Showing papers by "Marc A. Meyers published in 2017"
TL;DR: The bioinspired design and applications of synthetic functionally graded materials that mimic their natural paradigms are revisited and the emerging processing techniques needed to replicate the biological gradients are described.
494 citations
TL;DR: It is proposed that the excellent strain hardening ability gives rise to remarkable resistance to shear localization, which makes this material an excellent candidate for penetration protection applications such as armors.
Abstract: The mechanical behavior of a single phase (fcc) Al0.3CoCrFeNi high-entropy alloy (HEA) was studied in the low and high strain-rate regimes. The combination of multiple strengthening mechanisms such as solid solution hardening, forest dislocation hardening, as well as mechanical twinning leads to a high work hardening rate, which is significantly larger than that for Al and is retained in the dynamic regime. The resistance to shear localization was studied by dynamically-loading hat-shaped specimens to induce forced shear localization. However, no adiabatic shear band could be observed. It is therefore proposed that the excellent strain hardening ability gives rise to remarkable resistance to shear localization, which makes this material an excellent candidate for penetration protection applications such as armors.
154 citations
TL;DR: This model elucidates the tensile response of the α-keratin fibers and identifies the possible transformation to β-sheet structure of keratin under tension, which affects the ductility of hair.
96 citations
TL;DR: In this paper, the complementary features between the avian bone and feather are reviewed for the first time, and provide insights into nature's approach at creating structures optimized for flight, revealing a novel aspect of the feather vane.
92 citations
TL;DR: In this paper, the authors used non-equilibrium molecular dynamics simulations to characterize the ductile tensile failure of a model body-centered cubic metal, tantalum, over six orders of magnitude in strain rate.
85 citations
TL;DR: In this paper, the Zener-Hollomon equation is modified to describe the mechanical response of the ultrafine-grained titanium over the strain rate range 10−5 to 103 s−1.
77 citations
TL;DR: The results provide compelling insights into pressure/shear amorphization and propose a route to fabricate gradient semiconducting nanostructures using lasers.
Abstract: Gradient nanostructures are attracting considerable interest due to their potential to obtain superior structural and functional properties of materials. Applying powerful laser-driven shocks (stresses of up to one-third million atmospheres, or 33 gigapascals) to germanium, we report here a complex gradient nanostructure consisting of, near the surface, nanocrystals with high density of nanotwins. Beyond there, the structure exhibits arrays of amorphous bands which are preceded by planar defects such as stacking faults generated by partial dislocations. At a lower shock stress, the surface region of the recovered target is completely amorphous. We propose that germanium undergoes amorphization above a threshold stress and that the deformation-generated heat leads to nanocrystallization. These experiments are corroborated by molecular dynamics simulations which show that supersonic partial dislocation bursts play a role in triggering the crystalline-to-amorphous transition.
55 citations
14 Mar 2017-Materials Science and Engineering A-structural Materials Properties Microstructure and Processing
TL;DR: The use of high-power pulsed lasers to probe the response of materials at pressures of hundreds of GPa up to several TPa, time durations of nanoseconds, and strain rates of 10 6 −10 1 ° ǫ s −1 is revealing novel mechanisms of plastic deformation, phase transformations, and even amorphization as discussed by the authors.
Abstract: The use of high-power pulsed lasers to probe the response of materials at pressures of hundreds of GPa up to several TPa, time durations of nanoseconds, and strain rates of 10 6 –10 1 ° s −1 is revealing novel mechanisms of plastic deformation, phase transformations, and even amorphization. This unique experimental tool, aided by advanced diagnostics, analysis, and characterization, allows us to explore these new regimes that simulate those encountered in the interiors of planets. Fundamental Materials Science questions such as dislocation velocity regimes, the transition between thermally-activated and phonon drag regimes, the slip-twinning transition, the ultimate tensile strength of metals, the dislocation mechanisms of void growth are being answered through this powerful tool. In parallel with experiments, molecular dynamics simulations provide modeling and visualization at comparable strain rates (10 8 –10 10 s −1 ) and time durations (hundreds of picoseconds). This powerful synergy is illustrated in our past and current work, using representative face-centered cubic (fcc) copper, body-centered cubic (bcc) tantalum and diamond cubic silicon as model structures.
55 citations
TL;DR: The structural differences between the three scales correspond with the attack of their predators, and show refined mechanisms which may be imitated and incorporated into superior bioinspired and biomimetic designs that are specialized to resist specific modes of predation.
