Interface Debonding Energy Research Articles

Effect of Interface Properties on Tensile and Fatigue Behavior of 2D Woven SiC/SiC Fiber‐Reinforced Ceramic‐Matrix Composites

In this paper, the effect of the fiber/matrix interface properties on the tensile and fatigue behavior of 2D woven SiC/SiC ceramic‐matrix composites (CMCs) is investigated. The relationships between the interface parameters of the fiber/matrix interface debonding energy and interface frictional shear stress in the interface debonding region and the composite tensile and fatigue damage parameters of first matrix cracking stress, matrix cracking density, and fatigue hysteresis‐based damage parameters are established. The effects of the fiber/matrix interface properties on the first matrix cracking stress, matrix cracking evolution, first and complete interface debonding stress, fatigue hysteresis dissipated energy, hysteresis modulus, and hysteresis width are analyzed. The experimental first matrix cracking stress, matrix cracking evolution, and fatigue hysteresis loops of SiC/SiC composites are predicted using different interface properties.

Subsurface damage and material removal of Al–Si bilayers under high-speed grinding using molecular dynamics (MD) simulation

By performing three-dimensional molecular dynamics (MD) simulations, the effects of the tool radius, depth of cut and grinding speed are thoroughly studied in terms of the workpiece deformation, material removal, dislocation movement, atomic trajectory, grinding temperature and average grinding force. The strength of ductile/brittle (Al/Si) bilayers is largely enhanced, because the interface can hinder the passage of dislocations. The interface in brittle/ductile (Si/Al) bilayers contributes to its ductility by increasing the movability of dislocations when gliding on it. The brittle to ductile transition of bilayers, which strongly depends on the interface debond energy, has a key role in controlling the dislocation slipping mechanism. The investigation also reveals that a larger tool radius, higher grinding speed or deeper depth of cut results in more chipping volume and higher grinding temperature in both bilayers. At the same machining parameters, the above changes in brittle/ductile (Si/Al) bilayers are more apparent than that in ductile/brittle (Al/Si) bilayers, since Si is stiffer and has a higher yield strength than Al.

Effect of inter-layer toughness in ballistic protection systems on absorption of projectile energy

This paper concerns absorption of the kinetic energy of a projectile in multi-layer protection systems, with particular focus on the role of inter-layer bonding. Two-layer samples have been produced, composed of a 2 mm thick alumina front plate and a carbon fibre composite back plate with a thickness of about 0.8 mm. These were manufactured under two sets of conditions. The fracture energy of the inter-layer interface was measured for these two types of sample to be 170 and 620 J m−2. Such samples were subjected to impact by spherical projectiles of hardened steel, with a diameter of 8 mm and an impact speed of about 220 m s−1, corresponding to a kinetic energy of about 50 J. Samples composed of the alumina plate alone and of unbonded alumina and composite layers were also tested. It was found that significantly more projectile energy was absorbed by the strongly bonded samples, and that this difference was greater than could be explained solely in terms of the interfacial debonding energy. This is investigated by estimating the magnitudes of all of the identifiable sources of energy absorption, including that of plastic deformation of the projectile. It is concluded that strong inter-layer bonding can promote greater energy absorption in the composite back-plate.

Monte Carlo Simulation on the Matrix Failure Considering the Interfacial Debonding Energy

Considering the interfacial debonding energy at the fiber/matrix interface, an improved Monte Carlo simulation has been done on the matrix failure of the unidirectional ceramic matrix composites. Firstly, the debond length formula was given, then the stress/strain formula was also reviewed, and the matrix failure was simulated by the improved Monte Carlo model, the effect of the interfacial debonding stress on the matrix cracks evolution and the stress/strain curve was considered especially. Lastly, the result was compared to the experiment data. The result shows that the larger interfacial debonding energy at the fiber/matrix interface, the larger debond stress, the crack density increase more slowly, the mean crack density smaller, the final failure strength lower. The improved Monte Carlo simulation result is agreed well with the experiment data.

Effects of Interface Properties on Tensile Strength of Ceramic Matrix Composites

A definition of central crack damaged zone(CCDZ) is introduced based on tension experiments of Ceramic Matrix Composites(CMCs).The width of the CCDZ is defined to equal the debond length and the effect of interface toughness is neglected.When the CMCs rupture,the stress carried by the fibers can be estimated by the mean fiber stress within the CCDZ.Furthermore,the rule of mixtures is modified.Considering that the interface properties control the fracture mode,two kinds of models are presented respectively for brittle and ductile fracture strength.The stress concentration factor and interface debond energy release rate are introduced and discussed.It indicates that both the above factors result in decline of the tensile strength as they increase.The predictions of the given formulae are in good agreement with experimental data.

