Toughness Of Films Research Articles

Lanthanide ions-induced formation of hierarchical and transparent polysaccharide hybrid films

Nacre-like hybrid films based on N-succinyl chitosan (NSC), sodium alginate (SA) and lanthanide ions were fabricated via coordination interactions. In this work, the binary building blocks (NSC and SA) were self-assembled into aligned hydrogel films by coordination with lanthanide ions, and hierarchical NSC-SA hybrid films were obtained upon drying. Two species of lanthanide ions (Gd3+ and Yb3+) were used to fabricate the hierarchical NSC-SA hybrid films. The as-prepared NSC-SA hybrid films exhibit high tensile strength and stability. The tensile strength and toughness of as-prepared hybrid films reach 122.10MPa and 3.89MJm−3, respectively. Meanwhile, the well-aligned lamellar microstructures also exhibit a good light transmittance. The highest light transmittance reaches 92% for NSC-SA hybrid films at 760nm. This fabrication method for hierarchical NSC-SA hybrid films is innovative due to the utilization of rare earth coordination bonding, and can serve as the basic strategy for the construction of high-performance composites in the near future.

Nanostructured ZnO films on stainless steel are highly safe and effective for antimicrobial applications.

The safety and effectiveness of antimicrobial ZnO films must be established for general applications. In this study, the antimicrobial activity, skin irritation, elution behavior, and mechanical properties of nanostructured ZnO films on stainless steel were evaluated. ZnO nanoparticle (NP) and ZnO nanowall (NW) structures were prepared with different surface roughnesses, wettability, and concentrations using an RF magnetron sputtering system. The thicknesses of ZnO NP and ZnO NW were approximately 300 and 620nm, respectively, and ZnO NW had two diffraction directions of [0002] and [01-10] based on high-resolution transmission electron microscopy. The ZnO NW structure demonstrated 99.9% antimicrobial inhibition against Escherichia coli, Staphylococcus aureus, and Penicillium funiculosum, and no skin irritation was detected using experimental rabbits. Approximately 27.2±3.0μgL-1 Zn ions were eluted from the ZnO NW film at 100°C for 24h, which satisfies the WHO guidelines for drinking water quality. Furthermore, the Vickers hardness and fracture toughness of ZnO NW films on stainless steel were enhanced by 11 and 14% compared to those of the parent stainless steel. Based on these results, ZnO NW films on STS316L sheets are useful for household supplies, such as water pipes, faucets, and stainless steel containers.

Effects of oxidation on fracture toughness of submicrometer-thick copper films

Effects of oxidation on fracture toughness of submicrometer-thick copper films

Self-reinforced poly(lactic acid) nanocomposites of high toughness

Abstract Self-reinforced poly(lactic acid) (SR-PLA) nanocomposites have been developed for the first time by using electrospun PLA fibre mats as a starting material followed by hot-compaction. During hot-compaction, the temperature was set while hot-pressing time was varied from 10 to 60 s to optimize processing conditions. The resulting transparent SR-PLA nanocomposite films were characterized using differential scanning calorimetry (DSC), scanning electron microscopy (SEM), and tensile testing. SEM observations confirmed that SR-PLA nanocomposites can be successfully prepared under the right conditions with hot-pressing time significantly affecting the composite microstructure. DSC results revealed that all SR-PLA films had considerably higher crystallinity with more stable crystallites and also a higher glass transition temperature when compared to bulk isotropic PLA film. Furthermore, a substantial improvement in both strength and ductility of these SR-PLA nanocomposites was observed in tensile testing. Of particular interest was the notable increase in toughness of the SR-PLA nanocomposite films as a result of their unique microstructure and related failure mechanisms.

