Indentation mechanics and fracture behavior of metal/ceramic nanolaminate composites

Composite laminates on the nanoscale have unique properties, such as high strength, high wear resistance, and biocompatibility. In this paper we report on the nanoindentation behavior of a model metal–ceramic nanolaminate consisting of alternating layers of aluminum and silicon carbide (Al/SiC) processed by PVD on a Si substrate. Composites with different layer thicknesses were fabricated and the effect of layer thickness on Young’s modulus and hardness was quantified. The effect of indentation depth on modulus and hardness was studied. The damage that took place during nanoindentation was examined by cross-sectioning the samples by focused ion beam (FIB) technique and imaging the surface using scanning electron microscopy (SEM). Finite element modeling (FEM) of nanoindentation of nanolaminates was conducted. The damage patterns observed in experiments were qualitatively supported by the numerical simulations.     

Microstructures and mechanical properties of Ti3Al/Ni-based superalloy joints brazed with AuNi filler metal

For the purpose of high-temperature service and the weight reduction in aviation engineering applications, the dissimilar joining of Ti₃Al-based alloy to Ni-based superalloy (GH536) was conducted using Au-17.5Ni (wt%) brazing filler metal. The microstructure and chemical composition at the interfaces were investigated by scanning electron microscope, X-ray diffraction and transmission electron microscope. The diffusion behaviors of elements were analyzed as well. The results indicated that the Ti₃Al/GH536 joint microstructure was characterized by multiple layer structures. Element Ni from Au-Ni filler metal reacted with Ti₃Al base metal, leading to the formation of AlNi₂Ti and NiTi compounds. Element Ni from Ti₃Al base metal reacted with Ni and thus Ni₃Nb phase was detected in the joint central area. Due to the dissolution of Ni-based superalloy, (Ni,Au) solid solution ((Ni,Au)ss) and Ni-rich phase were visible adjacent to the superalloy side. The average tensile strength of all the joints brazed at 1253 K for 5–20 min was above 356 MPa at room-temperature. In particular, the joints brazed at 1253 K/15 min presented the maximum tensile strength of 434 MPa at room-temperature, and the strength of 314 MPa was maintained at 923 K. AlNi₂Ti compound resulted in the highest hardness area and the fracture of the samples subjected to the tensile test mainly occurred in this zone.     

Three-dimensional elastic stress analysis of a fracture specimen with an edge crack

A numerical stress analysis of an elastic three-dimensional specimen similar to the compact tension specimen used in fracture investigations is presented. The numerical results are achieved using singular integral equations which are analogous to Green's boundary formula in potential theory. The analysis yields details of the stresses near the crack tip and clearly shows their three-dimensional character. Some results are also given to indicate the influence of thickness and Poisson's ratio on the stresses.

---

Zusammenfassung Es wird für eine dreidimensionale elastische Probe, ähnlich der kompakten Zugprobe für Bruchuntersuchungen, eine zahlenmässige Analyse der Spannungen dargelegt. Die numerischen Ergebnisse wurden über singulare Integralgleichungen analog den Greenschen Formeln in der Potentialtheorie ermittelt. Die Untersuchung ergibt Einzelheiten über die Spannungen in der Umgebung der Rißspitze und zeigt klar deren dreidimensionalen Charakter. Es werden auch einige Resultate mitgeteilt die den Einfluß der Dicke und des Poissonschen Moduls auf die Spannungen herausstellen.

---

Résumé On présente une analyse numérique des contraintes dans une éprouvette à trois dimensions en sollicitation dans le domaine élastique, éprouvette similaire à l'éprouvette de traction utilisée dans les études de mécanique de rupture.Les résultats numériques sont obtenus en recourant à des équations à intégrales singulières, qui sont analogues à l'équation aux limites de Green dans la théorie du potentiel.L'analyse conduit à fournir la distribution complète des contraintes au voisinage de l'éxtremité de la fissure et démontre clairement le caractère tridimensionnel de celle-ci.L'influence de l'épaisseur et du module de Poisson sur les contraintes est également dégagée de certains résultats qui ont été obtenus.

     

Electrical characterization of CMOS transistors subject to externally applied mechanical stress

Hole and electron mobilities in CMOS structures are significantly influenced by a mechanical strain state. In the present work a new experimental device has been designed, able to apply a uniaxial in-plane strain along different crystallographic orientations. A hole mobility enhancement of +10% and an electron mobility decrease of −5% have been demonstrated with the application of a 0.05% compressive 1 1 0 strain; a hole mobility enhancement of +2% and an electron mobility decrease of −3% have been induced into the material with the application of a 0.05% compressive 1 0 0 strain.     

