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Biomaterials are an important source of inspiration for the development of strong and tough materials. Many improved and optimized synthetic materials have been recently developed utilizing this bioinspiration concept. Using side-chain-to-side-chain polymerization of cyclic β-peptide rings, a novel class of nanomaterials was recently introduced with outstanding mechanical properties such as toughness values greater than natural silks. In this work, molecular dynamics is used to understand the mechanics of side-chain-to-side-chain polymerization of cyclic β-peptide rings. Unbiased steered molecular dynamics simulations are used to show the difference in the strength of polymerized and unpolymerized processing of similar cyclic rings. The simulations are performed both in aqueous and vacuum environments to capture the role of water on the mechanical properties of the cyclic peptides. Our results show that unpolymerized peptides behave like brittle material, whereas polymerized ones can withstand some stress after initial failure with large values of strain-to-failure. Finally, we have shown that the strength of cyclic peptides in water is higher than in a vacuum.

This paper presents the results of an experimental and computational study of the effects of laser-induced heating provided by magnetite nanocomposite structures that are being developed for the localized hyperthermic treatment of triple-negative breast cancer. Magnetite nanoparticle-reinforced polydimethylsiloxane (PDMS) nanocomposites were fabricated with weight percentages of 1%, 5%, and 10% magnetite nanoparticles. The nanocomposites were exposed to incident Near Infrared (NIR) laser beams with well-controlled powers. The laser-induced heating is explored in: (i) heating liquid media (deionized water and cell growth media [Leibovitz L15+]) to characterize the photothermal properties of the nanocomposites, (ii) in vitro experiments that explore the effects of localized heating on triple-negative breast cancer cells, and (iii) experiments in which the laser beams penetrate through chicken tissue to heat up nanocomposite samples embedded at different depths beneath the chicken skin. The resulting plasmonic laser-induced heating is explained using composite theories and heat transport models. The results show that the laser/nanocomposite interactions decrease the viability of triple-negative breast cancer cells (MDA-MB-231) at temperatures in the hyperthermia domain between 41 and 44°C. Laser irradiation did not cause any observed physical damage to the chicken tissue. The potential in vivo performance of the PDMS nanocomposites was also investigated using computational finite element models of the effects of laser/magnetite nanocomposite interactions on the temperatures and thermal doses experienced by tissues that surround the nanocomposite devices. The implications of the results are then discussed for the development of implantable nanocomposite devices for localized treatment of triple-negative breast cancer tissue via hyperthermia.

Lyophilization of protein solutions, such as silk fibroin (silk), produces porous scaffolds useful for tissue engineering (TE). The impact of modifying lyophilization primary drying parameters on scaffold properties has not yet been explored previously. In this work, changes to primary drying duration and temperature were investigated using 3%, 6%, 9%, and 12% (w/v) silk solutions, via protocols labeled as Long Hold, Slow Ramp, and Standard. The 9% and 12% scaffolds were not successfully fabricated using the Standard protocol, while the Long Hold and Slow Ramp protocols resulted in scaffolds from all silk solution concentrations. Scaffolds fabricated using the Long Hold protocol had higher Young's moduli, smaller pore Feret diameters, and faster degradation. To investigate the utility of the different lyophilized scaffolds for in vitro cell culturing, the HepaRG liver cell line was cultured in the 3% to 12% scaffolds fabricated using the Long Hold protocol. The HepaRG cells grown in 3% scaffolds initially had greater lipid accumulation and metabolic activity than the other groups, although these differences were no longer apparent by Day 28. The deoxyribonucleic acid content of the HepaRG cells grown in 3% scaffold group was also initially significantly higher than the other groups. Significant differences in gene expression by 9% scaffolded HepaRG cells (CK19, HNFα) were seen on Day 14 while significant differences by 12% scaffolded HepaRG cells (ALB, APOA4) were seen on Day 28. Overall, modifying the primary drying parameters and silk concentration resulted in lyophilized scaffolds with tunable properties useful for TE applications.

Complex concentrated alloys (CCAs) are structural and functional materials of the future with excellent mechanical, physical, and chemical properties. Due to the equiatomic compositions of these alloys, cost can hinder scalability. Thus, the development of CCA-based coatings is critical for low-cost applications. The application of cold spray technology to CCAs is in its infancy with emphasis on transition elements of the periodic table. Current CCA-based cold spray coating systems showed better adhesion, cohesion, and mechanical properties than conventional one-principal element-based alloys. Comprehensive mechanical behavior, microstructural evolution, deformation, and cracking of cold spray CC-based coatings on the same and different substrates are reviewed. Techniques such as analytical models, finite element analysis, and molecular dynamic simulations are reviewed. The implications of the core effects (high configurational entropy and enthalpy of mixing, sluggish diffusion, severe lattice distortion, and cocktail behavior) and interfacial nanoscale oxides on the structural integrity of cold spray CCA-based coatings are discussed. The mechanisms of adiabatic heating, jetting, and mechanical interlocking, characteristics of cold spray, and areas for future research are highlighted.