Experimentation on adhesion of epoxy

In a recent article (Sekulic and Curnier (2007) [1]), an original axisymmetric epoxy-stamp on glass-disc specimen, which exhibits stable debonding, was presented for identifying the adhesive properties between epoxy and glass, namely interface debonding energy ω , adhesion peak stress π n and debonding rupture gap γ n . In this article, the theoretical bases, experimental qualities and practical utilities of that specimen and experiment are discussed, demonstrated and illustrated. It is experimentally established that weak debonding stability (oscillatory secant increase of traction force with specimen elongation in the mean over debonding range) is determined by the slope of the epoxy-stamp radial profile, and that (strong) debonding stability (monotonous increase at each elongation along debonding range) is further determined by the glass-disc stiffness, hence by its thickness. It is demonstrated that a conical or parabolic or optimal blend epoxy-stamp on stiff-disc specimen can be reliably used to study adhesion of epoxy (and other glues) on plexiglas, glass, aluminium and steel (and many other materials).

The self-formatting barrier characteristics of Cu–Mg/SiO 2 and Cu–Ru/SiO 2 films for Cu interconnects

To substitute or to supplement diffusion barrier as reducing lateral dimension of interconnects, the alloying Mg and Ru to Cu was investigated as a self-formatting barrier in terms of their resistivity, adhesion, and barrier characteristics After annealing at 400 °C for 30 min, the resistivities of the Cu–0.7 at%Mg alloy and Cu–2.2 at%Ru alloy were 2.0 μΩ cm and 2.5 μΩ cm, respectively, which are comparable to that of Cu films. The adhesion was investigated by means of a sandwiched structure using the four point bending test. The interfacial debonding energy, which represents the adhesion, of Cu–Mg/SiO 2 was over 5.0 J/m 2, while those of the Cu–Ru/SiO 2 and Cu/SiO 2 interfaces were 2.2 J/m 2 and 2.4 J/m 2, respectively. The barrier characteristics of the alloy films were also investigated by the time-dependent dielectric breakdown test, using a metal–oxide–semiconductor structure, under bias-temperature stress. It was shown that the alloying of Mg made the lifetime seven times longer, as opposed to the alloying of Ru which made it shorter.

Electrical reliability and interfacial adhesion of Cu(Mg) thin films for interconnect process adaptability

The process adaptability of Cu(0.7–1.2 at.% Mg) alloy films for microelectronics interconnects was investigated by comparing their electrical properties, interfacial adhesion strength, time dependent dielectric breakdown (TDDB) reliabilities, and interfacial microstructure with those of pure Cu. The resistivity of the Cu(Mg) films decreased to ∼ 2.0 μΩ cm after annealing them in a vacuum at 350 °C for 10 min. The interfacial debonding energy measured by the four-point bending method was approximately 20.1 J/m 2 for Cu(Mg)/SiO 2 which is a factor of 2.3 larger than that of Cu/SiO 2 interfaces. The median time to failure of Cu(Mg)/SiO 2 in the TDDB test was much larger than that of pure Cu/SiO 2. The diffusion of Cu into the dielectric was found to be inhibited by the continuous very thin Mg–O layer formed at the Cu(Mg)/SiO 2 interface, which improves the interfacial adhesion, and ultimately leads to better electrical reliabilities.

Effect of Water Absorption on Interaction between Matrix Cracking and Fiber Bridging for Stress Corrosion Cracking of PMC

The effect of water on fiber bridging of polymer matrix composites (PMCs) has been studied for stress-corrosion cracking (SCC). The fiber bridging during crack propagation in the PMC was observed directly using a transparent polymer matrix. Specimens were immersed and weighed just before conducting the crack propagation test. The contribution of mechanical degradation caused by the water to the bridging was measured as a function of weight gain due to water absorption. The critical energy release rate of the matrix decreased with increase of the water absorption. The energy release rate of a bridged crack varied with the water absorption. To investigate the variation in the bridging mechanism under the water environment, we calculated the bridging stress the σt and the bridging contribution to crack propagation resistance ΔG based on a single-fiber bridging mechanism with the interfacial debonding length and the interfacial debonding energy. The debonding length was measured directly, and the debonding energy was obtained in a fragmentation test. The calculation showed that the increase in the interfacial debonding length influenced the fiber bridging mechanism.

The Coupled Thermoelastic Transversely Isotropic Bimaterial: Interface Crack Extension

A semi-infinite crack grows at a constant subcritical speed along the interface of rigidly bonded, dissimilar transversely isotropic, coupled thermoelastic half-spaces. Shear and normal loads that move on the crack faces drive the process. A dynamic steady state of plane strain is considered. Robust asymptotic full-field solutions for the related problem of translating interface disturbances are first obtained. These lead to coupled singular integral equations for the crack problem that are solved analytically. Expressions for the crack opening components and discontinuity in temperature between crack faces, the traction and temperature change ahead of the crack, and debonding energy rate are presented. These show that the critical crack speed is the minimum of the two Rayleigh speeds and, if it exists, the Stoneley speed. The case of zinc bonded to a thermally inert rigid solid is examined, and calculations for interface temperature change and debonding energy rate given. Apart from any fracture criterion, these parameters show sensitivity to crack speed and to the extent which compressive crack face loading dominates shear loading. Indeed, interface temperature change may decrease in magnitude with crack speed when shear loading dominates.