Influence of shape and size on residual stress in ceramic/metal joining

The effects of shape and size on the residual stress on the surfaces of silicon nitride/Invar alloy joints have been examined by means of the strain gauge method. The highest residual stress perpendicular to the interface appeared near the corners in the rectangular bond face joint. It was tensile in the silicon nitride and compressive in the Invar alloy. The highest tensile stress in the rectangular bond face joint was larger than that in the circle bond face joint. The larger the diameter of the cylindrical joint used, the larger was the tensile stress induced. The residual stress parallel to the interface was compressive in silicon nitride while that in the Invar alloy was tensile.     

Influence of shape and size on residual stress in ceramic/metal joining

Effects of shape and size on the residual stress on the surfaces of silicon nitride/Invar alloy joints have been examined by means of the strain-gauge method. The highest residual stress perpendicular to the interface appeared near the corners in the rectangular bond face joint. It was tensile in the silicon nitride and compressive in the Invar alloy. The highest tensile stress in the rectangular bond face joint was larger than that in the circle bond face joint. The larger the diameter of the cylindrical joint the larger was the tensile stress induced. The residual stress parallel to the interface was compressive in silicon nitride while that in the Invar alloy was tensile.     

Effect of annealing treatment on mechanical properties of a ZrB2-SiC-graphite ceramic

The ZrB₂-SiC-graphite (ZSG) ceramic was annealed at 1600, 1700 and 1800 °C for different times, respectively. It was revealed that the annealing treatment is favorable to increase the interface bonding and relative density, and to decrease the thermal residual stress, to result in the crimp of the graphite flake. It was the optimal annealing treatment process conditions of 1700 °C and 90 min according to the best combination of the mechanical properties. To compare the mechanical properties of the specimen before the annealing treatment, the hardness, strength and toughness of the specimen annealed at 1700 °C for 90 min were enhanced by 20.6% and 20.2%, decreased by 8.2%, respectively.     

A thermodynamic analysis of ceramic oxide/liquid metal interfaces

Abstracts are not published in this journal This revised version was published online in November 2006 with corrections to the Cover Date.     

On the stress singularities at the intersection of a cylindrical inclusion with the free surface of a plate

Utilizing the form of a general 3D solution, the author investigates analytically the stress field in the neighborhood of the intersection of a cylindrical inclusion and a free surface. The inclusion is assumed to be of a homogeneous and isotropic material and is to be embedded in an isotropic plate of an arbitrary thickness. The stress field is induced by a uniform tension applied on the plate at points far remote from the inclusion (see Fig. 1).The displacement and stress fields are derived explicitly and a stress singularity is shown to exist for the case when the inclusion is stiffer than the plate material. Moreover, the stress singularity is shown to be a function of the respective ratios of the shear moduli and Poisson's.The special case of G ₂0, G ₂=G ₁ and G ₂ are also investigated.

---

Résumé En utilisant la forme d'une solution générale à trois dimensions, l'auteur analyse le champ de contraintes au voisinage de l'intersection d'une inclusion cylindrique et d'une surface libre. On suppose que l'inclusion est constituée d'une matériau homogène et isotrope, et qu'elle est insérée dans une plaque isotrope d'épaisseur arbitraire. Le champ de contraintes et dû à une tension uniforme appliquée en des points suffisamment éloignés de l'inclusion.On exprime de manière explicite les champs de déplacements et de contraintes, et on montre qu'il existe une singularité de la contrainte dans le cas où l'inclusion est dans un matériau plus rigide que celui de la plaque. En outre, on montre que la singularité de la contrainte est fonction des rapport respectifs des modules de cisaillement et de Poisson.On étudie également les cas spéciaux G ₂0, G ₂=G ₁ et G ₁.

     

Review: mechanical behavior of metal/ceramic interfaces in nanolayered composites—experiments and modeling

Recent experimental and modeling studies in nanolayered metal/ceramic composites are reviewed, with focus on the mechanical behaviors of metal/nitrides interfaces. The experimental and modeling studies of the slip systems in bulk TiN are reviewed first. Then, the experimental studies of interfaces, including co-deformation mechanism by micropillar compression tests, in situ TEM straining tests for the dynamic process of the co-deformation, thickness-dependent fracture behavior, and interrelationship among the interfacial bonding, microstructure, and mechanical response, are reviewed for the specific material systems of Al/TiN and Cu/TiN multilayers at nanoscale. The modeling studies reviewed cover first-principles density functional theory-based modeling, atomistic molecular dynamics simulations, and mesoscale modeling of nanolayered composites using discrete dislocation dynamics. The phase transformation between zinc-blende and wurtzite AlN phases in Al/AlN multilayers at nanoscale is also reviewed. Finally, a summary and perspective of possible research directions and challenges are given.     