Stress fields emerging from the transfer of forces between cells within multicellular systems are increasingly being recognized as major determinants of cell fate. Current analytical and numerical models used for the calculation of stresses within cell monolayers assume homogeneous contractile and mechanical cellular properties; however, cell behavior varies by region within constrained tissues. Here, we show the impact of heterogeneous cell properties on resulting stress fields that guide cell phenotype and apoptosis. Using circular micropatterns, we measured biophysical metrics associated with cell mechanical stresses. We then computed cell-layer stress distributions using finite element contraction models and monolayer stress microscopy. In agreement with previous studies, cell spread area, alignment, and traction forces increase, whereas apoptotic activity decreases, from the center of cell layers to the edge. The distribution of these metrics clearly indicates low cell stress in central regions and high cell stress at the periphery of the patterns. However, the opposite trend is predicted by computational models when homogeneous contractile and mechanical properties are assumed. In our model, utilizing heterogeneous cell-layer contractility and elastic moduli values based on experimentally measured biophysical parameters, we calculate low cell stress in central areas and high anisotropic stresses in peripheral regions, consistent with the biometrics. These results clearly demonstrate that common assumptions of uniformity in cell contractility and stiffness break down in postconfluence confined multicellular systems. This work highlights the importance of incorporating regional variations in cell mechanical properties when estimating emergent stress fields from collective cell behavior.

This paper presents the results of a combined experimental and theoretical study of the interfacial and mechanical properties of epoxy/clay composites coatings on a mild steel substrate. This was studied using nano-indentation and Brazil Disk techniques to determine the Young’s moduli, hardness values and mode mixity characteristics of the composite coatings. The Young’s moduli of the reinforced composites comprising 1, 3, and 5 wt. % of montmorillonite clay particles are shown to improve, respectively, by about 23%, 58%, and 50% while the respective hardness values increased by about 46%, 80%, and 88%, relative to those of pristine epoxy. The measured mechanical properties have also shown to compare favorably with predictions from composite theories (rule-of-mixture and shear lag theories). The interfacial toughness between X65 steel and the epoxy/clay coatings increases with increasing mode mixity. This is associated with crack-tip shielding by crack deflection and crack bridging. The trends in the measured mode-mixity dependence of the interfacial fracture toughness values are consistent with predictions from the simplified zone, normal zone, and row models (at lower mode mixity). The insights from the observations and the measured crack profiles are incorporated into zone and row models for the estimation of crack-tip shielding. The implications of the results are discussed for the design of epoxy/clay composites with attractive combinations of mechanical properties.

This paper presents the results of an experimental study of the fatigue and fracture behavior of Bambusa Vulgaris-Schrad bamboo. Mechanisms of crack initiation and growth are elucidated under monotonic and cyclic compressive failure or flexural loading. The microscopic studies of fatigue and fracture explore the effects of fiber/crack/ply orientation on crack growth and toughening mechanisms in single-edge notched and double -edge notched fracture mechanics bend specimens, which are studied in the “crack-arrestor” and “crack-divider” orientations. The compressive fatigue behavior of Bambusa Vulgaris-Schrad bamboo is also investigated in smooth un-notched specimens. The resulting stress-life behavior is shown to occur in a regime in which the maximum stresses exceed the critical conditions for the onset of progressive fiber buckling and shear band formation. This results ultimately in the nucleation and propagation of interlaminar cracks and shear cracks across the Bambusa Vulgaris-Schrad structures. The implications of the results are discussed for the design of robust bamboo structures.