Abstract: We compare the characteristics of the armored scales of three large fish, namely the Arapaima gigas (arapaima), Latimeria chalumnae (coelacanth), and Atractosteus spatula (alligator gar), with specific focus on their unique structure-mechanical property relationships and their specialized ability to provide protection from predatory pressures, with the ultimate goal of providing bio-inspiration for manmade materials. The arapaima has flexible and overlapping cycloid scales which consist of a tough Bouligand-type arrangement of collagen layers in the base and a hard external mineralized surface, protecting it from piranha, a predator with extremely sharp teeth. The coelacanth has overlapping elasmoid scales that consist of adjacent Bouligand-type pairs, forming a double-twisted Bouligand-type structure. The collagenous layers are connected by collagen fibril struts which significantly contribute to the energy dissipation, so that the scales have the capability to defend from predators such as sharks. The alligator gar has inflexible articulating ganoid scales made of a hard and highly mineralized enamel-like outer surface and a tough dentine-like bony base, which resist powerful bite forces of self-predation and attack by alligators. The structural differences between the three scales correspond with the attack of their predators, and show refined mechanisms which may be imitated and incorporated into superior bioinspired and biomimetic designs that are specialized to resist specific modes of predation.
54 citations
TL;DR: The organization of collagen fibrils into flat fibers was identified and incorporated into a constitutive model that reproduces the mechanical response of skin, which can be used in the design of synthetic skin and skin-like structures.
48 citations
TL;DR: An investigation of the shaft from seagull primary feathers is presented, elucidate the hierarchical fibrous and porous structure along the shaft length, and correlate the tensile and nanomechanical properties to the fiber orientation, finding that the composite design produces synergistic strengthening and toughening to the feather at a minimum of weight.
TL;DR: It is uncovered that, given the same area, square cross sections show higher bending rigidity and are superior in maintaining the original shape, whereas circular sections ovalize upon flexing.
Abstract: Only seldom are square/rectangular shapes found in nature. One notable exception is the bird feather rachis, which raises the question: why is the proximal base round but the distal end square? Herein, it is uncovered that, given the same area, square cross sections show higher bending rigidity and are superior in maintaining the original shape, whereas circular sections ovalize upon flexing. This circular-to-square shape change increases the ability of the flight feathers to resist flexure while minimizes the weight along the shaft length. The walls are themselves a heterogeneous composite with the fiber arrangements adjusted to the local stress requirements: the dorsal and ventral regions are composed of longitudinal and circumferential fibers, while lateral walls consist of crossed fibers. This natural avian design is ready to be reproduced, and it is anticipated that the knowledge gained from this work will inspire new materials and structures for, e.g., manned/unmanned aerial vehicles.
TL;DR: Finite-element analysis is successfully employed to correlate the applied compressive force to tensile breaking strength for the eggs, and the influence of geometric ratio and microstructural heterogeneities on the shell's strength and fracture toughness is established.
Abstract: Avian eggshells may break easily when impacted at a localized point; however, they exhibit impressive resistance when subjected to a well-distributed compressive load. For example, a common demonst...
TL;DR: The disulfide bonds in the matrix are experimentally identified as one source of the strain-rate sensitivity and viscoelasticity in α-keratin fibers and are identified as an important part of the knowledge of the overall mechanical properties of these biological materials.
TL;DR: An elastic model of a circular ring reinforced by horizontal and vertical struts is developed to explain the compressive stiffening response of the ring caused by differently oriented struts.
Abstract: Almost all species of modern birds are capable of flight; the mechanical competency of their wings and the rigidity of their skeletal system evolved to enable this outstanding feat. One of the most interesting examples of structural adaptation in birds is the internal structure of their wing bones. In flying birds, bones need to be sufficiently strong and stiff to withstand forces during takeoff, flight, and landing, with a minimum of weight. The cross-sectional morphology and presence of reinforcing structures (struts and ridges) found within bird wing bones vary from species to species, depending on how the wings are utilized. It is shown that both morphology and internal features increases the resistance to flexure and torsion with a minimum weight penalty. Prototypes of reinforcing struts fabricated by 3D printing were tested in diametral compression and torsion to validate the concept. In compression, the ovalization decreased through the insertion of struts, while they had no effect on torsional resistance. An elastic model of a circular ring reinforced by horizontal and vertical struts is developed to explain the compressive stiffening response of the ring caused by differently oriented struts.
13 Jan 2017
TL;DR: In this paper, the authors simulate strong shock waves in nanocrystalline tantalum using atomistic molecular dynamics simulations, for particle velocities in the range 0.35-2.0 km s−1.
Abstract: We simulate strong shock waves in nanocrystalline tantalum using atomistic molecular dynamics simulations, for particle velocities in the range 0.35-2.0 km s−1, which induce pressures in the range 20-195 GPa. Our simulations explore strain rates in the range 108 s−1 - 1010 s−1, and lead to a peak strength in the range 3-15 GPa. Nanocrystalline tantalum exposed to strong shock waves demonstrates deformation enabled by concomitant dislocations, twinning, and grain boundary activity at a variety of particle velocities. Twinning is observed for a mean grain size of 7 nm, starting at around 32 GPa, in disagreement with models which predict a Hall-Petch behavior for twinning, i.e. a twinning stress scaling with grain size d as d−0.5, and supporting the presence of an inverse Hall-Petch effect for twinning at small grain sizes.