Higher order Cauchy–Born rule based multiscale cohesive zone model and prediction of fracture toughness of silicon thin films

In this work, we extend the multiscale cohesive zone model (MCZM) (Zeng and Li in Comput Methods Appl Mech Eng 199:547–556, 2010), in which interatomic potential is embedded into constitutive relation to express cohesive law in fracture process zone, to include the hierarchical Cauchy–Born rule in the process zone and to simulate three dimensional fracture in silicon thin films. The model has been applied to simulate fracture stress and fracture toughness of single-crystal silicon thin film by using the Tersoff potential. In this study, a new approach has been developed to capture inhomogeneous deformation inside the cohesive zone. For this purpose, we introduce higher order Cauchy–Born rules to construct constitutive relations for corresponding higher order process zone elements, and we introduce a sigmoidal function supported bubble mode in finite element shape function of those higher order cohesive zone elements to capture the nonlinear inhomogeneous deformation inside the cohesive zone elements. Benchmark tests with simple 3D models have confirmed that the present method can predict the fracture toughness of silicon thin films. Interestingly, this is accomplished without increasing of computational cost, because the present model does not require quadratic elements to represent heterogeneous deformation, which is the inherent weakness of the previous MCZM model. Quantitative comparisons with experimental results are performed by computing crack propagation in non-notched and initially notched silicon thin films, and it is found that our model can reproduce essential material properties, such as Young’s modulus, fracture stress, and fracture toughness of single-crystal silicon thin films.

Photodegradation characterization and heterogeneity evaluation of the exposed and unexposed faces of stabilized and unstabilized LDPE films

The impact of climatic ageing on the characteristics of both unexposed and exposed faces of unstabilized and stabilized LDPE films was investigated. The effects on chemical and mechanical properties and on the heterogeneity in the films properties were discussed. The exposure periods were 8 and 21months for the unstabilized and stabilized films, respectively. The ATR-FTIR spectra detected initial presence of vinylidene groups that disappeared after 4months of weathering for both faces of the unstabilized films and disappeared earlier for stabilized films. It identifies also a progressive evolution of other photooxidation products, i.e. vinyl and carbonyl groups. The stabilized film demonstrated much better mechanical stability. Considerable reduction in the tensile toughness of unstabilized film was observed. The unstabilized film became quite fragile after 6months of exposure to sunlight to the extent it cannot be tested, while the stabilized film was exposed up to 21months exhibiting much higher durability. The microhardness MH measurements show increasing trend with weathering time and the impact on the exposed face of the unstabilized film was more severe. The ageing resulted in heterogeneity in the films properties and the MH and ATR-FTIR techniques could be used to evaluate its level.

Small-scale fracture toughness of ceramic thin films: the effects of specimen geometry, ion beam notching and high temperature on chromium nitride toughness evaluation

For the implementation of thin ceramic hard coatings into intensive application environments, the fracture toughness is a particularly important material design parameter. Characterisation of the fracture toughness of small-scale specimens has been a topic of great debate, due to size effects, plasticity, residual stress effects and the influence of ion penetration from the sample fabrication process. In this work, several different small-scale fracture toughness geometries (single-beam cantilever, double-beam cantilever and micro-pillar splitting) were compared, fabricated from a thin physical vapour-deposited ceramic film using a focused ion beam source, and then the effect of the gallium-milled notch on mode I toughness quantification investigated. It was found that notching using a focused gallium source influences small-scale toughness measurements and can lead to an overestimation of the fracture toughness values for chromium nitride (CrN) thin films. The effects of gallium ion irradiation were further studied by performing the first small-scale high-temperature toughness measurements within the scanning electron microscope, with the consequence that annealing at high temperatures allows for diffusion of the gallium to grain boundaries promoting embrittlement in small-scale CrN samples. This work highlights the sensitivity of some materials to gallium ion penetration effects, and the profound effect that it can have on fracture toughness evaluation.

Influence of MWCNTs modified by silane coupling agent KH570 on the properties and structure of MWCNTs/PLA composite film

Composite films based on poly(lactic acid)(PLA) filled with modified multiwalled carbon nanotubes (MWCNTs) were prepared by casting/solvent evaporation technique and investigated for their properties and structures. MWCNTs were modified by coupling agent KH570 which can improve the dispersion of MWCNTs and then enhance the comprehensive properties of PLA. The influences of modified conditions, including the amounts of KH570, the reaction temperature and time, were analyzed. And also the structures and properties of composite films were characterized by X-ray diffraction (XRD), scanning electron microscopy (SEM), fourier transform infrared (FTIR) and thermogravimetric analysis (TG). The two components of the composite films, WMCNTs and PLA, had excellent compatibility. The addition of MWCNTs modified by coupling agents KH570 was beneficial for the crystallization of PLA, and the toughness of composite films was also improved. When the reaction temperature was 70 °C, reaction time was 6 h, and the amount of KH570 was 3 % respectively, the obtained composite films had the perfect comprehensive properties.

