Narrow Results

Diamond films were synthesized on a Mo substrate using combustion flame. During the cooling process, most diamond films delaminated. From previous work it was shown that diamond films delaminated at a synthesis temperature less than 1300K (low temperature), and films did not delaminate at synthesis temperature more than 1400K (high temperature). In this study, to clarify the influences on the delamination of the interface, films synthesized at high temperature and low temperature were investigated by SEM and X-ray diffraction. The results show that in the case of low temperature, diamond films were synthesized on the Mo substrate, case of high temperature, Mo₂C and diamond phases were synthesized on the Mo substrate. Thermally induced interfacial stress occurs due to the thermal expansion mismatch between the synthesized film and the Mo substrate. The interfacial stress by high temperature and low temperature was determined as the cause of the delamination. Thus, the interfacial stress of each synthesized temperature was calculated by a finite element method. The results show that the interfacial stress in the film synthesized by high temperature was smaller than that by the low temperature. As the buffer phases prevent the delamination, synthesized films by high temperature will be useful as hardcoating layer for a metal surface.

The interlaminar peel strength of Al/AFRP (Aluminum alloy/Aramid Fiber Reinforced Plastic) hybrid composite is affected by the adhesive strength between the Al alloy layer and the aramid fiber layer. The study of the tensile strength and the T-peel strength of the Al/AFRP should be accomplished first. Therefore, this study focused on the effect of the resin mixture ratio as the Al/AFRP on the tensile strength and T-peel strength. In conclusions, the resin mixture ratio by equivalence ratio of 〈epoxy resin : curing agent〉 equal to 〈1:1〉 of Al/AFRP-I and the resin mixture ratio by equivalence ratio of 〈epoxy resin : curing agent : accelerator〉 equal to 〈1:1:0.2〉 of Al/AFRP-II showed the highest ultimate tensile strength. After the T-peel test, it is found that the T-peel strength of Al/AFRP-II is approximately 1.5 times higher than that of Al/AFRP-I. Reviewing the characteristics of the tensile and T-peel strengths, the resin mixture ratio 〈1:1:0.2〉 of Al/AFRP-II showed the highest tensile strength and T-peel strength.

The advanced piezoelectric ceramic composite actuator, which is called LIPCA (LIghtweight Piezoelectric Composite Actuator), replaced the Al foil and stainless steel in THUNDER with the FRP and the optimization of the laminate configuration was performed to maximize the stress transfer and the fiber bridging effect. This study evaluated the fatigue characteristics in LIPCA under the resonance frequency, and the changes of its interlaminar phase were also evaluated. Beside, the residual stress distribution was estimated. In conclusions, firstly, comparing with the fatigue life of LIPCA without the artificial delamination (intact LIPCA), the fatigue life of LIPCA embedded by the artificial delamination was decreased up to 50%. Secondly, the micro void growth and the coalescence of epoxy were actively made at the interlaminar phase subject to the large tensile stress. Finally, it was known that the harmonic configuration between the compressive residuals stress and the tensile one was made. The requirement of the performance displacement increment was satisfied.

The mechanical properties of materials such as elastic modulus, hardness, and fracture toughness, can be measured by nanoindentation. For a thin film coated on an elastic substrate, the cross-sectional nanoindentation technique can decrease the influence of plastic deformation around the nanoindenter apex on fracture toughness for interface delamination. Considering the effect of the elastic substrate, the theory of an elastic beam bonded to an elastic foundation is further developed to obtain the energy release rate of interfacial debonding. Explicit closed-form solutions are determined, and the influence of the substrate on the energy release rate is shown graphically.

We have tried to find out the critical factor governing the delamination in the pearlitic steel filaments. Steel filaments were fabricated depending on the carbon content from 0.72 to 1.02 wt.%. The delamination was identified by a torsion tester specially designed for thin-sized wires and scanning electron microscopy. The results showed that as the carbon content increased, the number of twists to fracture decreased, and the delamination only occurred in the filament with 1.02 wt.% C. In order to elucidate this behavior, the microstructure of the filaments was observed using advanced analysis techniques such as 3 dimensional atom probes tomography (3-DAPT).

Transparent polymer interlayer foils are widely used to increase the safety of glass applications, mainly in construction and automotive industry. In case one or more glass sheets in a laminate fracture, the remaining structural capacity (i.e. stiffness and strength) highly depends on the solicitation and mechanical properties of the interlayer. In such a post-breakage state, the interlayer is subjected to a complex combination of phenomena such as partial delamination, large strain deformation, strain hardening, rupture, etc. In partim 1, an analytical model is presented in order to describe the mechanical behavior of glass laminates in post-breakage state for a simple configuration. In addition, the theoretical model is compared to experimental results in part 2, which is published together with part 1.

