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Ductility of polymer-supported metal films is important for flexible electronic devices and it is strongly affected by the metal film, polymer substrate, and their interfacial properties. In this paper, the effect of interfacial adhesion and substrate thickness on the metal film ductility was investigated. Mechanical behavior of 500 nm-thick aluminum (Al) films deposited on polyethylene-terephthalate (PET) substrates with thickness of 12, 25, and 50 μm was studied by tensile testing with in-situ electrical resistance measurements and post-mortem scanning electron microscopy. In addition, plasma etching was applied to tailor the PET surface condition before Al film deposition. Subsequently, the Al/PET interfacial adhesion was quantitatively evaluated using the laser spallation approach. The tensile tests showed that plasma etching improved the ductility of the Al films, and that the apparent ductility of the Al film on the 50 μm-thick PET substrate was substantially lower than that on the 12 and 25 μm PET thickness. Laser spallation results revealed that the plasma etching increased the Al/PET interfacial adhesion. The influence of plasma etching and substrate thickness on the Al film ductility can be explained by the interface adhesion and shear lag theory. Plasma etching improves the interfacial adhesion by inducing both chemical and physical changes on the PET surface, and substrate thickness contributes to interface shear stress upon strain localization. The competing effect of the interfacial adhesion and the interfacial shear stress leads to a limiting substrate thickness for the desired ductility at a given tensile strain.

Among many dermal armors, fish scales have become a source of inspiration in the pursuit of “next-generation” structural materials. Although fish scales function in a hydrated environment, the role of water and intermolecular hydrogen bonding to their unique structural behavior has not been elucidated. Water molecules reside within and adjacent to the interpeptide locations of the collagen fibrils of the elasmodine and provide lubrication to the protein molecules during deformation. We evaluated the contributions of this lubrication and the intermolecular bonding to the mechanical behavior of elasmodine scales from the Black Carp (Mylopharyngodon piceus). Scales were exposed to polar solvents, followed by axial loading to failure and the deformation mechanisms were characterized via optical mechanics. Displacement of intermolecular water molecules by liquid polar solvents caused significant (p ≤ 0.05) increases in stiffness, strength and toughness of the scales. Removal of this lubrication decreased the capacity for non-linear deformation and toughness, which results from the increased resistance to fibril rotations and sliding caused by molecular friction. The intermolecular lubrication is a key component of the “protecto-flexibility” of scales and these natural armors as a system; it can serve as an important component of biomimetic-driven designs for flexible armor systems. Statement of Significance The natural armor of fish has become a topic of substantial scientific interest. Hydration is important to these materials as water molecules reside within the interpeptide locations of the collagen fibrils of the elasmodine and provide lubrication to the protein molecules during deformation. We explored the opportunity for tuning the mechanical behavior of scales as a model for next-generation engineering materials by adjusting the extent of hydrogen bonding with polar solvents and the corresponding interpeptide molecular lubrication. Removal of this lubrication decreased the capacity for non-linear deformation and toughness due to an increase in resistance to fibril rotations and sliding as imparted by molecular friction. We show that intermolecular lubrication is a key component of the “protecto-flexibility” of natural armors and it is an essential element of biomimetic approaches to develop flexible armor systems.

Electronic speckle pattern interferometry (ESPI), a well-established technique for micro-deformation measurement, can be used to determine both in-plane and out-of-plane displacement components. Although many works in ESPI have been reported for three-dimensional (3D) displacement measurement, few works have focused on the simultaneous measurement of 3D deformation fields. Here we present an ESPI system that consists of three sub-interferometers for simultaneous measurement of all three displacement components and in-plane strain fields. A 3CCD color camera, a specially designed shifting stage, and three lasers with optimal wavelengths are used in this system. The lasers and 3CCD camera provide independent interferograms with different color signals, while the shifting stage allows the sub-interferometers to achieve simultaneous phase shifting. The results of color separation and experimental measurement demonstrate the utility of the system.

We propose an adaptive filter method based on a deformable window shape to remove the noise of wrapped phase fringe patterns in electronic speckle pattern interferometry (ESPI). The filter kernel automatically adjusts its size, shape, and direction according to the direction and curvature of the phase fringe pattern. The direction of a phase fringe pattern is determined using a gradient-based method. Fringe curvature is estimated based on the calculated direction and fitted phase contours. Simulations were performed to evaluate the proposed method, and the results were compared with those of the 2-D windowed Fourier transform filtering (WFTF) algorithm and the medial filter technique. Simulated and experimental results show that the new approach can provide more effective de-noising for phase fringe patterns compared to the other two methods, using few parameters.

