Both architected materials and granular media have been independently shown to significantly improve mechanical energy absorption by intentionally leveraging different energy dissipation mechanisms. Yet it is almost completely unknown how these two classes of materials can be combined to beneficially interact under compression to failure. Herein, we propose the concept of “architected granular media”, or AGMs, where an architected lattice is filled with granular media and show their combination can increase specific energy absorption up to 80% over the empty lattice. We experimentally characterize the quasi-static stress-strain compressional response to failure of auxetic and non-auxetic AGMs filled with different types of granular media, supported by image analysis, flowability measurements, and micro-CT. Results show that the auxetic AGMs preferentially activate the embedded granular media to increase specific energy absorption, and the embedded granular media properties dictate failure modes and stress-strain response. Finally, we show that patterned AGMs, where different granular media are filled in different portions of the lattice, can control failure in a predictable way, opening the possibility of engineered failure with AGMs. This paper demonstrates AGMs are promising for certain energy absorbing applications and could improve critical protective devices such as wave shielding, mechanical impact and crashworthiness, aerospace materials, and sports gear.

Elastomer lattice structures provide tunable mechanical properties and full elastic recovery over large strains. However, the design of elastomer lattice materials can be challenging when the manufacturing process induces geometric deformations that can significantly affect the material properties. This paper presents a method for fast, image-based measurements of geometric deformations in additively manufactured elastomeric honeycombs and the impact of these deformations on mechanical properties. A total of 55 parts were designed, fabricated, and tested; these parts have linear elastic stiffness 15.4-1422.8 kPa and plateau stress 1.4-164.3 kPa. Image measurements extract the length and thickness dimensions of every wall in every part, revealing small but random distortions that arise from the manufacturing process. An additional 10 parts were modified to have larger deformations for the purpose of the study. Machine learning models trained using the measured wall dimensions accurately predict the mechanical properties. Models that use measured wall dimensions outperform models based on design values only. A Graph Neural Network (GNN) predicts the linear elastic stiffness, plateau stress, and densification onset with 18.2 %, 16.0 %, and 3.2 % error. This method could aid designers in understanding the properties of elastomer lattice structures and the impact of manufacturing-induced deformations.

Nanoheterogenenous metallic glasses (MG) can offer improved ductility through a nanoscale modulation in their mechanical properties. However, the relationship between the modulation parameters and the mechanical behavior is not well understood. Physical vapor deposition can directly control the compositional and morphological parameters of nanoheterogeneous MGs and enables the systematic investigation of this problem. This work explores the microstructure and mechanical properties of a range of CuTa-based nanolayered amorphous/amorphous (A/A) and amorphous/semi-crystalline (A/SC) nanoheterogeneous MGs and MG composites. The first step was the identification of three microstructural regimes in CuTa, namely, a fully amorphous form (23-65 at.% Ta), a Ta-rich amorphous-crystalline composite (65-75 at.% Ta), and a Cu-rich amorphous-crystalline composite (16-23 at.% Ta). The hardness of the films increased from 6 GPa to 17 GPa with increasing Ta content. Next, a range of CuxTa1_ x/CuyTa1_y nanolayers composed of A/A and A/SC nanolayers were investigated. The hardness of all nanolayers follows the rule of mixture. A/A structures do not provide a significant increase in fracture toughness and only a minor increase in tensile ductility despite the high amplitude modulation of hardness between layers. A/SC nanolayers' hardness and toughness was higher than A/A nanolayers as well as monolithic amorphous films, but still remained below the monolithic Cu25Ta75 SC film. The results show that the design of nanoheterogeneities in MGs requires careful optimization to achieve a useful improvement in mechanical properties.

Metal nitride coatings are increasingly used in MEMS applications. The brittle nature of these coatings makes fracture one of the main failure mechanisms during operation. Therefore, quantifying the fracture toughness of nitride coatings in a reliable fashion is important to understand the failure behavior and to optimize device performance and reliability. This study investigated the fracture toughness of AlTiN coatings produced by cathodic arc evaporation, a widely used technique in the industry. Nanoindentation and microcantilever bending-based measurements indicated a fracture toughness of 6.6 and 4.8 MPa & sdot;m1/2, respectively. The lower toughness results of microcantilever bending were attributed to the columnar growth of the coating, which promoted crack propagation perpendicular to the film surface. The results provide useful data toward a better understanding of the fracture of hard coatings and give insight into the advantages and disadvantages of different measurement methods.