The component of the hot gas path in gas turbines can survive to very high temperatures because they are protected by ceramic Thermal Barrier Coating (TBC); the failure of such coating can dramatically reduce the component life. A reliable assessment of the Coating integrity and/or an Incipient TBC Damage Detection can help both in optimizing the inspection intervals and in finding the appropriate remedial actions.

This study gives the TBC integrity; so other methods are required, like thermography to obtain indications of TBC delamination. Pulsed Thermography detects coating detachments and interface defects, with a large area of view but a spatial resolution of few mm. The mentioned techniques as a whole constitute a powerful tool for the life assessment of thermal barrier coating.

Carbon Fiber Reinforced Plastic (CFRP) composite laminates are widely used in aerospace and aircraft structural components due to their superior properties. However, they are regarded as difficult-to-cut materials because of bad surface quality and low productivity. Drilling is the most common hole making process for CFRP composite laminates and drilling induced delamination damage usually occurs severely at the exit side of drilling holes, which strongly deteriorate holes quality. In this work, the candle stick drill and multi-facet drill are employed to evaluate the machinability of drilling T700/LT-03A CFRP composite laminates in terms of thrust force, delamination, holes diameter and holes surface roughness. S/N ratio is used to characterize the thrust force while an ellipse-shaped delamination model is established to quantitatively analyze the delamination. The best combination of drilling parameters are determined by full consideration of S/N ratios of thrust force and the delamination. The results indicate that candle stick drill will induce the unexpected ellipse-shaped delamination even at its best drilling parameters of spindle speed of 10,000 rpm and feed rate of 0.004 mm/tooth. However, the multi-facet drill cutting at the relative lower feed rate of 0.004 mm/tooth and lower spindle speed of 6000 rpm can effectively prevent the delamination. Comprehensively, holes quality obtained by multi-facet drill is much more superior to those obtained by candle stick drill.

Coupling resonance mechanism of interfacial fatigue stratification of adhesive and/or welding butt joint symmetric and/or antisymmetric structures excited by horizontal shear waves are investigated by forced propagation analytical solutions derived by plane wave perturbation methods, integral transformation methods and global matrix methods. The influence of materials on the coupled resonance frequency is analyzed and discussed by the analytical methods. Coupling resonance of interface shear stress is a structure inherent property. Even a very small excitation amplitude at the coupling resonance frequency can result in interface shear delamination. The coupling resonance frequency decreases with the increase of interlayer thickness or shear wave velocity difference between substrate and interlayer. The results could be applied to layered and/or anti-layered structural design.

Intercalation of hydrogen phosphate (HPO₄) into Mg/Al-Layered Double Hydroxides (LDH) with DodecylBenzeneSulfonate (DBS) was investigated with regard to anion exchange, rehydration and a combination of delamination and anion exchange. HPO₄ could not be intercalated into the interlayer space of LDH with DBS when using either anion exchange or rehydration methods. However, HPO₄ was successfully intercalated into the Mg/Al-LDH using a combination of delamination and anion exchange methods.

High-temperature superconducting (HTS) film-substrate structures have great potential applications in magnets and superconducting cables that have great potential for high temperature superconducting wires in space solar power stations. The most important issue in the successful application of those structures is the delamination of interfaces. Therefore, in this paper, the delamination induced by electromagnetic force and temperature change in the superconducting film-substrate structure is studied. Energy release rates of delamination are given. It is found that thermal effect on the energy release rate is more significant when the electromagnetic force increases. If without electromagnetic force, as the crack length reaches at its critical value, the film will be buckling and the crack becomes a mixed crack. The closed-form solution of the energy release rate of the mixed crack is provided. On the other hand, when the crack length is smaller than its critical buckling length and the crack is the mode II crack. The influence of the stress intensity factor of the mode II crack is more significant for a thicker film. This suggests that the film should be designed to be thinner. This study is useful for engineers to design HTS film-substrate structures.

This research addresses limitations in current aviation composite assembly techniques, often constrained by certification challenges. To enhance bonded composite components, open holes are frequently introduced, leading to increased vulnerability to delamination, a prominent failure mode in composite laminates. This study focuses on observing the impact of open holes on the mode II behavior of composites under various distances and hole diameter conditions. Results illustrate distinct load–displacement curves influenced by hole size, with shorter distances accelerating crack propagation, evidenced by reduced elastic regions and lower load values. Analyzing specimen appearances and crack patterns highlights stress concentration at the hole, influencing initiation and propagation. In the absence of a hole, cracks exhibit a zig-zag pattern near the loading point, while with a hole, they concentrate around it. Elastic region length varies with the pre-crack-to-hole distance, indicating accelerated crack propagation in shorter distances. This study underscores the direct influence of hole size on load values, emphasizing its pivotal role in determining composite mechanical properties. This research provides valuable insights into hole characteristics’ interplay with delamination behavior in carbon fiber-reinforced composites, essential for optimizing aerospace component design and structural integrity.