Recent advances in the design of structural composites often mimic natural microstructures. Specifically, the structure of abalone nacre with its high stiffness, tensile strength, and toughness is a source of inspiration from the process of evolution. The inspiration from nacre can lead to design of a new class of architected structural materials with superb mechanical properties. This work presents a combined experimental and computational study on a set of bioinspired architected composites created using a cement mortar cast with brick-and-mortar and auxetic polymer phases. The impact of this unit-cell polymer phase on the flexural and compressive strengths, resilience, and toughness is thoroughly studied as a function of architected geometry. All mechanical properties of the architected composite specimens are found to be greater than those of control samples due to prevention of localized deformation and failure, resulting in higher strength. The architected composites showed more layer shear sliding during fracture, whereas the control samples showed more diagonal shear failure. After initial cracking, the architected composites gradually deformed plastically due to interlocking elements and achieved high stresses and strains before failure. Results also show that composites with the architected polymer phase outperform control samples with equal volume fraction of a randomly oriented polymer fiber phase. Extensive computational studies of the proposed unit cells are also performed and the results suggest that the orientation of cells during loading is critical to achieve maximum performance of a cementitious composite. The implications of these results are immense for future development of high performing construction materials.

The ability for materials to self-heal or grow new material to replace damaged material is an easy task for Nature, but not so common in engineering. Current approaches implement crystal-producing bacteria within concrete materials. In this issue of Matter, Srubar and colleagues explore the use of a photosynthetic cyanobacterium embedded in a sand-hydrogel scaffold to produce a promising concrete-alternative.

This paper presents the results of an experimental and computational study of the adhesion of triptorelin-conjugated PEG-coated biosynthesized gold nanoparticles (GNP-PEG-TRP) to triple-negative breast cancer (TNBC) cells. The adhesion is studied at the nanoscale using a combination of atomic force microscopy (AFM) experiments and molecular dynamics (MD) simulations. The AFM measurements showed that the triptorelin-functionalized gold nanoparticles (GNP-TRP and GNP-PEG-TRP) have higher adhesion to triple-negative breast cancer cells (TNBC) than non-tumorigenic breast cells. The increased adhesion of GNP-TRP and GNP-PEG-TRP to TNBC is also attributed to the overexpression of LHRH receptors on the surfaces of both TNBC. Finally, the molecular dynamics model reveals insights into the effects of receptor density, molecular configuration, and receptor-ligand docking characteristics on the interactions of triptorelin-functionalized PEG-coated gold nanoparticles with TNBC. A three to nine-fold increase in the adhesion is predicted between triptorelin-functionalized PEG-coated gold nanoparticles and TNBC cells. The implications of the results are then discussed for the specific targeting of TNBC.

Creation of super-tough ceramics is one of the main goals of materials science. Bioinspired design is shown to be the most effective method to achieve this goal. Previous studies on the mechanical performance of biological multilayered materials such as nacre have shown that their outstanding mechanical properties are direct results of the small-scale features and optimized arrangement of the elements in their microstructure. Hence, the freeze casting technique has been recently introduced as a novel method to create a new class of bioinspired polymer/ceramic composites. However, the method is cumbersome and the mechanics that controls the overall performance of these composites is not well-known. In this study, the mechanical performance of bioinspired alumina/polydimethylsiloxane (Al2O3/PDMS) and alumina/polyurethane (Al2O3/PU) composite samples with lamellar structure are experimentally and analytically investigated. Bioinspired multilayered samples with micron-size layers are fabricated using the challenging freeze casting technique. Different parameters such as solution concentration, freezing rate, and sintering temperature affect the structure, and subsequently, the mechanical performance of these multilayered materials. Moreover, in order to fully understand the underlying toughening and deformation mechanisms, a micromechanics model of the mechanical response of lamellar composites is presented. The closed-form solutions for the displacements of the layers as a function of constituent properties are derived to calculate the mechanical response of lamellar structured composites such as elastic modulus, strength, and tensile toughness. The experimental results agree well with the proposed analytical models. Fracture mechanics tests are also used to study the Resistance-Curve (R- Curve) behavior of the samples. Furthermore, important toughening mechanisms in these samples are discussed and governing equations for fiber bridging and fiber pull-out in lamellar ceramic/polymer composites are presented. Finally, detailed material design relationships are derived to identify future directions in the design of next generation structural composites.

The excellent mechanical properties that biological materials possess are greatly influenced by the geometrical properties of their small scale constituents. Nacre , also known as Mother of Pearl, is an organic-inorganic composite material that makes up the inner layer of seashells . Nacre is observed for its impressive combination of stiffness, strength, and toughness which can be attributed to its waviness and the layering pattern of the brick and mortar structure of ceramic and protein that allows nacre to exhibit great mechanical energy and dissipate it over a large volume. In this study, the effect of this waviness on a model architected multilayered material system is analyzed numerically and experimentally in order to understand its effects on the stiffness, strength, and toughness of nacre. 3-D printed composites with auxetic and nacreous structure were created and tested in tensile boundary conditions. Finite element analysis was used to study the stress distribution and mechanical response of these composites. Results from the finite element models and the mechanical tests results show that increasing the tablet’s waviness increases the stiffness, however, there is an optimum value of tablet waviness for the highest strength and tensile toughness. Increasing waviness level can improve the elastic modulus by about 23%, strength by about 65% and toughness by about 42%. Using the proposed modeling approach, more detailed studies can be done on the toughening mechanisms of composite multilayered materials. These results can be used as a guide to design super-tough composites with multilayered structures.