On-site repairs of carbon fiber reinforced polymer (CFRP) composites involve out-of-autoclave curing, which increases the defect density and reduces the mechanical properties. This work aims to understand the strength and the associated failure mechanisms of on-site repaired woven CFRP laminates through experiments and simulations. A series of wet lay-up and prepreg step repaired specimens produced according to standardized aerospace procedures were tested under uniaxial tension. Wet lay-up repair provided a strength recovery of 66%, whereas prepreg repairs maintained 76% of the original strength. Finite element modeling closely predicted the experimentally observed behavior and showed that stress concentrations due to the adhesive-adherent stiffness mismatch are the primary causes of the lowered strength. The findings provide systematic experimental data and an accurate modeling framework to design and implement effective repairs in practice.

Al-Rare Earth (RE) metallic glasses provide an effective model system to study the effect of nanocrystallites in an amorphous matrix on nanomechanical behavior. In this work, we achieved a series of Al-Tb metallic glass-crystalline composites with systematically varying crystalline content through annealing. The nanomechanical properties were characterized using micropillar compression tests and nanoindentation for as-quenched amorphous and annealed amorphous/nanocrystalline composite specimens. The promising hardness increases after annealing from 3.0 GPa to 4.6 GPa and elastic modulus increment from 68 GPa to 92 GPa were discussed in detail, considering the structural features of Al-RE marginal metallic glass formers. The increase in elastic modulus is associated with the nucleated fcc-Al nanocrystals that divide the amorphous matrix, leading to the branching of the shear bands. The correlation between the fcc-Al nanocrystals and the behavior of shear bands was discussed in detail.

This article investigates the mechanical behavior of polyamide and carbon fiber-reinforced (CFR) polyamide structures produced by Fused Filament Fabrication. CFR improves solid polyamide's tensile strength and modulus by more than 200% and 800%, respectively. The enhancement is highest in the parallel raster due to the alignment of the fibers in the printing direction. The compression tests of gyroid, honeycomb, and Voronoi cellular structures revealed the effect of geometry and fiber reinforcement on energy absorption performance. CFR gyroid infill offers the best performance with a specific energy absorption capacity reaching 10 kJ/kg and an efficiency close to 50%. Fiber reinforcement improves energy absorption by a factor of four or higher while increasing the weight by only 10%. The energy absorption capacity of the reinforced polyamide offers enormous potential for developing new lightweight load-bearing and impact-absorbing structures.

Fused deposition modeling (FDM) is a versatile additive manufacturing technique for producing polymeric parts. Incorporating a foaming agent into the filament material enables the FDM-printing of thermoplastic foams, which opens up new possibilities for achieving desired mechanical property combinations. This study explored the process-property design space of FDM-printed polylactic acid (PLA) foams. Tensile and compression specimens were produced at a wide range of printing parameters using a commercial thermoplastic filament containing a foaming agent. Increasing the nozzle temperature and decreasing the filament feed rate increased the extent of foaming. Adjustment of the nozzle temperature, feed rate, and infill ratio controlled porosity over a density range of 0.24 to 1.17 g/cm3. Tuning of the mechanical properties over an order of magnitude was demonstrated, with elastic moduli ranging from 0.24 to 3.7 GPa and tensile strength ranging from 4.2 to 34.5 MPa. The mechanical behavior closely followed the Gibson-Ashby model predictions. Foaming filaments provide a new tool for tuning the mechanical response of FDM-printed parts to achieve unique combinations of mechanical properties that are not attainable through conventional methods.

This study investigated the mechanical behavior of ZrxTa1-x (x = 21-79 at%) thin films and nanolayered films of ZrTa with modulated composition as model systems to gain insight into the hardness and toughness of metallic glasses and metallic glass nanocomposites. The monolithic films exhibit two primary micro-structures, namely, a fully amorphous form (Zr = 35-70at%.) and an amorphous-crystalline composite (21-30 at% Zr). The amorphous films show a monotonic hardness variation with composition over a wide range of 5.5 - 9 GPa. The partial crystallization of the films results in a further jump in hardness, as opposed to the general trend of softening upon crystallization. The emergence of the crystalline phase also improves the ductility of the films, as verified by nanoindentation-based fracture toughness measurements. The indentation pile-up exhibits several shear bands in the fully amorphous films, replaced by a featureless pileup zone for the case of Zr25Ta75, further verifying the superior toughness of the composite. The second part of the analysis pursued obtaining a similar toughening through fully amorphous nanolayered films of Zr35Ta65 / Zr70Ta30. The results indicate that these films provide a balanced combination of high hardness and enhanced ductility, providing an alternative route to the development of tough metallic glass coatings. Data Availability: The raw/processed data required to reproduce these findings cannot be shared at this time as the data also forms part of an ongoing study. (C) 2021 Published by Elsevier B.V.