Indentation of Polytetrafluoroethylene (PTFE) Thin Film: Simulations by Using Continuum Damage Mechanics

ABSTRACTThin compliant films on relatively hard substrates have a wide range of applications. In this work, continuum damage mechanics is used to simulate indentation of a 10-μm-thick polytetrafluoroethylene (PTFE) film deposited on glass for different load levels by finite element analysis. The results, compared to experiments, are useful in investigating the mechanics of wear and friction of soft thin films. The material model is elastic–plastic before damage initiation and includes linear damage progression thereafter. The effects of ductile and shear damage criteria and two parameters pertinent to the damage model, the equivalent plastic strain for damage initiation and the bulk fracture toughness, on the indentation are investigated. It is shown that the shear damage model is more suitable to characterize the indentation of the PTFE thin film. The bulk fracture toughness has greater significance with regard to damage compared to equivalent plastic strain at the onset of damage initiation. Comparison of simulation and experimental results shows that bulk fracture toughness of the thin PTFE film is approximately 20 J/m2. This value is lower than that for the bulk PTFE, and the difference is attributed to the thin-film nature of the case considered here.

Solution-processable CF 3 -substituted ductile polyimides with low coefficients of thermal expansion as novel coating-type protective layers in flexible printed circuit boards

Abstract This work proposes practically useful novel coating-type cover layer materials. A copolyimide (PI) system derived from pyromellitic dianhydride (PMDA, 50 mol%), 3,3′,4,4′-biphenyltetracarboxylic dianhydride (s-BPDA, 50 mol%) with 2,2′-bis(trifluoromethyl)benzidine (TFMB) showed a low coefficient of thermal expansion (CTE) by thermal imidization. However, this system was not compatible to chemical imidization process because of gelation. A structural modification of this copolymer by 4,4′-(hexafluoroisopropylidene)dianiline (HFIDA) significantly improved the solubility, as a result, allowed for chemical imidization in a homogeneous state and the formation of a stable PI solution from less hygroscopic solvents such as triglyme (TriGL). The TriGL-cast PI film at an HFIDA content of 25 mol% displayed excellent combined properties; a low CTE (22.9 ppm K −1 ), a very high T g (327 °C), and a common level of tensile properties [modulus ( E ) = 3.6 GPa and the elongation at break ( e b max ) = 10.4%]. The PMDA(50);s-BPDA(50)/TFMB copolymer system was also modified with other ether-linked fluorinated diamines; i.e., 2-trifluoromethyl-4,4′-diaminodiphenylether (3FODA) and 4,4′-bis(4-amino-2-trifluoromethylphenoxy)biphenyl (6FBAPB). At a 3FODA content of 25 mol%, the NMP-cast PI film displayed the lowest CTE (20.7 ppm K −1 ) among the PIs examined in this work. The modification using 6FBAPB was most effective to enhance the solubility. Thus, the structural modifications of PMDA(50);s-BPDA(50)/TFMB copolymer by these fluorinated diamines (HFIDA, 3FODA, and 6FBAPB) were an effective way to obtain almost satisfying target properties except for a high level of e b . A mechanism was proposed for explaining why the effect of the CF 3 -substituted ether-linked diamines on the toughness improvement was not so prominent. The approach simultaneously using some CF 3 -free ether-linked monomers enabled us to significantly enhance the film toughness ( e b max > 50%) while maintaining low CTE characteristics and good solution-processability. Thus, some of the PI systems can be promising candidates as novel coating-type cover layer materials.