Self-assembled subnanolayers as interfacial adhesion enhancers and diffusion barriers for integrated circuits

Preserving the structural and functional integrity of interfaces and inhibiting deleterious chemical interactions are critical for realizing devices with sub-50 nm thin films and nanoscale units. Here, we demonstrate that ∼0.7-nm-thick self-assembled monolayers (SAMs) comprising mercapto-propyl-tri-methoxy-silane (MPTMS) molecules enhance adhesion and inhibit Cu diffusion at Cu/SiO2 structures used in device metallization. Cu/SAM/SiO2/Si(001) structures show three times higher interface debond energy compared to Cu/SiO2 interfaces due to a strong chemical interaction between Cu and S termini of the MPTMS SAMs. This interaction immobilizes Cu at the Cu/SAM interface and results in a factor-of-4 increase in Cu-diffusion-induced failure times compared with that for structures without SAMs.

Microstructures of ceramic composites with glass–ceramic matrices reinforced by SiC-based fibres

A lot of studies have been carried out on the fibre/matrix interfaces in glass–ceramic matrix composites reinforced by SiC based fibres. Chemical and structural analyses at the nanometer scale have shown that the fibre/matrix interface has a very complex structure consisting of several sublayers. The most important point is the existence of a thin carbon layer which is often found textured close to the fibre. This carbon layer acts as a mechanical fuse with a low or extremely low interfacial debonding energy. The mechanism responsible of the carbon formation and of the complex interfacial microstructure is still mater of controversy. This review will be focused on the microstructure of the interfacial region and on the different techniques which have been used to obtain chemical and microstructural parameters of the fibre/matrix interfaces in a large variety of glass–ceramic composites. The approaches concerning the SiC/BN dual-coated Nicalon SiC fibre-reinforced BMAS matrix composites will be described as well as the thermomechanical properties of this class of glass–ceramic composites and future research.

Devising a method to measure film adhesion through modeling

A method for measuring film adhesion is devised. It consists of a series of patterned film strips with different widths on a substrate, such that the driving force for each strip to debond increases as strip width increases when the system is subjected to residual and/or applied stresses. In this case, only those strips with sufficient driving force debond while the others remain attached to the substrate. Hence, qualitative comparison of the interface debond energy can be obtained by comparing the strip width below which debonding no longer occurs. By calculating the driving force for each strip to debond, the interface debond energy can be quantitatively determined.

Observations of Fiber Fracture and Interfacial Debonding Phenomena Using the Fragmentation Test in Single Fiber Composites

Fiber-reinforced polymer composites are being studied for many applications because of their potential for outstanding mechanical properties. To be used in new applications, composites have to be more fully understood. The fiber, the matrix, and the fiber/matrix interface are the building blocks that need study. This research has concentrated on the interface where debonds, or damage need to be studied more thoroughly. The experimental work here focused on the fragmentation test. The specimens used were AS4-carbon/Epoxy and E-glass/Epoxy composites. The fragmentation process was continuously monitored with careful attention to debonding at each break and debonding growth at higher strain as a function of applied tensile strain. Photoelastic birefringence patterns in the specimen were observed in more detail than ever to accurately monitor interfacial debonding and damage. The fiber fracture and the debonding length between the fiber and the matrix were measured only by visual observation using the photoelastic patterns rather than the Laser Raman Spectroscopy (LRS) which has usually been used in measuring interfacial debonding length or damage. This visual measurement technique provides the much simpler and more precise method than traditional LRS in measuring the fiber fracture and the interfacial damage in fiber-embedded composites. From the experimental data of fiber breaks and interfacial debond length, the interfacial toughness between the fiber and the matrix was analyzed for each composite system using the energy method. The interfacial debond energy, Γd, of AS4-Carbon/Epoxy was 220 J/m2 and 130 J/m2 for instantaneous debond and whole debond, respectively. For E-glass/Epoxy, Γd was obtained as 105 J/m2 and 98 J/m2 for instantaneous debond and whole debond, respectively.

A technique for the determination of interfacial properties from debond length measurement

Fiber-matrix interfacial debonding is observed and the debond length is directly measured during flexure tests performed on transparent SiC fiber-reinforced borosilicate glass composites. The relationship among the debond length, applied stress, and interfacial properties is investigated both experimentally and theoretically. A new technique based on debond length measurement is introduced for measuring fiber-matrix interfacial properties such as interfacial shear strength, frictional shear stress, and interfacial debond energy. Analytical models are employed for the new technique to interpret the experimental data. Fiber pushout technique is also employed to measure the interfacial properties independently. It is shown that these two different techniques of debond length measurement and fiber pushout test for measuring the interfacial properties can provide comparable results.