Refractory high entropy alloys (RHEAs) are promising materials for extreme environment applications, such as high temperatures (>1000 °C), corrosion and irradiation due to the sluggish diffusion and self-healing effect. In this study, irradiation response of a novel light-weight (Ti25Zr35Nb20Hf5Ta15)95O5 RHEA with high strength and ductility has been investigated using Fe ions up to 30 local dpa at RT and 450 °C. Microstructure and mechanical properties have been examined using optical microscopy, XRD, transmission electron microscopy and nanoindentation. It has been found that the main damage consists of <111> and <100> type dislocation loops. The damage in the microstructure increases with dose at both RT and 450 °C irradiations. Besides, damage in 450 °C irradiated samples is always greater than the damage in the RT irradiated samples. Even though the hardness increase is small in the case of RT irradiations, it increases more, especially after 30 dpa in the case of 450 °C irradiations. However, the changes seem to be within the standard deviation of the hardness of unirradiated samples except for 30 dpa. Dislocation loop-induced hardening is compensated by the lattice relaxation phenomenon. Meanwhile, this alloy clearly shows a great promise for radiation resistance.

Fused deposition modeling (FDM) is one of the most widely used additive manufacturing techniques for the fabrication of polymeric parts. Earlier applications of FDM mostly utilized pure polymers such as polylactic acid (PLA) and acrylonitrile butadiene styrene (ABS). However, there has recently been an increasing demand for composite FDM filaments to obtain superior mechanical and physical properties. Fly ash (FA), a waste of coal power plants, is a promising alternative as a filler material for developing composite filaments. Due to the massive amounts of FA generated worldwide and associated environmental concerns, there has been an increasing trend in the utilization of FA particles in the polymer industry, providing a new route for FA recycling towards reducing FA’s impact on the environment. However, there has been no study to date to investigate the same route for FDM use. In this study, we incorporated 2 wt

Strengthening of nanocrystalline Al by grain boundary solute additions was investigated for a series of dilute aluminum alloys, Al-Sc, Al-Sb, Al-Cr, and Al-W with grain sizes in the range of 50-200 nm. Thermal annealing of the alloys at low temperatures led to alloy softening, but with negligible change in the grain size. The re-duction in strength can be attributed to the loss of solute in the grain boundaries arising from grain boundary diffusion and precipitation. Annealing at higher temperatures led to grain growth, but with little additional loss of strength, a result of precipitation hardening. The Al-Sc and Al-Sb alloys were additionally subjected to ion irradiation at various temperatures. These studies revealed that annealed samples regained their hardness due to solute redistribution by ion beam mixing. Alloy strength was independent of grain size between 50 and 150 nms. Irradiation-induced segregation of Sb to grain boundaries in Al-Sb further enhanced strengthening.

Traditional Al alloys have shown tremendous potential in the aerospace industry due to their attractive properties such as ductility, fracture toughness, and fatigue resistance. However, modern aerospace applications call for next-generation Al alloys with a stringent combination of properties such as high strength, low density, and excellent environmental stability. In that sense, we studied highly driven Al-Rare-Earth (RE) alloys under far-from-equilibrium conditions to investigate the possible effects of cooling rate on the expected microstructure, thus mechanical properties. Al94Sm6 was produced using a copper wheel melt spinner. XRD analysis showed the Sm is entirely trapped within the Al matrix. The heat-treated specimens resulted in the formation of the nanocrystalline Al4Sm phase embedded in the Al matrix, with a two-step precipitation sequence. The hardness values determined by nanoindentation shows that the initial supersaturated solid solution has 3.83 GPa hardness, while the heat-treated ones have 3.34 GPa. The mechanisms behind this extreme strength and ductility through solute trapping, and subsequent heat-treatments were discussed in detail using a combined study of micromechanical characterization, nanoindentation, electron microscopy, XRD, and DSC.

Mechanical failure of graphite nozzle throats is a common problem of rocket engines. The extreme operating conditions constitute the main cause of the problem, resulting in thermal shock-induced cracking. However, the exact mechanisms of crack initiation and propagation are not well-understood. This study presents a detailed investigation of the problem by combining computational fluid dynamics simulation of the supersonic flow, finite element modeling of the thermal shock, and extended finite element method-based (XFEM) analysis of the cracking behavior. The results show that most cracks initiate at the flow surface and propagate parallel to the surface in the form of Mode II cracks. Partitioning the nozzle into an assembly of graphite segments reduces the peak stresses and slows down the crack propagation and resulting failure. The efficiency of this partitioning approach strongly depends on the proper selection of clearances between the segments. The findings clarify the failure mechanisms of graphite nozzle throats and provides key information towards superior throat designs with higher fracture resistance.

