Critical Load For Delamination Research Articles

Low velocity impact and compression-after-impact response of hybrid pseudo-woven meso-architectured carbon/epoxy composite laminates manufactured via automated fiber placement

An experimental study is presented on the low velocity impact (LVI) and compression after impact (CAI) response of T800-SC carbon/epoxy laminates manufactured via automated fiber (AFP) placement manufacturing. Two hybrid laminate configurations consisting of unidirectional and pseudo-woven meso-architectured composite (MAC) sub-laminates are compared against a traditional quasi-isotropic control laminate. MAC sub-laminates are manufactured via a modified AFP process implementing tow skips. The MAC architecture is macroscopically heterogeneous with discontinuous and spatially varying fiber orientations both in-plane and through thickness resulting in multiple interfaces and an expanded design space. The laminates are tested under LVI energies of 15–55 J using a 25.4 mm diameter hemispherical projectile according to ASTM D7136. The results show similar load-displacement responses but significant difference in the LVI damage profiles and CAI strengths for the different configurations. The hybrid laminate configurations exhibit increased damage resistance with up to 37% higher critical delamination load and increased damage tolerance with 26% higher residual compressive strength after an impact of 55 J compared to control laminate.

Mechanical behavior of C/SiC T-section under pulling load

For the C/SiC T-section structures, fabrication defects such as pores and local delaminations can be easily formed in the intersection zone which significantly affect the load bearing capacity. In this work, the mechanical behavior of C/SiC T-section under pulling load was investigated, and especially the delamination behavior was studied by introducing the cohesive zone model into the finite element modeling. It was found that for C/SiC T-section under pulling load, the maximum critical delamination load was about 1075 N in the present work, and the interface delamination was the main failure mode. It was verified that the effective interfacial strength influenced the critical delamination load, and the strain energy release affected the delamination behavior of the T-section specimen. The failure mechanisms of C/SiC T-section under pulling load depend on the interface bonding states. When the interface is well bonded, the failure mechanisms mainly include matrix stripping, matrix fracture and fiber breakage. Otherwise, only the matrix stripping can be found at the interface of the C/SiC T-section specimen.

Mechanical properties and wear behavior of multi-layer diamond films deposited by hot-filament chemical vapor deposition

Diamond films were deposited on cobalt-cemented tungsten carbide (WC-Co) by Hot-Filament Chemical Vapor Deposition (HFCVD). The mechanical properties and wear behavior of single-layer and multi-layer diamond films were compared, based on the difference of diamond crystal formation and internal structure. Adhesive failure modes and critical loads, post-scratch tests, were identified according to the applied load, acoustic emission and friction force. For single-layer diamond films, the samples produced with lower CH4 concentration evidence columnar crystal diamond structure, which exhibit better adhesive properties. The samples produced with 5% CH4 exhibit the lowest hardness, however, due to their higher crystallinity and nucleation density, they exhibit higher toughness. The multi-layer diamond film with 300 nm alternate thickness per interlayer shows the highest critical delamination load (23.22 N). Concerning the multi-layer diamond films, the hardness and Young's modulus increases from 84.13 to 94.01 GPa and 788.65 to 936.26 GPa, respectively, with the alternate thickness change from 100 nm to 600 nm per layer, which indicates that thicker alternate layers lead to higher hardness and toughness. The wear behavior of the nano-crystalline (NCD) single-layer diamond films is potentially related to the less adequate adhesive abilities to the substrate material.

Substrate Bias Voltage Tailoring the Interfacial Chemistry of a-SiC x:H: A Surprising Improvement in Adhesion of a-C:H Thin Films Deposited on Ferrous Alloys Controlled by Oxygen.

Hydrogenated amorphous carbon thin films (a-C:H) have attracted much attention because of their surprising properties, including ultralow friction coefficients in specific conditions. Adhesion of a-C:H films on ferrous alloys is poor due to chemical and physical aspects, avoiding a widespread application of such a film. One possibility to overcome this drawback is depositing an interlayer-an intermediate thin film-between the carbon-based coating and the substrate to improve chemical interaction and adhesion. Based on this, interlayers play a key role on a-C:H thin-film adhesion through a better chemical network structure at the outermost layer of the a-SiC x:H interlayer, i.e., the a-C:H/a-SiC x:H interface. However, despite the latest important advances on the subject, the coating adhesion continues being a cumbersome problem since it depends on multifactorial causes. Thus, the purpose of this paper is to report a standard protocol leading to surprising good results based on the control of the interfacial chemical bonding by properly biasing the substrate (between 500 and 800 V) during the a-SiC x:H interlayer deposition at an appropriate low temperature, by using hexamethyldisiloxane as precursor. The interlayers and the outermost interfaces were analyzed by a comprehensive set of techniques, including X-ray photoelectron spectroscopy, glow discharge optical emission spectroscopy, and Fourier transform infrared spectroscopy. Nanoscratch tests, complemented by scanning electron microscopy and energy-dispersive X-ray spectroscopy, were used to evaluate the critical load for delamination to certify and quantify the adhesion improvement. This study was important to identify the chemical local bonding of the elements at the interface and its local environment, including the in-depth chemical composition profile of the coating. An important effect is that the oxygen content decreases on increasing substrate bias voltage, improving the adhesion of the film. This is due to the fact that energetic ion hitting the growing interlayer breaks Si-O and C-O bonds, augmenting the content of Si-C and C-C bonds at the outermost interface of the a-SiC x:H interlayer and enhancing the a-C:H coating adhesion. Moreover, the combination of high bias voltage (800 V) and low temperature (150 °C) during the a-SiC x:H interlayer deposition allows good adhesion of a-C:H thin films due to sputtering of light elements like oxygen. Therefore, an appropriated bias and temperature combination can open new pathways in a-C:H thin-film deposition at low temperatures. These results are particularly interesting for temperature-sensible metal alloys, where well-adhered a-C:H thin films are mandatory for tribological applications.

A comprehensive study on different silicon-containing interlayers for a-C:H adhesion on ferrous alloys

Silicon-containing interlayers can be used to promote adhesion of a-C:H thin films on ferrous alloys substrates. In contrast to chromium and titanium intermediate layers, which are often deposited by well-established technologies such as physical vapor deposition (PVD), the deposition of silicon interlayers is more compatible with plasma enhanced chemical vapor deposition (PECVD) techniques since most of the precursors are usually presented as liquids in stantard conditions. In this work, different silicon-containing interlayers were deposited on AISI 4140 steel using three different precursors in a PECVD chamber equipped with electrostatic confinement. The tribological behavior was correlated with the chemical structure of the interlayer. The critical load for delamination depends more strongly on Si/O and C/O ratios than on deposition temperature. In a general way, low oxygen content in the silicon-containing interlayer is leading to high adhesion. The best adhesion was achieved by using hexamethyldisiloxane as precursor when a critical load for delamination of 3.6N was observed.

Unveiling the Roles of Binder in the Mechanical Integrity of Electrodes for Lithium-Ion Batteries

In lithium-ion secondary batteries research, binders have received the least attention, although the electrochemical performance of Li-ion batteries such as specific capacity and cycle life cannot be achieved if the adhesion strengths between electrode particles and between electrode films and current collectors are insufficient to endure charge-discharge cycling. In this paper, the roles of binders in the mechanical integrity of electrodes for lithium-ion batteries were studied by coupled microscratch and digital image correlation (DIC) techniques. A microscratch based composite model was developed to decouple the carbon particle/particle cohesion strength from the electrode-film/copper-current-collector adhesion strength. The dependences of microscratch coefficient of friction and the critical delamination load on the PVDF binder content suggest that the strength of different interfaces is ranked as follows: Cu/PVDF < carbon-particle/PVDF < PVDF/PVDF. The particle/particle cohesion strength increases while electrode-film/current-collector adhesion strength decreases with increasing PVDF binder content (up to 20% of binder). The electrolyte soaking-and-drying process leads to an increase in particle/particle cohesion but a decrease in electrode-film/copper-current-collector adhesion. Finally, the methodology developed here can provide new guidelines for binder selection and electrode design and lay a constitutive foundation for modeling the mechanical properties and performance of the porous electrodes in lithium-ion batteries.

Characterization and Adhesion in Cu/Ru/SiO2/Si Multilayer Nano-scale Structure for Cu Metallization

In this study, we have characterized the microstructure, resistivity, and dynamic deformation behavior of Cu/Ru/SiO2 and Cu/SiO2 samples under scratch loading conditions. Cu/Ru/SiO2 samples showed higher elastic recovery and hardness when compared to the Cu/SiO2 samples. In the case of Cu/Ru/SiO2 samples, Ru acts as a glue layer between the Cu and the SiO2 substrate providing both strength and toughness against dynamic loading. Hence, the critical load for delamination is higher for Cu/Ru/SiO2 samples compared to Cu/SiO2 samples. Our results show that Cu/Ru/SiO2 thin films present significant potential to be used in Cu metallization.

