Papers by Keyword: Failure Mechanism

Abstract: Shale gas well casing deformation failure is extremely serious in complex fracturing process. Based on the elastic mechanics theory, the distribution law of casing’s maximum equivalent stress field with the non uniform external extrusion is calculated by the complex variable function method. Meanwhile, casing deformation failure mechanism with non uniform external extrusion is revealed. For another, the maximum equivalent stress of the casing is analyzed with the case of a/b=2 and a/b=5. The result shows that the unevenness of the extrusion load has a great influence on the casing maximum equivalent stress distribution. The findings provide technical support for casing design and selection in complex fracturing process of shale gas well. Keywords: shale gas well; complex fracturing; casing formation; failure mechanism

Abstract: According to expansion of electric automobiles, the multi-layer nano thin film glass withheating source is researched to retain safety driving for winter. Generally, the tungsten wire is usedas a heating source of electric automobile glass. Due to its low visibility, silver (Ag) particles areresearched for years. Ag is widely used as a material of heater in the automobile industry since ithas relatively high heat and electrical conductivities. However, the multi-layer nano thin film glassusing Ag particles is under development stage and is not verified in the field, so recall and claimcan be raised. In this study, we will find the potential failure mechanism of the multi-layer nano thinfilm glass based on the properties, and then suggest accelerated life test method to verify 15 years inthe automobile application.

Abstract: In order to improve the mechanical properties of basalt fiber/epoxy composites, carboxylic CNTs were filled into the epoxy matrix of basalt fiber/epoxy composites. Firstly, the carboxylic CNTs filled epoxy composites with different carboxylic CNTs content were studied. Quasi-static and dynamic compression results show that when the content of carboxylic CNTs increased from 0wt% to 1wt%, both ultimate quasi-static and dynamic compressive strength of CNTs filled epoxy composites showed increasing tendencies. However when the content of carboxylic CNTs increased from 1 wt% to 1.5 wt% both ultimate quasi-static and dynamic compressive had decreasing tendencies. Base on above results, carboxylic CNTs (1wt%) filled basalt fiber/epoxy composites were fabricated by mould pressing method. Quasi-static and dynamic compression results showed that both ultimate quasi-static and ultimate dynamic compressive strength of carboxylic CNTs filled basalt fiber/epoxy composite were enhanced compared with those of basalt fiber/epoxy composites without CNTs. However, the critical failure strain were all lower than those of basalt fiber/epoxy composites without CNTs. Failure mechanism analysis showed that the carboxylic CNTs was beneficial for forming good interfacial bonding between epoxy matrix and basalt fibers, and the advantage of high axial tensile strength of basalt fibers could be fully utilized, which is responsible for the enhanced ultimate compressive strength of carboxylic CNTs filled basalt fiber/epoxy composites.

Abstract: The contribution focuses on the description of failure mechanism of atmospheric plasma sprayed multilayer thermal barrier coatings subjected to calcia-magnesia-alumino-silicate (CMAS) environmental attack. To identify exothermic and endothermic reactions which occurred during heating/cooling by means of calorimetry was also utilized initial yttria stabilized zirconia (YSZ) powder subsequently used for thermal spraying of multilayer thermal barrier coating system (TBCs), CMAS powder later on utilized for thin layer deposition and its mixture. Atmospheric plasma spray technique was used to produce the TBCs on a grit blasted nickel-based superalloy substrates, where CoNiCrAlY powder was used for deposition of a bond coat and YSZ powder was sprayed as a top coat. In accordance to the aerospace standard the thin layer of CMAS was deposited on as sprayed TBCs samples surface from its colloidal solution by paint brush method. Burner-rig test, utilizing direct propane-oxygen flame, was used for thermal cyclic exposition of the multilayer coated samples at the temperature of 1150 °C. Samples after thermal cyclic exposure test were investigated by means of materialographic analysis approaches. The significant reduction in life-time of CMAS coated YSZ top coat was observed due to lower melting point phase formation and molten silicate crystallization within the pores providing the spallation identified as a major mechanism of TBCs failure.

Abstract: NiMoB alloy films were deposited on silicon substrate by electroless deposition for diffusion barrier application in copper interconnects technology. NiMoB(40nm)/SiO₂/Si and NiMoB(20nm)/Cu (40nm)/NiMoB(40nm)/SiO₂/Si samples were prepared and annealed at temperatures ranging from 400^◦C to 600^◦C. Samples were characterized by X-ray diffraction (XRD), X-ray photoelectron spectroscopy (XPS), Four Point Probes (FPP) and Atomic Force Microscopy (AFM) to investigate the phases, composition, sheet resistance and surface morphology. The results showed that electroless deposited NiMoB film can be used as an effective Cu diffusion barrier layer until 500^◦C. And the failure mechanism is that NiMoB crystallized and grains grew after annealing at high temperature, a large number of Cu grains passed through NiMoB film via grain boundaries and then reacted with Si substrate and oxygen, causing the generation of highly resistive Cu₄Si and CuO.