Recent advances in the development of elastomeric thermoplastic filaments have enabled the production of elastomeric components using fused deposition modeling. The unique mechanical properties of elastomers and the vast design space of additive manufacturing provide new opportunities to develop structural parts with tailored mechanical behavior. Understanding the mechanical behavior of FDM-produced elastomers is an essential part of realizing these opportunities and ensuring the reliable operation of printed parts in service. This chapter presents an overview of the current knowledge about the mechanical behavior of FDM-produced elastomers. The chapter first presents some introductory information about FDM and the mechanical behavior of elastomers. The subsequent discussion presents the effects of the primary process parameters, namely, nozzle temperature, raster orientation, build orientation, and infill ratio on the mechanical properties. Finally, recent findings on elastomeric composites and cellular structures are discussed, and future research directions are proposed.

Purpose This paper aims to provide an overview of the recent findings of the mechanical properties of parts manufactured by fused deposition modeling (FDM). FDM has become a widely used technique for the manufacturing of thermoplastic parts. The mechanical performance of these parts under service conditions is difficult to predict due to the large number of process parameters involved. The review summarizes the current knowledge about the process-property relationships for FDM-based three-dimensional printing. Design/methodology/approach The review first discusses the effect of material selection, including pure thermoplastics and polymer-matrix composites. Second, process parameters such as nozzle temperature, raster orientation and infill ratio are discussed. Mechanisms that these parameters affect the specimen morphology are explained, and the effect of each parameter on the strength of printed parts are systematically presented. Findings Mechanical properties of FDM-produced parts strongly depend on process parameters and are usually lower than injection-molded counterparts. There is a need to understand the effect of each parameter and any synergistic effects involved better. Practical implications Through the optimization of process parameters, FDM has the potential to produce parts with strength values matching those produced by conventional methods. Further work in the field will make the FDM process more suitable for the manufacturing of load-bearing components. Originality/value This paper presents a critical assessment of the current knowledge about the mechanical properties of FDM-produced parts and suggests future research directions.

We report on the mechanical analysis of scarf-bonded woven fabric CFRP laminates. The study focuses on the effect of the scarf angle on the failure behavior of the repaired composite structures. Composite panel manufacturing was based on twill carbon/epoxy prepregs and followed standardized lay-up and curing procedures. We tensile tested scarf-bonded specimens with scarf angles of 1.9°, 2.8°, and 5.7°. The results show that the tensile strength decreases with increasing scarf angle. There are mainly three types of failure, depending on the scarf angle. The failure type is predominantly cohesive for 5.7°, fiber failure for 1.9°, and a mixture of these for 2.8°. Finite element analysis through cohesive zone modeling accurately predicts the experimentally observed response and provides further insight into the failure behavior. Stress concentration distribution over the bonding area plays an important role in the failure type of the repaired specimens. An additional investigation on the effects of adhesive defects showed that a defect fraction of 10% over the bond area can reduce the strength by almost 20%.

Fused deposition modeling (FDM) is a widely used additive manufacturing technique for producing polymeric parts. While most commonly used FDM filaments are PLA and ABS, nylon is a widely used thermoplastic polymer in industry. This study investigated the mechanical properties of FDM-produced specimens made of nylon and quantified the effect of process parameters such as raster orientation and nozzle temperature on the mechanical properties. As the nozzle temperature increases, specimens become stronger with higher elongations at the break. This is mainly due to the improved fusion between the layers, provided by an expansion of the heat-affected zone. On the other hand, specimens with diagonal raster orientation exhibit higher elongations than those with perpendicular and parallel raster. The findings also emphasize the synergistic effects between nozzle temperature and printing orientation, showing that optimization should consider the two parameters together. Overall, FDM can produce strong nylon parts with adequate ductility suitable for load-bearing applications. However, achieving such results requires a detailed optimization of process parameters.

Ti-6Al-4V is one of the most promising alloys for electron beam melting (EBM) of structural parts due to its outstanding properties and its extensive use in the aerospace, automotive, and energy industries. In this study, we report a detailed and systematic micromechanical characterization of additively manufactured Ti-6Al-4V parts produced via EBM. The specimens were characterized by microhardness, nanoindentation, micropillar compression, and microscratch measurements. The results show that the Ti-6Al-4V exhibits a strong indentation size effect and higher strain rate sensitivity compared to those obtained from macroscale measurements. The high scratch resistance and the high hardness of the alloy at small indentation depths suggest that the EBM-produced Ti-6Al-4V parts can provide good performance in service under sliding wear conditions.