Transparent blown films from poly(lactide) and poly(ethylene-co-vinyl acetate) compounds: Structure and property

The application range of poly(lactide), PLA, films is limited due to the brittleness and notch-sensitivity. In this work, thin films with balanced properties were fabricated by melt blowing of PLA and poly(ethylene-co-vinyl acetate) (EVA) blends. The film thickness is dependent on the taken-up speed and reached to around 10 μm at the taken-up speed over 14 m/min. The presence of EVA not only significantly enhanced the tensile toughness and notch-resistance of the PLA films but also retained high transmittance. The films exhibited anisotropic mechanical performances which were correlated to the micro-morphology differences between the take-up direction (DD) and the transversal direction (TD) as characterized by atomic force microscope. In addition, the EVA with 80 wt% VA units showed better overall modification effect on the PLA films than the EVA with 60 wt% VA units. Superior mechanical properties of PLA/EVA (80/20) blends such as tensile strength of 50–60 MPa, elongation at break up to 230% and tear strength of 85 kN/m were achieved in the DD direction. Meanwhile, balanced properties were also achieved in TD direction. Moreover, a transmittance of around 90% was obtained for the PLA/EVA films which are comparable to neat PLA films. A high enough VA unit content is crucial for superior mechanical properties and high transparency.

High tensile strength of sputter-deposited ZrB2 ceramic thin films measured up to 1016 K

We report the results of tensile experiments on 900 nm sputter-deposited films of ZrB2, performed at temperatures ranging from ambient to 1016 K. The ZrB2 samples were tested using micromachined sample frames with integrated micro-heaters. Transmission electron microscopy shows that both as-deposited films and films heated above 1000 K consist of two distinct layers, an amorphous layer and a crystalline layer with a very fine columnar structure. The ZrB2 films have a room-temperature tensile strength in excess of 1.2 GPa, far exceeding the tensile strength of bulk ZrB2, but their stiffness is lower and decreases significantly with increasing temperature. The reduction in stiffness is attributed to the presence of the amorphous phase and the high density of transverse grain boundaries in the crystalline region. The fracture toughness of the ZrB2 films was measured by introducing pre-cracks in the tensile specimens with a focused ion beam, and was found to be 2.57 ± 0.03 MPa√m, similar to values reported for bulk ZrB2.

Physicochemical and antioxidant properties of biopolymer/candelilla wax emulsion films containing hop extract – A comparative study

Emulsion films based on different biopolymers: carboxymethyl cellulose (CMC), oxidized potato starch (OPS), soy protein isolate (SPI), gelatin (GEL) and containing different concentrations of ethanolic hop extract (EHE: 0, 0.1, 0.25, 0.50%) were obtained and evaluated in terms of microstructure, water affinity, optical, mechanical, and antioxidant properties. SEM analysis showed that EHE improved homogeneity of wax in the protein films. In contrast, EHE induced the increase in wax particle size in CMC films. With the exception of CMC films, the presence of EHE reduced the solubility of films (p < 0.05). Incorporation of EHE significantly increased the water vapor permeability (WVP) of the polysaccharide-based films while had no effect on the WVP of protein-based films. The increase in EHE addition level resulted in films with enhanced barrier properties against UV light. SPI films were characterized by the best UV-blocking properties. EHE decreased visible light transmission of the polysaccharide films, while an opposite trend was observed for SPI films. The derivatives of structural polymers (GEL and CMC) produced films with higher mechanical strength and stiffness compared with the plant storage polymers. EHE caused a significant reduction in toughness of GEL and CMC films but did not affect the mechanical strength of OPS and SPI films. As the content of EHE increased, the films showed an increase in ferric reducing antioxidant power, metal chelating power and antiradical activity. The films susceptible to solubilization (CMC and SPI) had higher release of EHE and, consequently, better antioxidant activity compared to water-swollen films (OPS and GEL).

Indentation stress-based models to predict fracture properties of brittle thin film on a ductile substrate

Abstract In the present work, nano-indentation experiments were performed on the surface of alumina film and diamond-like carbon (DLC) film on PEEK substrates using an axisymmetric indenter. After indentation, ring cracks were noticed in the film by scanning electron microscope. Stress analysis results indicated that radial tensile stress on the surface of the film outside the contact region of the indenter caused the ring crack. Then, two stress-based models were proposed to predict fracture stress and fracture toughness of brittle thin film on a ductile substrate based on the crack channeling criterion. The models were expressed regarding critical indentation load, ring crack radius, plastic zone radius, and film thickness. The stresses in film predicted by the present models were validated using axisymmetric finite element analysis. Finally, the models were utilized to evaluate fracture toughness of the alumina film and DLC film in experiments.

