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Solid-state batteries are generally considered to be safer than their liquid-state counterparts due to their decreased potential for fire or short circuiting. The fabrication of solid-state batteries relies on the application of stack crimping pressure that increases the interfacial surface contacts between electrolytes and the electrodes. However, excessive compressive crimping stresses (that occur in cell assembly) can give rise to cracking phenomena that can degrade battery performance and lead to thermal runaway or failure. It is, therefore, important to develop an understanding of failure mechanisms in solid-state Li-ion electrolytes. In this paper, we use a combination of in-situ optical microscopy and Digital Imaging Correlation (strain mapping) techniques to study compressive deformation and cracking phenomena in a novel solid-state Li-ion electrolyte. The stress states associated with the different stages of compressive deformation are also presented along with those due to charge–discharge cycles. The implications of the results are discussed for the material design of robust solid-state Li ion batteries.

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.

One route to a brighter global energy future may be through enhancing the efficiency and stability of perovskite solar cells (PSCs), which depends on the level of defects in the photoactive absorber and along the interfaces of the multilayered structure. Here, we use a combined experimental and theoretical approach to study the effects of pressure-induced compaction of microvoids and closure of cracks on the power conversion efficiency (PCEs) and stability of formamidinium-rich PSCs. A range of mechanical pressures was applied to the PSCs to reduce pre-existing grain-boundary voids and interfacial cracks within the devices. The PCEs of the PSCs increased from ~19.5% to ~ 23.5% for applied pressures between ~ (0 – 7) MPa. Unlaminated device stability increased by 33%, falling to 80% of initial PCE in 1800 hrs without compression, as compared to 2400 hrs with compression. The implications of this study are discussed in light of possible future manufacturing processes.

The interfacial robustness of perovskite solar cells (PSCs) is important due to the potential for failure resulting from applied loads or deformation in devices that are fabricated on rigid or flexible substrates, and/or residual stresses due to thermal expansion mismatch between layers. Since these can occur across any of the interfaces within typical hybrid organic–inorganic perovskite solar cells, we explore the mechanisms of interfacial fracture between the layered structures of model hybrid organic–inorganic perovskite solar cells. Brazil disk interfacial fracture specimens enable studies of the mode-mixity dependence of interfacial fracture toughness for each interface. The robustness of interfaces is studied across a range of mode mixities between pure mode I and pure mode II. A combination of optical and scanning electron microscopy further elucidates the underlying crack/microstructure interactions and fracture modes. These reveal crack-tip shielding due to crack bridging and microcracking, which were modeled using a zone shielding model to predict the mode-mixity dependence of the interfacial fracture toughness values. We discuss the implications for the development of hybrid organic–inorganic perovskite solar cells with robust interfaces for scalable deployment of photovoltaics.

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.

The corrosion behavior of 5-hydroxytryptophan (HTP), and clay particulate reinforced epoxy coatings is studied on a steel substrate that is used widely in pipelines and tanks. The corrosion behavior was studied in sodium chloride (3.5 wt. % NaCl) solutions that simulate potential seawater exposure at pH 3 and 7. X-ray diffraction (XRD) and Scanning Electron Microscopy (SEM) were used for microstructural characterization of the samples. The thermal stability was characterized using Thermogravimetric Analysis (TGA). The underlying corrosion reactions and reaction products were also elucidated via Fourier Transform Infrared Spectroscopy (FTIR). Electrochemical impedance spectroscopy (EIS) and in-situ observations of interfacial blisters were used to study the underlying degradation mechanisms. Electrochemical impedance spectroscopy revealed that for prolonged exposure of about 90 days and above, the composite materials exhibited better corrosion resistance at a pH of 3 as seen by the higher diameter of the Nyquist plot. Fewer corrosion products were observed on the scribed areas of the HTP samples in the scribe test in pH of 3 corroding environment. This signifies improved adhesion of the coatings in that environment for the HTP/epoxy coatings. The results obtained also show that a 1 mm blister size was observed in the pristine epoxy sample while no blisters were observed in the clay/epoxy and HTP/epoxy samples exposed at pH of 3. In the pH 7 environment, the EIS experiment revealed the presence of blisters with diameters in the range of 1–4 mm, after exposure for 90 days. The implications of the results are discussed for the corrosion protection of steel surfaces with composite coatings.

This paper explored the effects of pressure on contacts between layers of organic photovoltaic cells with poly (3-hexylthiophene):phenyl-C61-butyric acid methyl ester (P3HT:PCBM) as the active layer. The contacts between the layers are modeled using analytical concepts and finite element models. The potential effects of surface roughness and dust particles are modeled along with the effects of lamination pressure and adhesion energy. The results show that, increased pressure is associated with decreased void length or increased contact length. The contacts associated with the interfaces between the active layer and the hole/electron injection layer poly (3,4-ethylenedioxythiophene: poly styrenesulphonate (PEDOT.PSS) and Molybdenum trioxide (MoO3) are also compared. The implications of the results are discussed for the design of stamping/lamination processes for the fabrication of organic photovoltaic cells.

This paper examines the effects of cyclic bending on the deformation and failure of layers that are relevant to flexible organic solar cells (with Polyethylene Terephthalate (PET) substrates and Poly-3-hexylthiophene: [6,6]-phenyl-C61-butyric acid methyl ester (P3HT:PCBM) active layers). The deformation and cracking mechanisms are elucidated along with the stresses and crack driving forces associated with the bending of flexible organic solar cells. The changes in the optical properties (transmittance) of the individual layers and multilayers are then explored for layers/multilayers deformed to flexural strains and stresses that are computed using finite element models. The implications of the results are then discussed for the design of flexible organic solar cells.

This paper explores the effects of pressure on the interfacial surface contacts and the performance of organic solar cells. A combination of experimental techniques and analytical/computational models is used to study the evolving surface contacts profiles that occur when compliant, semi-rigid and rigid particles are interlocked between adjacent layers in model solar cell structures. The effects of layer surface roughness and interlocked (trapped) particles are also considered along with the effects of surface energy, adhesion energy, and pressure. The results show that increased interfacial contact lengths and decreased void lengths are associated with the application of increased pressure. Increased pressure also results in significant improvements in power conversion efficiency. These improvements in power conversion efficiency are associated with the closure up of micro- and nano-voids due to the application of pressure to layers produced via spin coating and thermal evaporation. The results suggest that pressure-induced contacts can be used to enhance the performance of organic solar cells.

This paper explores the extent to which pre-buckling of layers (in thin film multilayered structures) can be used to increase the flexibility of organic electronic devices. The deformation of wavy/buckle profiles, with a range of nano- and micro-scale wavelengths, is modeled using finite element simulations. The predictions from the models are then validated using experiments that involve the bending of layered structures that are relevant to flexible organic electronics. The introduction of pre-buckled profiles is shown to increase the range of deformation that is applied to model structures, prior to onset of significant stresses and strains. The implications of the work are discussed for the design of robust flexible organic solar cells.

In this paper, we present the results of a combined theoretical, computational and experimental study of failure mechanisms in model multilayers that are relevant to stretchable organic solar cells. The deformation of these structures is elucidated under monotonic loading that simulates possible stretching phenomena. The stress distributions within the layers and the possible interfacial crack driving forces are computed for model layered structures with well controlled thicknesses and elastic properties. The implications of the results are discussed for the improved design of stretchable organic solar cells with reliable optical properties.

This paper presents the results of an analytical and computational study of the contacts and interfacial fracture associated with the cold welding of Organic Light Emitting diodes (OLEDs). The effects of impurities (within the possible interfaces) are explored for contacts and interfacial fracture between layers that are relevant to model OLEDs. The models are used to study the effects of adhesion, pressure, thin film layer thickness and dust particle modulus (between the contacting surfaces) on contact profiles around impurities between cold-welded thin films. The lift-off stage of thin films (during cold welding) is then modeled as an interfacial fracture process. A combination of adhesion and interfacial fracture theories is used to provide new insights for the design of improved contact and interfacial separation during cold welding. The implications of the results are discussed for the design and fabrication of cold welded OLED structures.

This paper presents the results of experimental and theoretical/computational micro-wrinkles and buckling on the surfaces of stretchable poly-dimethylsiloxane (PDMS) coated with nano-scale Gold (Au) layers. The wrinkles and buckles are formed by the unloading of pre-stretched PDMS/Au structure after the evaporation of nano-scale Au layers. They are then characterized using atomic force microscopy and scanning electron microscopy. The critical stresses required for wrinkling and buckling are analyzed using analytical models. The possible interfacial cracking that can occur along with film buckling is also studied using finite element simulations of the interfacial crack growth. The implications of the results are discussed for potential applications of micro-wrinkles and micro-buckles in stretchable electronic structures and biomedical devices.