Prediction of overall tension behavior of short fiber-reinforced composites

The bridging stress of fibers along the crack surface plays an important role in analyzing the tension behavior of short or long fiber-reinforced composites. This paper uses the inclusion theory to obtain the expression of bridging stress for short fiber reinforced composite (SFRC) . A simplified model with periodically distributed fibers is proposed to estimate the average fiber spacings. The total fracture resistance is calculated as an energy summation including interface debonding energy dissipation, frictional sliding work between fibers and matrix, strain energy increment of fibers and matrix. The bend over point (BOP) stress is calculated by this fracture resistance. The necessary conditions of the fibers and matrix for the multiple cracking in SFRCs are discussed and the expression of ultimate external stress is derived. The critical fiber volume fraction for the strain hardening response is determined by an iteration method. In the meanwhile, the average spacing between two short fibers is proposed by a periodical distribution assumption. The theoretical prediction is compared with experimental data.

Interfacial shear debonding problems in fiber-reinforced ceramic composites

Toughening of fiber-reinforced ceramic composites by fiber pullout relies on mode II debonding at the fiber/matrix interface. This mode II debonding has been analyzed using the strength-based and the energy-based criteria, in which the interfacial shear strength and the interface debond energy are respectively adopted to characterize the debonding behavior. Using the concept of Griffith theory, an effective circumferential defect at the interface is defined to account for the stress intensity due to the presence of the fiber in the matrix and the fiber-pullout geometry. This effective circumferential defect is then used to derive the relation between the interfacial shear strength and the interface debond energy. Also, the condition of interfacial debonding vs fiber fracture for a bridging fiber behind the crack tip is established using the energy-based criterion.

Toughness of the fiber/matrix interface in nylon-6/glass fiber composites

The aim of the present study is to investigate the effects of the temperature and fiber surface finishing on the interfacial fracture toughness of nylon-6/E-glass fibers composites. The fracture toughness evaluation is based on a new method, recently proposed by the authors, which yields the strain energy release rate associated with the fiber/matrix interfacial debonding, G arrest , as a combination of a finite element analysis and experimental measurements on embedded single fiber microcomposites. For the unsized E-glass fibers an interface toughness of 165 Jm −2 has been found, while for the polyamide and epoxy compatible sized E-glass fibers higher interfacial debonding energy values of about 340 Jm −2 have been measured. Both sized and unsized E-glass fiber microcomposites showed a strong decrease of the interfacial toughness as the temperature increased.

A new model for the energy release rate of fibre/matrix interfacial fracture

On the basis of the well-known shear-lag analysis of fibre/matrix interface stresses and the assumption of identical axial strains in the fibre and matrix, a new model for predicting the energy release rate of interfacial fracture of the fibre pull-out test model is attempted. The expressions for stresses in the fibre, matrix and interface are derived. The formula for interfacial debonding energy release rate is given. Numerical calculations are conducted and the results obtained are compared with those of the existing models.

Microstructural Evolution and Mechanical Properties of Si3N4 with Yb2O3 as a Sintering Additive

Ytterbium oxide (Yb2O3) was used as a sintering aid to enhance the mechanical properties of silicon nitride (Si3N4) ceramics. The amount of Yb2O3 had significant effects on microstructural evolution and the composition of secondary phases at the grain boundary. When the Yb2O3 added was less than 8 wt%, small homogeneous grains were formed. At the grain boundary, crystalline Yb2Si2O7 was formed along with a glassy phase. As the amounts of Yb2O3 were increased to higher than 8 wt%, large elongated grains were developed in the fine matrix. In those cases, the grain boundary crystalline phase was changed from Yb2Si2O7 to Yb4Si2O7N2. Mechanical properties were influenced by these changes in microstructure and grain boundary phase. The fracture toughness increased with the Yb2O3 content up to 8 wt% and decreased slightly thereafter. The increase in fracture toughness was apparently due to the formation of the large elongated grains. When more than 8 wt% of Yb2O3 was added, interfacial debonding energy between the elongated grains and grain boundary phase became too large, resulting in a decrease in the fracture toughness. The room‐temperature flexural strength was not significantly affected by the Yb2O3 content or the microstructure, other than in the case of 2 wt% addition. The high‐temperature strength in nitrogen, however, increased steadily with Yb2O3 content. The highest strength, 870 MPa at 1400°C, was observed when 16 wt% of Yb2O3 was added. The increase in the high‐temperature strength with Yb2O3 content was attributed to the formation of crystalline Yb4Si2O7N2 phase at the grain boundary.