An exceptional combination of mechanical properties such as high stiffness, high strength, and high toughness makes nacre one of the most remarkable natural materials. It has been shown that these outstanding properties arise from the multilayered brick-and-mortar structure of the nacre and the vital nanoscale features in its structure. Moreover, problem-solving strategies of naturally growing composites such as nacre give us a unique vision to design, optimize and fabricate simultaneously tough, stiff, and strong composites. It is widely known that nature’s biologically evolved, complex and effective functionally graded interfaces essentially enable the exceptional mechanical properties of biological composites. Particularly in nacre, the organic–inorganic interface referred hereto as interphase, in which the confined protein layer behaves stiffer and stronger in the proximity of the calcium carbonate minerals platelets, provides a key role in its toughness that is orders of magnitude higher than aragonite platelets as its main constituent. Hence, understanding the role of the interphase properties in the toughening mechanisms is paramount in the design and synthesis of high-performing bioinspired materials. In this study, a micromechanical model of the “Brick-Mortar” and “Brick-Bridge-Mortar” composites is presented focusing on the role of interphase properties on strengthening and toughening mechanisms. Shear-lag theory is employed on a simplified two-dimensional unit-cell of a multilayered composite. The computed closed-form solutions for the displacements as a function of constituent properties are used to calculate elastic modulus, strength, and work-of-fracture for a wide range of multilayered materials. Our results show that the properties of the soft phase in mineral bridges proximity can have a significant effect on the mechanical properties. The detailed relationships presented can help identify the future directions for advanced material design and development.

Concrete is the most widely used material in the world and is responsible for 8% of global carbon emissions. It is inherently brittle, and it requires frequent repair or replacement, which are expensive and generate large volumes of CO 2 . Current methods of repair by agents such as mortar and epoxies result in structures with reduced strength and resiliency due to material mismatch, therefore, a self-healing cement paste (concrete’s main matrix) is needed to overcome this problem. The leading self-healing mechanism is based on the use of bacteria and microbes, which are slow and have limited applications, as well as unknown health effects. Inspired by the extremely efficient process of CO 2 transfer in biological cells, this study introduces a method to develop a self-healing mechanism in a cementitious matrix using trace amounts of the enzyme Carbonic Anhydrase (CA). CA catalyzes the reaction between Ca 2 + ions and atmospheric CO 2 to create calcium carbonate crystals with similar thermomechanical properties as the cementitious matrix. The crystal growth rate using this method is orders of magnitude faster and more efficient than bacterial methods, resulting in the healing of large flaws on timescale orders of magnitude shorter. This method is capable of self-healing samples with millimeter-scale flaws within 24-hours and is significantly faster than all current methods that need a minimum of 28-days for strength recovery of microscale cracks. This inexpensive method is biologically safe, actively consumes CO 2 , and avoids using unhealthy reagents. It can be an efficient mechanism to repair and strengthen the existing concrete structures.

Bamboo is a natural composite abundantly available in the world, and is a source of inspiration for design of new construction materials and structural composites for many applications. The microstructure of this Functionally Graded Material (FGM) evolves through its thickness in response to wind-induced stresses that arise in the plant during its lifetime. This paper presents the results of an experimental study on the structure and toughening mechanisms in Moso culm bamboo. The hierarchical and multi-scale structure of bamboo and the distribution of micron scale fibers are revealed via optical microscopy. Four-point bend fracture experiments are performed where the applied crack-driving forces are computed as a function of crack length. This experimental data are incorporated within a finite element framework in order to understand the fracture and deformation mechanisms of bamboo, and compute the Resistance-curves ( R -curve)s. The resistance-curve behavior is shown to be dependent on the orientation of the fibers. In cases where the fibers are perpendicular to the crack growth toughening is observed to occur via crack bridging. Intermediate shielding levels are observed when toughening occurs by crack deflection for crack growth along the fiber orientation.