RF-PACVD of water repellent and protective HMDSO coatings on bell metal surfaces: Correlation between discharge parameters and film properties

Hexamethyldisiloxane (HMDSO) films have been deposited on bell metal using radiofrequency plasma assisted chemical vapor deposition (RF-PACVD) technique. The protective performances of the HMDSO films and their water repellency have been investigated as a function of DC self-bias voltage on the substrates during deposition. Plasma potential measurements during film deposition process are carried out by self-compensated emissive probe. Optical emission spectroscopy (OES) analyses of the plasma during deposition reveal no significant change in the plasma composition within the DC self-bias voltage range of −40 V to −160 V that is used. Raman and X-ray photoelectron spectroscopy (XPS) studies are carried out for film chemistry analysis and indicate that the impinging ion energy on the substrates influences the physio-chemical properties of the HMDSO films. At critical ion energy of 113 qV (corresponding to DC self-bias voltage of −100 V), the deposited HMDSO film exhibits least defective Si–O–Si chemical structure and highest inorganic character and this contributes to its best corrosion resistance behavior. The hardness and elastic modulus of the films are found to be bias dependent and are 1.27 GPa and 5.36 GPa for films deposited at −100 V. The critical load for delamination is also bias dependent and is 11 mN for this film. The water repellency of the HMDSO films is observed to be dependent on the variation in surface roughness. The results of the investigations suggest that HMDSO films deposited by RF-PACVD can be used as protective coatings on bell metal surfaces.

Effect of Adhesion, Film Thickness, and Substrate Hardness on the Scratch Behavior of Poly(carbonate) Films

ABSTRACT The effect of adhesion, film thickness, and substrate hardness on the scratch behavior of poly(carbonate) (PC) films was investigated. Films of various thickness were prepared by spin-coating solutions of PC in chloroform onto glass, ferroplate, Al 1100, Al 6022, and Al 6111 substrates. Adhesion between the films and the substrates was controlled by pretreatment of the substrates and the thickness of the films was controlled by the concentration of the PC solutions. Adhesion of the films to the glass substrates was measured by a blister test. Scratch tests were performed using a custom-built, progressive-load scratch tester with interchangeable diamond indenters; the resulting scratches were observed by optical microscopy, atomic force microscopy (AFM), and environmental scanning electron microscopy (ESEM). The critical normal load (i.e., the smallest applied normal load for which delamination of the film from the substrate was observed) was used as a criterion to determine the scratch resistance of the films. It was found that better film/substrate adhesion resulted in a higher critical load for delamination. As film thickness increased, the critical load and, thus, scratch resistance also increased. Substrate hardness had a strong influence on the scratch behavior of the PC films. For a low-hardness substrate (i.e., Al 1100), the work from scratching was mainly consumed by deforming the substrate. In the case of substrates with intermediate hardness (i.e., Al 6022, Al 6111, and ferroplate), the substrates were more resistant to the stresses that were generated in the films; hence, the deformation of the substrates was less severe. A high-hardness substrate (i.e., glass) resisted the applied load and resulted in higher stress concentrations in the films and at the interface. Consequently, a rougher surface inside the scratch track was observed.

Microstructural characterization of Ti–TiN/CN x gradient-multilayered coatings

A good mechanical performance of carbon nitride (CN x )-based hard coatings grown onto steel components requires an optimal adhesion to the substrates. In the present work, the CN x films have been joined to the AISI M2 steel substrates through a Ti–TiN functionally gradient underlayer. Three types of Ti–TiN/CN x graded systems were deposited by means of magnetron sputtering technique in different growing conditions and the adhesion properties were evaluated by scratch tests. Chemical and structural characterization at the nanoscale for these systems were carried out by grazing incidence X-ray diffraction, transmission electron microscopy (TEM), energy dispersive X-ray analysis, energy filtered TEM and electron energy loss spectroscopy. This complete microcharacterization of the multilayered Ti–TiN/CN x systems coupled with the observed adhesion properties has allowed to identify relationships between the deposition conditions and the material chemistry and structure, in order to reach the desired coating performance. A gradual enrichment in nitrogen and nitride phases was detected from the metallic substrate to the CN x top layer affording higher critical load for delamination.

Electroless polyol synthesis and properties of nanostructured Ni xCo 100− x films

A non-aqueous, electroless, polyol process was used to deposit nanostructured Ni x Co 100− x films on Cu substrates by reducing nickel acetate and cobalt acetate in refluxing ethylene glycol at 194°C for 1 h. As-deposited films were characterized using X-ray diffraction (XRD), scanning electron microscopy (SEM), vibrating sample magnetometry (VSM), microhardness and microscratch tests. The films had a (1 1 1) texture and the average crystallite size increased with x from 15 to 64 nm. The films showed in-plane magnetization anisotropy. Saturation magnetization ( M s) increased with increasing Co concentration and reached 1421 emu/cm 3 for Co 100. The perpendicular coercivity ( H c⊥) was higher than that in-plane ( H c). The Ni 50Co 50 film had the highest H c⊥ and microhardness compared to other films of different compositions. The critical load for delamination increased with x and was independent of film thickness. In this polyol process film deposition on the substrate competed with undesirable powder precipitation in the solution. Lowering the reaction temperature did not favor film deposition. However, film deposition occurred when an electric field was applied during the reaction at temperature as low as 100°C. Precipitation of colloidal particles persisted at this low temperature in a different diol.

Quasi-impact damage initiation and growth of thick-section and toughened composite materials

Results are presented for a study of damage initiation and growth in thick-section and toughened continuous fiber-reinforced composites resulting from a spherical indenter/impactor. The proposed analytical/computational model consists of several sub-models. A three-dimensional mesh generator is used for generating initial meshes for laminated composites containing various matrix cracks and delaminations. A stress analysis is developed in the framework of finite deformation for calculating stresses and strains of the composites with and without internal damage. A robust contact analysis proposed for handling the contact condition of cracked interfaces for matrix cracks/delaminations induced during indentation loading. A failure analysis is developed for predicting the damage initiation and propagation. A fracture mechanics based, simplified criterion is proposed for predicting the critical load for delamination growth.The proposed model predicts that the damage of thick-section composites may be initiated from the layer right below the indenter due to the compressive load, or the interior shear matrix cracks due to transverse shear. This contradicts the conclusions for thin, brittle laminated composites, in which surface cracking is in general the initial damage mode. It is shown that the delamination induced by the shear cracks is dominated by fracture modes II and III for growth of thick-section composites due to indentation loading. It is also interesting to observe that complicated contact zone exists for different delaminations.

Initiation and Propagation of Delamination in a Centrally Notched Composite Laminate

Interlaminar stresses occur at the free edge and notch to cause composite laminates to delaminate. Actually, delamination is an important failure mode and affected, for example, by fiber orientation and stacking sequence as discussed. In analysis, our de veloped mathematical model yields the interlaminar edge stresses and singularities around the hole to predict the onset of delamination. Furthermore, our work mainly aims to inves tigate experimentally the initiation and propagation of delamination subjected to tension and cyclic tension-tension (T-T) tests in centrally notched T300/5208 graphite/epoxy com posite laminates, including four layups: (a) orthotropic [=±45]4s, [90/0] 4s and (b) quasi- isotropic [0/90/±45]2s, [90/0/±45]2s. Experimental result and observation associated with the obtained maximum stresses and the adopted failure criterion are in good agree ment with our predicted delamination onset. Other important findings are highlighted as follows. The failure mode of each layup recorded by X-ray radiograph can be closely cor related to the prediction of our model. The delamination growth rate has also been mea sured. An approximately linear relationship between delamination area and stiffness re duction for the centrally notched quasi-isotropic lammates is established. The critical load for delamination can be estimated by the Hashin-Rotem failure criterion satisfactorily. As a benefit of nondestructive testing, we finally find that the residual strength of the laminate first increases as applied cycles increase and then decreases during fatigue tests. However, residual stiffness always decreases monotonically with the increase of applied cycles.

Delamination of Graphite/Epoxy Laminate During Drilling Operation

Delamination due to drilling is one of the major concerns in machining a composite laminate. This paper employed NIKE2D finite element code to predict the critical load for delamination in drilling simulation. Good agreement is achieved with the approximation analytical solution and the finite element results for the case of the model using isotropic material property. A circular plate of quasi-isotropic graphite/epoxy laminate with and without an aluminum plate backing was investigated for drilling load-induced delamination. It is found that drilling force-caused delamination can be significantly increased as the uncut portion is beyond a quarter thickness of the entire laminate thickness with an aluminum backing plate. It is suggested that the drilling operation be controlled as the drill nears the exit plane.