TL;DR: In this paper, high pressure torsion (HPT) was applied to an extruded magnesium WE43 alloy and the evolutions of microstructure and mechanical properties were investigated in detail.
Abstract: Disks of an extruded magnesium WE43 alloy are processed by high-pressure torsion (HPT) and the evolutions of microstructure and mechanical properties are investigated in detail. Excellent grain refinement is achieved by HPT processing with a reduction in grain size from an initial value of ?12??m to a final value of ?200–300?nm after 10 turns. The microhardness increases significantly with HPT processing but low hardness values are recorded at the centers of the disks. The tensile strength initially increases and then decreases while the elongation decreases. Observations of the fracture surfaces reveal a corresponding transition of the fracture mode from ductile to brittle.
TL;DR: In this article, the authors proposed a method by which the h-index of individual researchers is extended to evaluate the performance of engineering departments, where the authors measured the collective productivity of the department members.
Abstract: A method is proposed by which the h-index of individual researchers is extended to evaluate the performance of engineering departments. For a specific department, the h-index of each faculty is plotted against the number of years since the first publication. The plot is linearized and the slope is determined, which we term Departmental Productivity Index. This index represents the collective productivity of the department members. The statistical analysis is applied to two years: 2008 and 2017. This slope is correlated with the ranking of the department from USNW the highest being 0.99 and lowest increasing to 0.5. For MSE departments, the same trend is observed: in 2008, they vary from 1.36 to 0.51, while in 2017 they range from 1.89 to 0.61. There is a systematic difference between Materials Science and Engineering and Mechanical Engineering Departments, the latter having dp-indices that are in average 30% lower than the former ones. This might be a reflection of the greater resources available nationally for materials research and of the service role that many ME departments have in Engineering Schools. The increase in dp-indices in the nine-year span (2008–2017) results from the rise in individual h-index for researchers, which reflects greater emphasis on research, increased collaborations, and an evolving research landscape. An additional observation that is revealed by this statistical analysis is that the difference between first and third tier departments decreased from 2008 to 2017, a reflection of the ‘democratization’ of research through a more equitable distribution of resources and talent. This method is also suggested to be an effective quantitative measure of departmental and faculty member performance.
TL;DR: In this article, the effect of barbules on the feather vane's ability to capture air was investigated with guineafowl, pelican, and dove feathers, and the vane was found to have directional permeability.
Abstract: In bird flight, the majority of the wing surface consists of highly refined and hierarchically organized feathers. They are composed of barbs that stem from the feather shaft and barbules that branch from barbs, forming a rigid feather vane. Barbules provide adhesion within the vane through an interlocking hook-and-groove mechanism to allow for the effective capture of air. This functional adhesive can reattach if structures unfasten from one another, preventing catastrophic damage of the vane. Here, using pelican primary feathers as a model material, we investigate the in-plane adhesion and stiffness of barbules. With guineafowl, pelican, and dove feathers, we determine the effect of barbules on the feather vane's ability to capture air. The vane is found to have directional permeability, and the effect of detaching barbules on the feather's competency is determined to be a function of barb dimensions. Interestingly, barbule spacing is found to vary within a narrow 8–16 µm range for birds weighing from 4–11 000 g (hummingbird to condor). Additionally, bioinspired barbules are fabricated through additive manufacturing to study the complexities of the vane. Barbules are underexplored structures imperative to the adeptness of the feather in flight, with the potential to provide bioinspired aerospace materials.
13 Jan 2017
TL;DR: In this article, a large-scale non-equilibrium molecular dynamics simulation of the tensile failure of tantalum is presented, where several loading schemes including flyer plate impact, decaying shock loading via a frozen piston, and quasi-isentropic (constant strain-rate) expansion are employed to span tensile strain-rates of 108 to 1014 per second.
Abstract: Ductile tensile failure of tantalum is examined through large scale non-equilibrium molecular dynamics simulations. Several loading schemes including flyer plate impact, decaying shock loading via a frozen piston, and quasi-isentropic (constant strain-rate) expansion are employed to span tensile strain-rates of 108 to 1014 per second. Single crystals of 〈001〉 orientation are specifically evaluated to eliminate grain boundary effects. Heterogeneous void nucleation occurs principally at the intersection of deformation twins in single crystals. At high strain rates, multiple spall events occur throughout the material and voids continue to nucleate until relaxation waves arrive from adjacent events. At ultra-high strain rates, those approaching or exceeding the atomic vibrational frequency, spall strength saturates near the maximum theoretical spall strength.