Uniform Deposition of Chemical Vapor Deposition Diamond Films on Slender Tungsten Wires

In the present study, high-quality chemical vapor deposition (CVD) micro-crystalline diamond (MCD) film was successfully deposited on the surface of the Φ0.5 mm×120 mm tungsten wire using a special designed graphitic jig for supporting the substrate and a two-step deposition procedure for guaranteeing the uniformity of as-deposited diamond film. It is proved that as-deposited film indeed presented much more uniform thickness than that obtained using a conventional jig described in the previous literature, and a very thick WC interlayer spontaneously formed between the substrate and the diamond film, which together with as-deposited MCD film have significant effects on mechanical properties of the wire. Generally speaking, the coated wire remains extremely high surface hardness of the MCD film and considerable toughness of the substrate, along with favorable film-substrate adhesion. It is recognized that these the coated tungsten wires have broad application prospects, but the technologies for depositing diamond films that are thick enough on even longer and thinner wires still need further investigation.

In situ characterization of fracture toughness and dynamics of nanocrystalline titanium nitride films

Abstract

Miniaturized fracture experiments to determine the toughness of individual films in a multilayer system

Recently, the miniaturization of devices in the field of microelectronics has become more and more important. This also implies an increased complexity of the devices, where multilayer thin film systems play a major role. The use of various material combinations leads to the development of residual stresses, potentially causing cracks. Therefore, to prevent failures a thorough understanding of material properties such as the fracture toughness at small scales is indispensable, as these may differ significantly from bulk values. In this study we use miniaturized fracture tests to investigate the fracture behaviour of Cu–W–Cu and W–Cu–W trilayer thin film systems, having a thickness of 500 nm per individual W or Cu layer. The films are subjected to differences in elastic properties and residual stress gradients that both influence the fracture behaviour and thus have to be included in all considerations. We demonstrate that for the W layers a valid J-integral can be evaluated. However, we find that the presented advanced treatment does not allow the extraction of valid fracture mechanical quantities for the Cu layers, pointing out the need to develop a more sophisticated approach for ductile materials.

Microstructure, hardness and toughness of boron carbide thin films deposited by pulse dc magnetron sputtering

Boron carbide thin films were deposited on (100) silicon substrates at ambient temperature via. pulse dc magnetron sputtering. Various frequency and duty cycles were applied to the hot-pressed B4C target in order to understand their influence on the structure and mechanical properties of the B4C films. X-ray Energy dispersive spectrum, Raman spectroscopy and Transmission electronic microscopy were used to characterize the composition and microstructure of the films. Nanoindenter was employed to measure the hardness and modulus. The film toughness was evaluated by a microindentation method. The results show that both pulse frequency and duty cycle significantly affect the B/C atomic ratio and then hardness and modulus in the boron carbide films. However, the amorphous structure of the films was maintained when the frequency and duty cycle changed. The maximum hardness of 29GPa and modulus of 247GPa combined with relative high toughness (3.3MPam1/2) were achieved under 50kHz frequency and 30% duty cycle. In addition, there was no evidence to prove that the graphite phase existed in the B4C films although exceeded C concentration was detected.