A stress concentration due to edge damage in a rectangular boron-epoxy sheet

The stress field in a square sheet of epoxy-boron composite with damaged fibers is determined for the case of applied uniform normal stress longitudinal to the fibers. The damage model assumes that damaged fibers are exactly as effective as the matrix and that the distribution of undamaged fibers can be given by polynomial. A Ritz solution for the displacements is obtained and used to investigate the stresses. A stress concentration is found and described. The energy release rate curve for a family of progressive damage configurations is exhibited.     

受机械力作用金属／陶瓷功能梯度板主共振奇异性

研究机械力作用下金属，陶瓷功能梯度薄板主共振奇异性问题。按照功能梯度薄板的非线性动力学方程，得到金属，陶瓷功能梯度薄板受横向机械力作用的非线性振动方程。应用非线性振动的多尺度法得到系统主共振幅频响应分岔方程并进行奇异性分析，求得幅频响应分岔方程在开折参数平面的转迁集和分岔图。     

A TEM analysis of the Si3N4/Si3N4 joint brazed with a Cu-Zn-Ti filler metal

Si₃N₄ ceramic was joined to itself using a filler alloy of (CuZn)85Ti15 at 1123–1323 K for 15 min. TEM observation showed that a reaction zone of TiN and/or Ti₂N exists at the interface between the ceramic and filler alloy, and the center of the joint is composed of Cu-Zn solid solution in which there are Cu₂TiZn and Ti₅Si₃ reaction phases. With increasing brazing temperature, both the thickness of the reaction zone and the amount and size of the Ti₅Si₃ phase increase, while the amount and size of the Cu₂TiZn phase decrease. When the brazing temperature reached 1323 K, the Cu₂TiZn phase disappeared. When the brazing temperature is lower than 1223 K, the interfacial reaction zone is mainly composed of Ti₂N, which has a cylindrical shape and orientates randomly in the zone. There is a crystal orientation relationship between the Ti₂N in the reaction zone and the Cu in the Cu-Zn solid solution, which is: {110}_Ti2N//{420}_Cu, 001_Ti2N//001_Cu. When the brazing temperature is higher than 1223 K, the interfacial zone is composed of TiN, which has a plate shape crossing each other.     

A crack growth resistance curve approach to fiber/metal laminate fracture toughness evaluation

Fiber/metal laminates consist of thin, high strength aluminum alloy sheets alternately bonded to plies of fiber-reinforced epoxy adhesive. This new class of material combines the best features of organic matrix composites and metals. Tests conducted on wide centrally slotted panels show that fiber/metal laminates, like metals, exhibit capacity for slow stable tearing prior to rapid fracture. It is also shown that a fracture mechanics based R-curve approach, similar to that used for metals, can be applied to predict effects of size and geometry on slotted laminate panel residual strength. These results represent an important step in the development of analytical practices for fiber/metal laminate damage tolerance and airworthiness assessments.     

受机械力作用金属／陶瓷功能梯度板的亚谐共振研究

研究机械力作用下金属，陶瓷功能梯度薄板1／3次亚谐共振问题。按照功能梯度薄板的非线性动力学方程，得到金属，陶瓷功能梯度薄板受横向机械力作用的非线性振动方程。应用非线性振动的多尺度法得到系统1／3次亚谐共振近似解并进行数值计算。分析阻尼、激励、几何尺寸等参数对系统1／3次亚谐共振幅频响应曲线的影响。     

受机械力作用金属／陶瓷功能梯度板的超谐共振研究

研究机械力作用下金属／陶瓷功能梯度薄板3次超谐共振问题．按照功能梯度薄板的非线性动力学方程，得到金属／陶瓷功能梯度薄板受横向机械力作用的非线性振动方程。应用非线性振动的多尺度法得到系统3次超谐共振近似解并进行数值计算。分析阻尼、激励、几何尺寸等参数对系统3次超谐共振幅频响应曲线的影响．     

受机械力作用金属／陶瓷功能梯度板的非线性振动模型

研究机械力作用下金属，陶瓷功能梯度薄板的建模问题。应用弹性理论和Galerkin方法建立小挠度金属，陶瓷功能梯度薄板受横向机械力作用的非线性振动方程。     

A simple model of work hardening applied to post-yield fracture mechanics

International Journal of Fracture -