TL;DR: The fracture resistance of African pangolin scales is examined using single edge crack three-point bend fracture testing in order to understand toughening mechanisms arising from the structures of natural mammalian armors.
Abstract: Pangolin scales form a durable armor whose hierarchical structure offers an avenue towards high performance bio-inspired materials design. In this study, the fracture resistance of African pangolin scales is examined using single edge crack three-point bend fracture testing in order to understand toughening mechanisms arising from the structures of natural mammalian armors. In these mechanical tests, the influence of material orientation and hydration level are examined. The fracture experiments reveal an exceptional fracture resistance due to crack deflection induced by the internal spatial orientation of lamellae. An order of magnitude increase in the measured fracture resistance due to scale hydration, reaching up to ~ 25 kJ/m2 was measured. Post-mortem analysis of the fracture samples was performed using a combination of optical and electron microscopy, and X-ray computerized tomography. Interestingly, the crack profile morphologies are observed to follow paths outlined by the keratinous lamellae structure of the pangolin scale. Most notably, the inherent structure of pangolin scales offers a pathway for crack deflection and fracture toughening. The results of this study are expected to be useful as design principles for high performance biomimetic applications.
TL;DR: JMRT is now the highest-ranking Latin-America-originated materials journal and is a truly global venue, with over 50% of the articles from the US, Europe and Asia.
Abstract: We are elated to announce that JMRT has been approved by Science Citation Index and that its articles published from 2013 on (volumes 2–6) are already listed in the Web of Science. This approval follows a rigorous process in which the journal was evaluated sequentially; only the leading journals are included. This auspicious news is enhanced by the ISI Impact Factor received for 2016, a most impressive 2.359. This number puts JMRT among the elite materials journals, ahead of many traditional venues known in the community. JMRT is also an open access journal and this enhances the visibility of the contributions. This wonderful trajectory, which started in 2012 with the founding of the journal by Horacídio Leal Barbosa Filho (CEO of the Brazilian Metallurgical, Materials and Mining Association, ABM) and Nelson Guedes de Alcântara (its first Editor-inChief), is a reflection of the dedicated and competent work by our Editors, Area Editors and Advisory Board. A special appreciation is due to Mirian Chakkour Nunes, who was involved with the journal all the way from its inception. JMRT is now the highest-ranking Latin-America-originated materials journal and is a truly global venue, with over 50% of the articles from the US, Europe and Asia. We stated in the 2013 editorial entitled ‘Global Science and Technology: Past, Present and Future,’ which marking JMRT’s founding (2013, vol. 2, p. 1): The proud tradition of Materials Science in Brazil is well served by this new journal. As Brazil emerges as a leading global nation, the necessity for a journal of global reach was clear. This initial goal has been reached and we feel that our mission is accomplished. The Brazilian Company of Metallurgy and Mining, CBMM, and the ABM have played a pivotal and visionary role by supporting the journal since its inception. Many challenges lie ahead but this transformative moment reinforces the role of Brazil as an emerging country with a splendid materials tradition and future.
TL;DR: The Third Pan American Materials Congress as discussed by the authors was held in San Diego, with TMS in the role of host society, and a program covering a variety of materials science topics was created based upon input from leading scientists and engineers representing eight countries and the nine international materials, metals and minerals societies.
Abstract: The Third Pan American Materials Congress marked the success of an initiative that started in 2007. It originated from a partnership between the Brazilian Metallurgical, Materials, and Mining Society (ABM) and The Minerals, Metals and Materials Society (TMS). The seed was planted by Diran Apelian in his tenure as TMS President, whose vision of a North–South integration in the Americas led to a Memorandum of Understanding between TMS and ABM. Prior to that, preliminary discussions held between Robert Shull, Brajendra Mishra, Horacı́dio Leal, Sergio Neves Monteiro, and Marc Meyers led to the suggestion of a greater integration among materials societies in the Americas, through a new conference series. The First TMS-ABM International Materials Congress, held in 2010 in Rio de Janeiro, marked the beginning of a partnership that also included representatives from corresponding societies of Argentina, Canada, Chile, Colombia, Mexico and Peru. As a natural evolution, the Second Pan American Materials Congress was held in 2014 in São Paulo, in conjunction with ABM’s large annual conference. The Third Pan American Materials Congress, held in San Diego, included nine participating professional societies. It was co-located with the TMS 2017 Annual Meeting and Exhibition, with TMS in the role of host society. A program covering a variety of materials science topics was created based upon input from leading scientists and engineers representing eight countries and the nine international materials, metals, and minerals societies: