Sadeq Malakooti

As part of the NASA Convergent Aeronautics Solutions (CAS) portfolio, the Sustainable Manufacturing of Aircraft (SUMAC) project aimed to explore sustainably derived thermoplastic composites to minimize environmental impacts on an aircraft full lifecycle. For this purpose, three different potential high‐performance bioderived thermoplastics including polylactic acid (PLA), poly‐3‐hydroxybutyrate (PHB), and polyamide‐11 (PA11) were fully characterized using multiple techniques such as differential scanning calorimetry (DSC), thermogravimetric analysis (TGA), and dynamic mechanical analysis (DMA). For each resin, thermal properties (e.g., thermal decomposition characteristics, melting and glass transition temperatures) as well as viscoelastic properties (e.g., storage and loss moduli) were measured and their potential material merits for aerospace applications were investigated. Lastly, the recyclability of the resins was evaluated through multiple melting/remelting cycles and their DMA performances were compared against the initial baseline materials. Each polymer demonstrated distinct advantages for aircraft manufacturing. For instance, PHB offered high damping, PLA exhibited high stiffness, and PA11 provided strong recyclability. Overall, this work aimed to highlight a new material perspective for aerospace manufacturing by exploring biomass‐derived engineering thermoplastics.

Several ASTM and ISO standards describe the experimental procedures for measuring the normal incident acoustic impedance of samples in a standing wave tube, but they do not describe a standard sample to evaluate the performance of these experiments. Such a standard would be desirable for calibration and validation of impedance measurement systems. Ideally, such a standard would be stable, repeatable, easy to construct with readily available components, and have predictable performance. In this paper, several candidate concepts meeting the above criteria were identified, constructed, and tested. The performance of these concepts and an examination of some factors that control their performance are discussed. The impact of errors in the measurement of ambient temperature, barometric pressure, and sample placement on measurements of acoustic impedance is evaluated. Candidate concepts for potential acoustic standards are identified and discussed.

The ballistic performance of edge-clamped monolithic polyimide aerogel blocks (12 mm thickness) has been studied through a series of impact tests using a helium-filled gas gun connected to a vacuum chamber and a spherical steel projectile (approximately 3 mm diameter) with an impact velocity range of 150–1300 m s⁻¹. The aerogels had an average bulk density of 0.17 g cm⁻³ with high porosity of approximately 88%. The ballistic limit velocity of the aerogels was estimated to be in the range of 175–179 m s⁻¹. Moreover, the aerogels showed a robust ballistic energy absorption performance (e.g., at the impact velocity of 1283 m s⁻¹ at least 18% of the impact energy was absorbed). At low impact velocities, the aerogels failed by ductile hole enlargement followed by a tensile failure. By contrast, at high impact velocities, the aerogels failed through an adiabatic shearing process. Given the substantially robust ballistic performance, the polyimide aerogels have a potential to combat multiple constraints such as cost, weight, and volume restrictions in aeronautical and aerospace applications with high blast resistance and ballistic performance requirements such as in stuffed Whipple shields for orbital debris containment application.

Resin uptake plays a critical role in the stiffness‐to‐weight ratio of wind turbine blades in which sandwich composites are used extensively. This work examines the flexural properties of nominally half‐inch thick sandwich composites made with polyvinyl chloride (PVC) foam cores (H60 and H80; PSC and GPC) at several resin uptakes. We found that the specific flexural strength and modulus for the H80 GPC sandwich composites increase from 82.04 to 90.70 kN · m/kg and 6.03 to 7.13 MN · m/kg, respectively, with 11.0% resin uptake reduction, which stands out among the four core sandwich composites. Considering reaching a high stiffness‐to‐weight ratio while preventing resin starvation, 32% to 38% and 40% to 45% resin uptakes are adequate ranges for the H80 PSC and GPC sandwich composites, respectively. The H60 GPC sandwich composites have lower debonding toughness than H60 PSC due to stress concentration in the smooth side skin‐core interphase region. The ailure mode of the sandwich composites depends on the core stiffness and surface texture. The H60 GPC sandwich composites exhibit core shearing and bottom skin‐core debonding failure, while the H80 GPC and PSC sandwich composites show top skin cracking and core crushing failure. The findings indicate that an appropriate range of resin uptake exists for each type of core sandwich composite, and that within the range, a low‐resin uptake leads to lighter blades and thus lower cyclic gravitational loads, beneficial for long blades.

We present metamaterial-like aerogels that provide broadband low-frequency vibration mitigation through their self-assembled locally resonant microstructures. Simulations confirm the presence of a negative dynamic stiffness for the aerogels.