Forest-derived biomaterials can play an integral role in a sustainable and renewable future. Research across a range of disciplines is required to develop the knowledge necessary to overcome the challenges of incorporating more renewable forest resources in materials, chemicals, and fuels. We focus on wood specifically because in our view, better characterization of wood as a raw material and as a feedstock will lead to its increased utilization. We first give an overview of wood structure and chemical composition and then highlight current topics in forest products research, including (1) industrial chemicals, biofuels, and energy from woody materials; (2) wood-based activated carbon and carbon nanostructures; (3) development of improved wood protection treatments; (4) massive timber construction; (5) wood as a bioinspiring material; and (6) atomic simulations of wood polymers. We conclude with a discussion of the sustainability of wood as a renewable forest resource.

Current practices for repair of fractured stone architecture and monuments rely on drilling into the substrate and installing metal pins, providing component alignment and resisting shear and tensile stresses. Adhesives such as acrylic resin may reinforce the pins at the interface with the stone. This research studies failure modes in the repaired areas of the statue Adam (Tullio Lombardo c. 1490–95) to ensure the artwork's longevity. Six materials as pins were investigated to repair fractured Carrara marble specimens. Furthermore, the results of finite element simulations were correlated with experiments on pinned join repairs. The simulations and experiments concluded that fiberglass pins outperformed metal pins. The fiberglass pins provided maximum strength to withstand the static forces of the repaired sculpture, without damaging the substrate before pin failure. From the simulation results, a ranking of the pin materials quantified the overall efficiency of the system. The ratio of join displacements at the tension stress limit to the compression stress limit in Carrara marble indicates the join performance, where 1.0 represents equal strength in tension and compression. The fiberglass pin achieves a ratio of about 0.80, from which we conclude that sudden join failure may be prevented, a desirable trait for monumental conservation. Keywords: Finite element, Pin restoration, Marble, Structural, Historical, Conservation, Restoration

This paper presents the results of theoretical and experimental studies of the compressive deformation of bamboo (Bambusa Vulgaris-Schrad) in the middle section. The deformation mechanisms are elucidated via in-situ observations of deformation in specimens oriented for loading in directions that are either longitudinal or transverse. Compressive deformation is shown to result in progressive micro-buckling and kink band formation. The onset of micro-buckling is also shown to be well predicted by an Euler buckling model. The critical loads for failure in the transverse orientation are also shown to be consistent with the conditions for shear yielding in the plies with fibers that are oriented in an orthogonal direction to the loading axis.

Low temperature cracking is a prevalent mechanism of failure in hot mix asphalt (HMA) pavements. Prolonged cold temperatures can lead to premature cracking and subsequent failure of pavements. It has been previously shown that fibers as additives can improve the mechanical properties of asphalt mastic (asphalt binder and filler material passing the 75 μm sieve). However, the success of any effort to evaluate the low-temperature behavior of the fiber-reinforced asphalt mastic is based on the understanding of the fracture and toughening mechanisms. The objective of this study was to develop an asphalt mastic with enhanced resistance against cracking with the use of small amounts of fiber. Here, the effects of fiber length and content in the asphalt mastic were studied to create an asphalt mastic with enhanced fracture toughness. The Single Edge Notched Three-point Bending (SENB) test was performed at low temperatures to measure the strength and fracture toughness for polypropylene fiber-reinforced asphalt mastic. The major conclusions were that both fiber length and content improved the fracture properties of mastics significantly, and crack bridging and fiber pull-out were the two main toughening mechanisms in these materials.

Bamboo is a fast growing biomaterial that is of great interest as a rapidly renewable structural building material. As such, knowledge of the elastic properties is crucial to its use. Using non-contact, non-invasive Brillouin spectroscopy, we measure the entire elastic stiffness tensor and determine the complete set of elastic moduli of six species of bamboo fiber variants. The Young’s moduli, bulk modulus, shear moduli, and Poisson’s ratios are determined and shown to scale linearly with fiber density. These results provide the first order elastic properties of several fiber variants of bamboo which is crucial to a thorough understanding of how species variation yields specific elastic properties thereby enabling a complex understanding of the properties of this unique biomaterial.