This paper revolves around a newly introduced weak solvability concept for rate-independent systems, alternative to the notions of Energetic ($\mathrm{\text{E}}$) and Balanced Viscosity ($\mathrm{\text{BV}}$) solutions. Visco-Energetic ($\mathrm{\text{VE}}$) solutions have been recently obtained by passing to the time-continuous limit in a time-incremental scheme, akin to that for $\mathrm{\text{E}}$ solutions, but perturbed by a “viscous” correction term, as in the case of $\mathrm{\text{BV}}$ solutions. However, for VE solutions this viscous correction is tuned by a fixed parameter. The resulting solution notion turns out to describe a kind of evolution in between Energetic and BV evolution. In this paper we aim to investigate the application of $\mathrm{\text{VE}}$ solutions to nonsmooth rate-independent processes in solid mechanics such as damage and plasticity at finite strains. We also address the limit passage, in the $\mathrm{\text{VE}}$ formulation, from an adhesive contact to a brittle delamination system. The analysis of these applications reveals the wide applicability of this solution concept, in particular to processes for which $\mathrm{\text{BV}}$ solutions are not available, and confirms its intermediate character between the $\mathrm{\text{E}}$ and $\mathrm{\text{BV}}$ notions.

This paper is concerned with an abstract inf-sup problem generated by a bilinear Lagrangian and convex constraints. We study the conditions that guarantee no gap between the inf-sup and related sup-inf problems. The key assumption introduced in the paper generalizes the well-known Babuška–Brezzi condition. It is based on an inf-sup condition defined for convex cones in function spaces. We also apply a regularization method convenient for solving the inf-sup problem and derive a computable majorant of the critical (inf-sup) value, which can be used in a posteriori error analysis of numerical results. Results obtained for the abstract problem are applied to continuum mechanics. In particular, examples of limit load problems and similar ones arising in classical plasticity, gradient plasticity and delamination are introduced.

The CVD diamond film with favorable adhesion and relatively thinner thickness is essential facing for its application on drills for machining carbon fiber reinforced plastics (CFRP), with regard to either the tool lifetime or the machining quality. A 500-nm-thick CrN layer was deposited by the cathode arc technique on slight chemical etched WC–Co 6wt.% drill, and nano-crystalline diamond (NCD) is subsequently deposited by the hot filament chemical vapor deposition (HFCVD) technique. The same NCD film is also deposited on the drills pretreated only by the slight chemical etching or the CrN interlayer, which are adopted as comparisons in the present study. The nucleation and growth of diamond film and the cutting performance of the coated drills are systematically studied. The results show that the drill pretreated by the slight chemical etching and CrN interlayer can acquire highest nucleation density (ND) compared to the other pretreatment methods as it sufficiently prevents the Co diffusion. The diamond-coated drill with deep chemical etching was used for comparison to study the machining quality when drilling CFRP. During machining the CFRP, the failure mode of the diamond-coated drill is mainly the delamination and peeling off of the diamond film at areas with stress concentration, while the diamond-coated drill pretreated by slight chemical etching $+$ CrN interlayer can retard such failure. The exit hole quality of CRFP machined by drill pretreated with slight chemical etching $+$ CrN interlayer is better than that by drill pretreated with deep chemical etching, which is ascribed to the different cutting edges of the drills.

This research work focuses about fabrication and investigation on the influence of Titanium Carbide (TiC)-graphite particles reinforcement in wear behavior of Aluminium Matrix Composites (AMC). The stir casting technique was used to fabricate AMC reinforced with various weight percentage of TiC and graphite particles. Wear tests were conducted by using pin-on-disc wear testing machine. The hardness of the hybrid composites were recorded on the test specimen. The worn out surfaces of composites were analyzed using Scanning Electron Microscope (SEM). Results reveal that the presence of TiC and graphite particles improved the wear resistance. The wear of composite is primarily due to delamination and abrasion. The graphite particles serve as the solid lubricant on the wear of composite. The hardness of composite is improved with the decrease in weight percentage of graphite. SEM images reveal that the reinforcement particles in the matrix are homogeneously distributed. Also, worn-out surfaces of the composite were studied to observe wear track and wear mechanisms like plowing grooves, crack or cutting, and fragmentation.