Abstract: Rapid freeze–thaw cycle experiments were carried out on concrete specimens with 0.4, 0.5, and 0.6 water–cement (w/c) ratio in 0% (tap water), 1%, and 5% Na₂SO₄ solutions, respectively, to study the performance of ordinary concrete resistance to sulfate freeze–thaw cycle. The specimens underwent visual inspection, and mass losses and relative dynamic elastic modulus (RDEM) were measured regularly. Scanning electron microscope observation and X-ray diffraction analysis were conducted on partial specimens after the freeze–thaw cycle experiment. Research results show that due to the coupling effects of freeze–thaw cycle and sulfate corrosion, freeze–thaw cycles of concrete in Na₂SO₄ solution caused more damages than in tap water. Higher Na₂SO₄ concentration produced severe damages. Concrete with different w/c ratios exhibit different sulfate freeze–thaw cycle resistances, and concrete with lower w/c ratio usually produces stronger resistance. RDEM loss is considered the control index to determine concrete failure. The corrosion products in Na₂SO₄ solution freeze–thaw cycle are mainly ettringite and gypsum. With the increase in Na₂SO₄ concentration, ettringite formation gradually decreases and gypsum formation gradually increases.

Abstract: The cutting performance, failure mechanisms and reliability of Al₂O₃/TiC micro-nanocomposite ceramic tools with different geometry parameters in continuous machining of austenitic stainless steel were studied. The results showed that the largest metal removal amount was got at the cutting speed of 80 m/min, the feed rate of 0.15 mm/r and the cutting depth of 0.1 mm. The failure modes of the tool with small chamfering width and corner radius were mainly cutting edge fracture and tool materials peeling off, which was due to the subcritical crack growth. The life of the tool with small chamfering width and corner radius well followed the Gamma distribution.

Abstract: A Si₃N₄ ceramic tool material with high mechanical properties was fabricated by hot-pressing sintering process. The high speed machining of Inconel 718 tests were carried out with round ceramic inserts. The failure surface and microstructure were analyzed by scanning electron microscopy (SEM) to reveal the ceramic tool failure mechanisms. The results showed that the main failure mechanisms of the Si₃N₄ ceramic tool were flaking, micro-chipping, abrasive wear and adhesive wear in the turning process. On the other hand, chipping, flaking and adhesive wear were the main failure reasons in the milling process. Meanwhile, some small flaking along the cutting edge and step-shaped flaking on the rake face closed to the cutting edge were found on the failure surfaces, which was a typical self-sharpening failure characteristic of the ceramic tool in the high-speed cutting process. This tool failure evolution characteristic of the ceramic tool can be attributed to its higher flexural strength and fracture toughness, which was beneficial to improve the tool life and was constrained by cutting conditions.

Abstract: CoMoB film was prepared on Si substrate via electroless deposition as the diffusion barrier for ULSI-Cu metallization. Annealing experiments of CoMoB(30nm) film and CoMoB(10nm)/Cu (40nm)/CoMoB(30nm)/SiO₂/Si multi-films were carried out in the temperature range from 400^◦C to 700^◦C. Failure temperature and mechanism of Cu diffusion in CoMoB film were discussed. The composition, sheet resistance and morphology of the film were investigated by X-Ray Diffractometer (XRD), Four Point Probe (FPP) and Atomic Force Microscopy (AFM), respectively. It can be concluded that the failure temperature of CoMoB film is 600^◦C. The main reason of failure is that a large number of Cu particles passed through CoMoB grain boundary and reacted with Si substrate to generate Cu₄Si with high resistance.

Abstract: Silver ions migration can cause short circuit between two conductors with different voltage, and it is the main cause of many catastrophic failures in components. Since silver glue is widely used to adhere chips in the components for its low cost, being able to coated automatically and high thermal conductivity. Research on the mechanisms of silver migration is quite important for taking measures to prevent Ag-migration caused failures. In previous studies four factors has been presented which induce a silver ions migration, they are silver material, electric field, humidity, and contamination, but will it be inevitable when the above factors exist In another word, what should we do to prevent the migration In this paper, we confirm that the above four factors are necessary rather than sufficient for silver migration and present a new influence factor on silver migration through a failure analysis case, which gives an important guidance for the reliability design, evaluation and analysis of a component.