Characterization and mechanical properties investigation of TiN-Ag films onto Ti-6Al-4V

To investigate their effect on fretting fatigue (FF) resistance of a Ti-6Al-4V alloy, hard solid lubricating composite films of TiN with varying silver contents (TiN-Ag) were deposited on a Ti-6Al-4V alloy using ion-assisted magnetron sputtering. The surface morphology and structure were analyzed by atomic force microscopy, X-ray diffractometry, X-ray photoelectron spectroscopy, and transmission electron microscopy. The hardness, bonding strength, and toughness of films were tested using a micro-hardness tester, scratch tester, and a repeated press–press test system that was manufactured in-house, respectively. The FF resistance of TiN-Ag composite films was studied using self-developed devices. The results show that the FF resistance of a titanium alloy can be improved by TiN-Ag composite films, which were fabricated using hard TiN coating doped with soft Ag. The FF life of Ag0.5, Ag2, Ag5, Ag10 and Ag20 composite films is 2.41, 3.18, 3.20, 2.94 and 2.87 times as great as that of the titanium alloy, respectively. This is because the composite films have the better toughness, friction lubrication, and high bonding strength. When the atomic fraction of Ag changes from 2% to 5%, the FF resistance of the composite films shows the best performance. This is attributed to the surface integrity of the composite film is sufficiently fine to prevent the initiation and early propagation of FF cracks.

Soft and flexible electroactive materials for neuroprosthetic devices

Event Abstract Back to Event Soft and flexible electroactive materials for neuroprosthetic devices Josef Goding1, Rylie A. Green1 and Laura A. Poole-Warren1 1 University of New South Wales, Graduate School of Biomedical Engineering, Australia Since the inception of neuroprosthetic devices in the 1950’s with the development of cardiac pacemakers, metallic materials have been used to conduct and inject electrical charge in the body. Neuroprosthetic devices typically use platinum or gold electrodes to inject charge into the surrounding tissue[1]. These electrodes have several limitations including their high stiffness (contributes to chronic inflammatory response), low charge injection limits and their tendency to dissolve due to electrically initiated chemical reactions. Similarly, platinum-iridium and cobalt-chromium-molybdenum alloys are commonly used as electrode leads in devices such as cochlear implants and cardiac pacemakers. The poor flexural properties of these alloys can result in failure of the lead component. Additionally, due to the metal wires acting as antennae, these devices are often incompatible with MRI techniques. Conductive polymers (CPs) are a promising alternative to metallic materials for the conduction and delivery of therapeutic charge in the body. However, CPs are brittle and friable and have a limited number of compatible formation techniques[2]. In order to create a soft and flexible conductive material, this study investigated the use of the CP complex poly(3,4-ethylenedioxythiophene:polystyrenesulfonate (PEDOT:PSS) and polyurethane (PU) to fabricate conductive elastomers (CE). To fabricate the PU-PEDOT:PSS elastomer, various loadings of PEDOT:PSS were dispersed in a solution of PU dissolved in dimethylsulfoxide. The solution was cast and dried to produce a CE film. Cyclic voltammetry (CV) and electrochemical impedance spectroscopy (EIS) were used to assess the charge storage capacity (CSC) and impedance of the CE films. Tensile tests were conducted to determine ultimate tensile strength (UTS) and elongation at fracture. Increasing the weight percent of PEDOT in the CE films from 8 to 24 wt% corresponded with an increase in CSC from 33 mC.cm-2 to 224 mC.cm-2 (Fig. 1). EIS revealed that all CE films had stable impedances between 0.1 Hz and 10 kHz with 0° phase angle below 1 kHz. Increasing the PEDOT content from 8 to 24 wt% corresponded with a decrease in impedance from 1608 Ω.cm-1 to 175 Ω.cm-1 (equivalent to 0.6 mS.cm-1 and 5.7 mS.cm-1 respectively). Tensile testing of the CEs proved they are capable of significant extension with the 8 wt% PEDOT CE capable of 480% extension with an UTS of 9.1 MPa (Fig. 2). Increasing the PEDOT content to 24 wt% decreased the toughness of the CE film with UTS and elongation reduced to 1.6 MPa and 90% respectively. Dispersing PEDOT:PSS throughout a PU network resulted in a soft, flexible, electrically active elastomer. The resulting CE is capable of conducting and injecting electrical charge, with increasing PEDOT:PSS content corresponding with increased CSC, decreased impedance and toughness. CEs hold great potential for use as flexible electrode arrays and leads due to their ideal electrochemical and mechanical properties and MRI compatibility. Future studies will focus on improving the conductivity of the CE films via elecrochemical depostion of CP within CE films as well as investigating the materials compatibility with conventional elastomer formation techniques.