Fish scales serve as a dermal armor that provides protection from physical injury. Due to a number of outstanding properties, fish scales are inspiring new concepts for layered engineered materials and next-generation flexible armors. While past efforts have primarily focused on the structure and mechanical behavior of ontogenetic scales, the structure-property relationships of regenerated scales have received limited attention. In the present study, common carp (Cyprinus carpio) acquired from the wild were held live in an aquatic laboratory at 10° and 20°C. Ontogenetic scales were extracted from the fish for analysis, as well as regenerated scales after approximately 1 year of development and growth. Their microstructure was characterized using microscopy and Raman spectroscopy, and the mechanical properties were evaluated in uniaxial tension to failure under hydrated conditions. The strength, strain to fracture and toughness of the regenerated scales were significantly lower than those of ontogenetic scales from the same fish, regardless of the water temperature. Scales that regenerated at 20°C exhibited significantly higher strength, strain to fracture and toughness than those regenerated at 10°C. The regenerated scales exhibited a highly mineralized outer layer, but no distinct limiting layer or external elasmodine; they also possessed a significantly lower number of plies in the basal layer than in the ontogenetic scales. The results suggest that a mineralized layer develops preferentially during scale regeneration with the topology needed for protection, prior to the development of other qualities.

Through biological evolution, bivalve mollusks developed shells to improve the utilization of metabolic energy and provide protection against external threats. In addition to the mechanical optimization of the microstructure, the design of the macroscopic shape of a bivalve shell naturally becomes a potential approach to achieving the aforementioned purposes. While the functions of some features of mollusk shells have been studied, the role of the suture-serrate margins, a common morphology of bivalve shell edges, in the global mechanical behaviors of bivalve shells requires further exploration. Here, we present how the serrate margins contribute to the global mechanical properties of bivalve shells. The results of the compression tests employed on a typical bivalve, M. mercenaria, showed that the complete bivalve shells with suture-serrate margins perform better in terms of strength and work to fracture than those without the margins under the same conditions (dry and wet). The primary failure types observed during compression reveal that the failure mechanisms of valve shells are dependent on the suture-serrate margin morphology and water content. Using numerical simulations, the mechanical functions of the suture-serrate margins were demonstrated. Specifically, serrate margins provide mutual resistance by "locking" complementary valves to redistribute and eliminate stress concentrations around pre-existing defects, thereby enhancing the mechanostability and strength of the entire structure.

The compressive mechanical properties of open-cell hollow-sphere structures were experimentally and numerically investigated. The geometric model of the structure, through which the connected regions between spheres were perforated, was derived from the traditional metallic hollow-sphere structure (MHSS). For the experimental study, 3D printing technology was used to fabricate structures made of nylon in different arrangements, such as simple cubic (SC), body-centred cubic (BCC) and face-centred cubic (FCC). The experimental results validated the effectiveness of the finite element models for structures arranged in different packing patterns. Based on numerical simulations, parametric studies were conducted to investigate the influences of the geometrical and material parameters on the basic mechanical properties of the structure, including the elastic modulus, Poisson's ratio and initial yield stress. The results confirmed the significant impact of the structure's relative densities, which depend on the different geometrical parameters, such as the spheres’ spatial pattern, wall thickness and connection radius, on the mechanical properties of the structure. Additionally, the influence of the material parameters, such as Young's modulus and the yield stress, on the mechanical properties were also detected and validated.

A panoramic dual-directional shearography system is proposed to simultaneously determine out-of-plane deformation derivatives in two directions and globally inspect the object to be tested. A dichroic filter (DF), a 3CCD camera, and dual-wavelength light are used in the proposed shearography configuration. The dual-wavelength light coupled with the corresponding imaging sensors of the 3CCD camera provides independent color signals and shearograms. Through adjustment of the tilted stereo-angle of the DF, which offers a second wavelength-dependent measurement, an additional independent image-shearing can be introduced into the setup. The auxiliary bi-mirror surrounding the object helps to fully illuminate the object surface and capture it in a single shot. Theoretical analysis and experimental results demonstrated the utility of the system.

The time-averaged electronic speckle pattern interferometry (ESPI) is employed to measure the frequencies and mode shapes of thin, cantilevered plates with root-slit. The first 12 order linear resonance frequency and mode shape of an intact cantilevered plate is determined by using FEM calculation. The dynamic response of the intact specimen forced by a PZT actuator is measured and its super-harmonic resonance of forced response is investigated experimentally. The results show that the principal mode shape of super-harmonic vibration is similar to its natural modal. In contrast to linear forcing vibration, the threshold of force for super-harmonic resonance is much higher than that of the former. In addition, linear free response of four cantilevered root-slit plates with variation length of slit are analyzed by applying the FEM calculation, and their responses of forcing vibration were measured by using the ESPI method. The validity and accuracy of the numerical prediction are confirmed through experimental studies. The present work shows that the ESPI technique can provide whole-field and real-time measurement for vibration analysis and can also be employed for validation of the FEM calculation.

This Letter demonstrates a novel lateral shear interferometer system for simultaneous measurement of three-dimensional (3D) shape and thickness of transparent objects. Multi-frequency fringe patterns can be created by tilting mirrors at different inclination angles. With a single camera, the multi-frequency fringes are recorded in one image. The phase-shift of the fringes can be generated synchronously only by moving a plane-parallel plate along an in-plane parallel direction. According to the feature of transparent materials, the thickness and 3D shape can be reconstructed simultaneously based on the relationship between the in-plane displacement and their characteristics. The experiment was conducted on a thin transparent film subjected to a shearing force, which verifies the feasibility of the proposed system.