The Surgeon General estimates that by 2020, half of all Americans could have weak bones due to bone loss. Osteoporosis causes more than 1.5 million fractures every year. Identifying effective interventions based on individual patient characteristics remains a major challenge. Proximal femur fractures are common and devastating events for individuals with osteoporosis. Since fracture is primarily a mechanical event, noninvasive predictions of fracture strength and location would be useful both for identifying at-risk individuals and evaluating treatment effects. However, bone fracture prediction is complicated due to the complex microstructure and nanostructure of bone. Bone is a highly heterogeneous material with rate-dependent mechanical behavior and large inter-individual variation. In this study, we designed two mechanical test procedures to understand the mechanical response of bone under impact and quasi-static load tests. The boundary conditions of the tests were designed in a way to simulate a fall to the side. The present study consists of three main parts: cadaver testing, quantitative image analysis, and finite element (FE) modeling. We obtained ten human femur bones and used high-resolution CT to quantify the microstructure and density of each sample. Specimen-specific FE models were created to evaluate the ability of various failure criteria to predict experimental fracture. Afterward, the samples were tested and their failure patterns were recorded. The fractured samples were rescanned to analyze the fractured surfaces. Our experimental results show that the loading necessary to fracture the femur samples is much higher in the impact tests. However, the toughening mechanisms are more pronounced in quasi-static tests. We found that FE model formulations were able to accurately predict femur stiffness and strength for quasi-static and impact conditions separately, but that no single formulation could account for the rate-dependent outcomes.

Nature employs lipids to construct nanostructured membranes that self-assemble in an aqueous environment to separate the cell interior from the exterior environment. Membrane composition changes among species and according to environmental conditions, which allows organisms to occupy a wide variety of different habitats. Lipid bilayers are phase-change materials that exhibit strong thermotropic and lyotropic phase behavior in an aqueous environment, which may also cause thermal rectification. Among different types of lipids, archaeal lipids are of great interest due to their ability to withstand extreme conditions. In this paper, nonequilibrium molecular dynamics simulations were employed to study the nanostructures and thermal properties of different archaeols and to investigate thermal rectification effects in asymmetric archaeal membranes. In particular, we are interested in understanding the role of bridged phytanyl chains and cyclopentane groups in controlling the phase transition temperature and heat flow across the membrane. Our results indicate that the bridged phytanyl chains decrease the molecular packing of lipids, whereas the existence of cyclopentane rings on the tail groups increases the molecular packing by enhancing the interactions between isoprenoid chains. We found that macrocyclic archaeols have the highest thermal conductivity, whereas macrocyclic archaeols with two cyclopentane rings have the lowest. The effect of the temperature on the variation of thermal conductivity was found to be progressive. Our results further indicate that small thermal rectification effects occur in asymmetric archaeol bilayer membranes at around 25 K temperature gradient. The calculated thermal rectification factor was around 0.09 which is in the range of rectification factor obtained experimentally for nanostructures such as carbon nanotubes (0.07). Such phenomena may be of biological significance and could also be optimized for use in various engineering applications.

Many biological materials display resilience rivaling engineered systems, but few have mechanisms that integrate failure with function. A new work by Espinosa et al. probes the peculiar behavior of the sea urchin’s teeth, which demonstrate utility beyond strength and toughness.

Current aims regarding environmental protection, like reduction of fossil fuel consumption and greenhouse gas emissions, require the development of new technologies. These new technologies enable the production of renewable energy, which is both cleaner and more abundant in comparison to using fossil fuels for energy production. This necessity encourages researchers to develop new ways to capture solar energy, and if possible, store it for later use. In this paper, the Pavement Solar Collector (PSC), and its use to extract low temperature thermal energy, is studied. Such a system, which harvests energy by flowing water through a heat exchanger embedded in the pavement structure, could have a significant energy output since pavement materials tend to absorb large amounts of solar radiation. The main objective of this paper is to develop a modeling framework for the PSC system and validate it with a self-instructed experiment. Such a model will allow for a detailed parametric study of the system to optimize the design, as well as an investigation on the effect of aging (e.g. decreasing solar absorptivity) on the performance of the system. A long-term energy output of the system that is currently lacking is calculated based on results of the study on weather parameters. This newly acquired data could be the start of a comprehensive data set on the performance of a PSC, which leads to a comprehensive feasibility study of the system.

This paper presents a review of high temperature ceramics research for aerospace applications. Following a brief historical perspective, the paper reviews the effort to toughen ceramics for high temperature structural applications. These include: efforts to toughen zirconia-based ceramics, aluminum oxide, silicon carbide, silicon nitride, molybdenum disilicide and zirconium diborides and carbon-based composites. The development of thermal protection systems is also reviewed within the context of thermal barrier coatings (TBCs) and thermal protection systems for space vehicles. The paper concludes with a final section in which the implications of the results are then discussed for the thermostructural applications of ceramics in aerospace structures.

An understanding of the properties of multifunctional materials is important for the design of devices for biomedical applications. In this paper, a combination of experiments and models was used to study the mechanical and hyperthermic properties of magnetic nanoparticles (MNP)-filled PDMS composites for biomedical applications. These are studied as a function of the weight of MNP, γ-Fe2O3. The results showed the effects on mechanical behavior, and specific losses in a magnetic field. The measured Young's moduli are in good agreement with the moduli predicted from the Bergström-Boybce model. Specific losses calculated from magnetic measurements are used to predict the thermal dose under in-vivo conditions. The implications of the results were discussed for potential applications in biomedical devices.

