufacturer to meet MIL-PRF-3266210 Group 1 requirements with the development of their PR-2930 one-component epoxy adhesive. This adhesive targets the Army ground vehicle requirements put forth in MIL-PRF-32662 but is also formulated for compatibility with commercial automotive assembly line bonding processes. The next question to be answered is can the performance value of military-grade be quantified using a benchmark of an extreme testing condition referenced by the commercial sector?

The adhesive bonding joint configuration used for this study was a tensile butt joint with a 40 cm 2 surface area for bonding, which is specified by Guinness World Records. The most recent record was set in 2019 to suspend a 17,200 kg (37,919 lb.) construction vehicle at a height of 1 m for 1 h. In this work, the world record hoist and static hold conditions were mimicked using a laboratory loading frame. Results show that an adhesive meeting MIL-PRF-32662 Group 1 requirements readily sustains 22,680 kg (50,000 lb.) of static loading for 1 hour, for a 32 percent increase against the current world record benchmark. The results offer a potential quantitative measure for military-grade and show the utility of leveraging anticipatory military performance standards to lead material advancements.

This work was performed by Daniel Deschepper and a team of researchers from the Army Research Laboratory. For more information, download the Technical Support Package (free white paper) below. ARLTR-9915

Topics:
Adhesives and sealants Adhesives/Sealants Aerospace Alloys Aluminum Aluminum alloys Coatings & Adhesives Manufacturing & Prototyping Materials Metals Metals Research and development Test & Measurement
This Brief includes a Technical Support Package (TSP).
Document cover
Testing Military-Grade Adhesive in Extreme Loading Conditions

(reference ARLTR-9915) is currently available for download from the TSP library.

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    Aerospace & Defense Technology Magazine

    This article first appeared in the August, 2024 issue of Aerospace & Defense Technology Magazine (Vol. 9 No. 5).

    Read more articles from this issue here.

    Read more articles from the archives here.

    Overview

    The document titled "Testing Military-Grade Adhesive in Extreme Loading Conditions" presents a comprehensive study on the performance of military-grade adhesives, particularly focusing on their application in high-stress environments. Authored by experts from the DEVCOM Army Research Laboratory and PPG Industries, the report addresses the evolving landscape of adhesive technology, especially in the context of military applications.

    Historically, the Department of Defense (DOD) has relied on performance standards that date back to the mid-20th century, a time when it dominated research and development (R&D) in technology. However, as the commercial sector has taken the lead in funding technology development, the DOD faces challenges in adapting to modern innovations. The report highlights the need for updated specifications that align with current technological advancements and market demands.

    A key focus of the study is the MIL-PRF-32662 specification, introduced in 2020, which aims to encourage the development of high-risk, high-reward adhesive technologies. This specification is designed to facilitate the transition of innovative products from basic research to qualified applications, addressing the so-called "valley of death" that many technologies face. The report emphasizes the importance of defining DOD technology drivers in terms of industrially relevant performance metrics, which can enhance the sustainability of commercial products with military applications.

    The document outlines the testing protocols used to evaluate the adhesives, including surface preparation, adhesive application, curing conditions, and mechanical testing. The results demonstrate the adhesives' performance under extreme loading conditions, which is critical for applications such as structural bonding in military vehicles and equipment.

    In conclusion, the report underscores the necessity for the DOD to adapt its standards and specifications to foster innovation in adhesive technologies. By aligning military requirements with commercial viability, the DOD can ensure access to cutting-edge materials that meet both defense and civilian needs. The findings aim to inform future research and development efforts, ultimately enhancing the performance and reliability of military-grade adhesives in demanding environments.

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