In order to reduce the adverse effects on the environment and economy and to avoid health problems caused by the excessively used cutting lubrications, cryogenic machining is drawing more and more attention. In this work, a novel cryogenic machining approach was applied for drilling of carbon fiber-reinforced polymers (CFRPs). According to this approach, CFRP was dipped into the liquid nitrogen (LN₂) and it was machined within the cryogenic coolant directly. Various machinability characteristics on thrust force, delamination damage, tool wear, surface roughness, and topography were compared with those obtained with dry condition. This experimental study revealed that the novel method of machining with cryogenic dipping significantly reduced tool wear and surface roughness but increased thrust force. Overall results showed that the cryogenic machining approach in this study improved the machinability of CFRP.

The usages of carbon-fiber reinforced polymer (CFRP) in aerospace, defense, and structural fields are increasing due to their excellent properties. However, the materials design, forming of material, machine tool and processing conditions are major tasks in manufacturing industries. Particularly, the micro feature making on macro-components using vertical machining center is a challenge nowadays. In this work, two different drill bits, such as high-speed steel (HSS) and solid carbide (SC) micro-drill, were used to make drilling on CFRP material. The performance of drills was evaluated by obtaining minimum delamination and stress in drilling by varying cutting velocity (CV), feed rate (FR), and air pressure (AP). Regression equations were formed according to the measured quality performance characteristics. The linear weighted method-based combined objective function algorithm and Genetic Algorithm was followed to multi-objective optimization. Besides, the most influencing factors were also identified and discussed using analysis of variance. The results explained that the SC micro-drill performance was better than HSS micro-drill. Also, the CV has the most eminent parameters followed by FR.

In this work, the dry sliding wear behaviors of pure monolithic magnesium and magnesium–titanium dioxide (Mg–TiO₂) composites were studied using pin-on-disc tribometer against an oil-hardened nonshrinking die steel (OHNS) counter-disc with a normal load of 0.5–2kg and a sliding velocity of 1.5–2.5$\mathrm{\text{m}}\cdot {\mathrm{\text{s}}}^{-1}$ with the sliding distance and wear track diameter of 1500m and 90mm, respectively. The pin samples were characterized for their microstructural, nanomechanical and tribological properties such as wear rate, coefficient of friction and wear fractographs. Scanning electron microscopy (SEM) was used to analyze the worn-out surfaces of each pin sample in order to identify the different types of wear and wear mechanisms and the chemical constituents of each element were quantified by energy-dispersive spectroscopy. The influence of TiO₂ reinforcements on the nanomechanical behavior was studied by nanoindentation technique. As compared with pure Mg, the nanoindentation strengths of Mg–1.5TiO₂, Mg–2.5TiO₂ and Mg–5TiO₂ composites were found to increase by 11.9%, 22.2% and 35.8%, respectively, which was due to the addition of TiO₂ particles and also due to the good bonding at the interface of TiO₂ and magnesium particles. From the wear test results, a significant change in wear rate was observed with the change in normal load than that of sliding speed, whereas a significant change in coefficient of friction was noticed with the changes in both normal load and sliding velocity. The dominant wear mechanisms involved under the testing conditions were identified through plotting the contour maps and SEM fractographs. Also, from the fractographs it was noticed that delamination and plowing effect have been the significant wear mechanisms observed during low wear rate of samples, whereas melting, delamination and oxidation wear have been observed during high wear rate of pure Mg and its composites.

This study examined the effects of drilling parameters, tool geometry, and core material thickness (CMT) on thrust force and the delamination factor in the drilling of sandwich composites. Aluminum honeycomb (10 and 15mm in thickness) was used as the core material, with carbon fiber-reinforced polymer (CFRP) as the top and bottom surfaces. In the drilling experiments, three different cutting speeds (60, 78 and 100m/min) and two different feed rates (0.05 and 0.075mm/rev) were used. Drills having a diameter of 6.35mm and three different geometries (candlestick drills, twist drills and dagger drills) were used in the experiments. At the end of the experiments, thrust force was seen to increase with increased feed rate and CMT. Increased cutting speed generally decreased the thrust forces and the minimum thrust force was achieved with the 10 mm thick core material, 0.05mm/rev feed rate and 100m/min cutting speed using the dagger drill. The delamination factor at the entrance area was very low when drilling the sandwich composites and there was no significant difference based on drilling parameters, tool geometry, or CMT. Tool geometry was the main effective factor on exit delamination, and the highest delamination occurred with the use of the candlestick drill. Although increased feed rate increased delamination with all tools, with the dagger drill, increased cutting speed led to a severe increase. Delamination, tearing, and uncut fiber formation were observed when images of the exit areas of the drilled holes were examined.