This paper is focused on understanding the role of combustive environment on thermal fatigue of Nextel™ 720/alumina CMCs. The role of pre-existing flaws in thermal monotonic and fatigue failure of the CMCs is also computationally and experimentally investigated. A notch (hole) was fabricated on the samples to study the effect of defects on the mechanical behavior of CMCs in combustion environment. Fatigue life in the combustion condition for notched samples was lower by an order of magnitude in comparison to the unnotched samples in combustion environment and notched samples in isothermal furnace results across the range of applied stress. The different fatigue performance is attributed to the thermal gradient stresses and increased rate of oxidation due to a high moisture level in the combustion rig test condition. The former will be further verified using finite element analysis and the latter from finite element analysis and microscopic analysis of the fracture surfaces.

Concrete is the most used material in the world. It is also one of the most versatile yet complex materials that humans have used for construction. However, an important weakness of concrete (cement-based composites) is its low tensile properties. Therefore, over the past 30 years many studies were focused on improving its tensile properties using a variety of physical and chemical methods. One of the most successful attempts is to use polymer fibers in the structure of concrete to obtain a composite with high tensile strength and ductility. The advantages of polymer fiber as reinforcing material in concrete, both with regard to reducing environmental pollution and the positive effects on a country's economy, are beyond dispute. However, a thorough understanding of the mechanical behavior of fiber-reinforced concrete requires a knowledge of fiber/matrix interfaces at the nanoscale. In this study, a combination of atomistic simulations and experimental techniques has been used to study the nanostructure of fiber/matrix interfaces. A new model for calcium-silicate-hydrate (C-S-H)/fiber interfaces is also proposed on the basis of scanning electron microscopy (SEM) and energy-dispersive X-ray spectroscopy (EDX) analyses. Finally, the adhesion energy between the C-S-H gel and three different polymeric fibers (poly(vinyl alcohol), nylon-6, and polypropylene) were numerically studied at the atomistic level because adhesion plays a key role in the design of ductile fiber-reinforced composites. The mechanisms of adhesion as a function of the nanostructure of fiber/matrix interfaces are further studied and discussed. It is observed that the functional group in the structure of polymer macromolecule affects the adhesion energy primarily by changing the C/S ratio of the C-S-H at the interface and by absorbing additional positive ions in the C-S-H structure.

Purpose: Multifunctional materials consisting of polymers and magnetic nanoparticles (MNPs) are highly sought after in the field of biomedical engineering. These materials offer new opportunities for the development of novel cancer treatment modalities that can increase the efficacy of cancer therapy. In this paper, a novel probe for multimodal cancer treatment is proposed and analyzed. The probe is essentially a cannula with two main parts: a distal heat generating tip made of a magnetic nanocomposite and a proximal insulated shaft. Methods: A description of the concept and functional operations of the probe is presented. In an effort to assess its feasibility, the authors evaluated the ability of probe tip (made of PMMA-Fe3O4 nanocomposite) to generate heat in biological tissue using alternating magnetic field (AMF) parameters (field strength and frequency) that are acceptable for human use. Heat generation by MNPs was determined using the linear response theory. The effects of Fe3O4 volume fraction on heat generation as well as treatment time on the thermal dose were studied. The finite element method model was tested for its validity using an analytical model. Results: Lesions were revealed to have an ellipsoidal shape and their sizes were affected by treatment time. However, their shapes remained unchanged. The comparison with the analytical model showed reasonably a good agreement to within 2%. Furthermore, the authors’ numerical predictions also showed reasonable agreement with the experimental results previously reported in the literature. Conclusions: The authors’ predictions demonstrate the feasibility of their novel probe to achieve reasonable lesion sizes, during hyperthermic or ablative heating using AMF parameters (field strength and frequency) that are acceptable for human use.

Successful monument repair projects have been completed by bringing together art conservators, engineers, and materials scientists. Conservators bring historical perspective and skill in repair. Engineers contribute numerical simulations and reinforced join designs. Materials scientists contribute specially designed adhesives and fracture mechanics-based material interactions. The repair of Adam (Tullio Lombardo c. 1490–95) challenged historical means and methods after a catastrophic accident. Prior restorations were limited by traditional techniques, most notably the use of invasive steel pins to repair fractures. This chapter details the design of an advanced fracture mechanics-based join repair using adhesives and pins, preserving the integrity and longevity of Adam. Included is the design of a protective adhesive to enhance the join’s mechanical performance. A pinning design is laid out, focusing on material selection, study of the stresses in the substrate and pin, and failure modes. Finally, recommendations are made for those seeking to undertake restorations.

Cement is one of the most consumed materials in the world. The cement industry is responsible for a large portion of global carbon dioxide emissions. Cement production and therefore carbon ...

Fiber Reinforced Polymer (FRP) sandwich panels have been commonly used in aerospace, marine and transportation applications. Their lightweight, high strength and superior durable characteristics make them a strong candidate for the construction industry. In specific applications, the core material between the FRP skins of the sandwich panels provides insulating properties that are beneficial for building applications. The panels used in this study are composed of Glass Fiber Reinforced Polymer (GFRP) skin layers, glass fiber insertions and a foam core. This paper presents the results of a computational and experimental study on the mechanical behavior of a 3-dimensional GFRP sandwich panel with through thickness fiber insertions. Samples of the GFRP skin and glass fiber insertions were cut out from larger panels and are tested to determine basic material properties of the components of the sandwich panels. The experimental results on the components were used to create a nonlinear finite element model that can predict the large-scale mechanical deformation of the sandwich panels. The model can predict force–displacement behavior of the panel accurately under a variety of experimental conditions. The finite element model was used to determine the bending capacity of sandwich panels of various span lengths to create load tables for design engineers. This model is further used to predict the mechanical performance and failure load of sandwich panels for specific load conditions. A parametric study was also performed to determine the correlation between the density and pattern of fiber insertions on panel behavior. The results show that increasing the density of fiber insertions makes the panel stiffer. An alternating pattern for the insertions also increased the overall panel stiffness. Varying the overall panel thickness between a minimum and a maximum thickness indicted that an optimal overall thickness could be established. The results of the parametric study agreed with the results in the literature.

In this paper, we studied a compliant tactile sensor with a spherical shell geometry. This bioinspired sensor has been successfully tested in actual robots whose behaviors are guided by tactile feedback. A model of the sensor was developed to study the contact response of the sensor to objects with different geometries. The sensor response is the estimation of both, normal and shear forces (3-D vector). The model was validated using experimental data and used to predict the behavior of sensors with different radii. This information allows us to design sensors with different sizes according to the requirements of a given robotic application.

This paper presents the results of a combined experimental and theoretical study of interfacial fracture in organic electronic structures. Interfacial fracture toughness is investigated as a function of mode mixity using Brazil disk specimens. The measured fracture toughness values are then compared with predictions determined from crack-tip shielding estimates and atomic force microscopy measurements of adhesion between layers that are relevant to organic electronic structures. The interfacial and layer fracture mechanics are elucidated before discussing the implications for the design of robust organic electronic structures.

This paper presents the results of an experimental study to understand the dominant mechanism in bond strength between dental resin agent and zirconia ceramic by investigating the effects of different surface treatments. Effects of two major mechanisms of chemical and micromechanical adhesion were evaluated on bond strength of zirconia to luting agent. Specimens of yttrium-oxide-partially-stabilized zirconia blocks were fabricated. Seven groups of specimens with different surface treatment were prepared. 1) zirconia specimens after airborne particle abrasion (SZ), 2) zirconia specimens after etching (ZH), 3) zirconia specimens after airborne particle abrasion and simultaneous etching (HSZ), 4) zirconia specimens coated with a layer of a Fluorapatite-Leucite glaze (GZ), 5) GZ specimens with additional acid etching (HGZ), 6) zirconia specimens coated with a layer of salt glaze (SGZ) and 7) SGZ specimens after etching with 2% HCl (HSGZ). Composite cylinders were bonded to airborne-particle-abraded surfaces of ZirkonZahn specimens with Panavia F2 resin luting agent. Failure modes were examined under 30× magnification and the effect of surface treatments was analyzed by scanning electron microscopy (SEM) and atomic force microscopy (AFM). SZ and HSZ groups had the highest and GZ and SGZ groups had the lowest mean shear bond strengths among all groups. Mean shear bond strengths were significantly decreased by applying a glaze layer on zirconia surfaces in GZ and SGZ groups. However, bond strengths were improved after etching process. Airborne particle abrasion resulted in higher shear bond strengths compared to etching treatment. Modes of failure varied among different groups. Finally, it is concluded that micromechanical adhesion was a more effective mechanism than chemical adhesion and airborne particle abrasion significantly increased mean shear bond strengths compared with another surface treatments.