Papers by Keyword: Spalling

Abstract: Gears in service conditions experience inevitable tooth damage. These damages can cause changes in the time-varying mesh stiffness depending on the mode of damage. The time-varying mesh stiffness of gears is an essential input in calculating gear dynamic responses. Several researchers have evaluated the mesh stiffness of gear teeth with single-mode damage like pitting, spalling, root cracks and wear using either or any combination of analytical, numeric and experimental models. However, limited research has been done on investigating the mesh stiffness of gear teeth undergoing multi-mode damage. In this work, an analytical model is proposed to evaluate the mesh stiffness of a tooth on the pinion with single-mode damage, including pitting, spalling, and surface crack, separately. In addition, a gear tooth with a combination of pits, spalling and surface cracks is also evaluated. The volume of damage on the tooth is kept constant to provide a basis for comparison. The comparison highlights the possible effects of the combined damage modes, which is a more realistic occurrence in gears in service.

Abstract: Electro discharge machining (EDM) as a die sinking process has taken off in 1943. Since then it was known as a non-conventional machining process and its application was limited for processing only electrically conductive materials. Later on, due to the widespread applications, this EDM process is considered conventional as usual. However, in the recent years EDM has gone through considerable changes especially with dielectric fluids, simple to complex geometry, meso to micro sized structures, nanometric surface finish, and so on. In addition, the application of EDM has also been extended for processing electrically semi-conductive and non-conductive materials like ceramics and composites. This paper discussed micro electro discharge machining of non-conductive ceramic materials. It includes detail process development, modelling of material removal rate and surface finish which include the effect of multi spark and random spalling conditions.

Abstract: Kerf-free wafering techniques hold the potential to drastically reduce material losses in semiconductor manufacturing processes. Spalling processes use externally applied stresses to separate crystalline materials along crystal planes with well-defined thickness. Spalled substrates, however, exhibit striations from crack propagation along the crystal, a pattern called Wallner lines. Here, we demonstrate a wafering process that scales favorably for SiC substrates starting from 1 inch in diameter. To eliminate the Wallner line pattern, we use a laser-conditioning process with high numerical aperture at photon energies below the material bandgap energy, using multi-photon effects. The process leads to SiC surfaces with a roughness after spalling of R_a< 4μm.

Abstract: This paper presents the results of an experimental investigation of the impact resistance of UHPFRC slabs. The influence of horizontal and vertical casting of thin slabs against penetration by a projectile is described. The resistance of penetration by a projectile was investigated using projectile with lead core. The results indicate different penetration depths and crater diameters in the target specimens for both kind of casting. Which points on a different arrangement of fibers for horizontal and vertical casting slabs. However, the protective ability is guaranteed in both placement method. Based on the present findings the slabs from ultra-high performance fiber-reinforced concrete casted vertically appear to be most efficient in protection against projectile impact.

Abstract: Fire poses one of the most severe environmental conditions that can act on concrete structures as an external load and can induce severe damages (cracks, spalling) or even lead to collapse. Fire spalling of concrete is a complex phenomenon, which might occur due to pressure build-up in the pores, thermal and load-induced stresses. In this context, ordinary concrete specimens (B40-II and B40-III: fc_28days ≈ 40 MPa) were exposed to standard fire curve (ISO 834-1), while a constant uniaxial or biaxial compressive load was applied. Six different levels of uniaxial compressive stress on cubes and four different levels of biaxial compressive stress on slabs have been investigated. The test results showed that loaded specimens are more susceptible to spalling than unloaded specimens, with increasing amount of spalling for higher values of applied load. It has been found that biaxially loaded specimens are more prone to spalling than uniaxially loaded specimens. B40-II concrete (3% of slag) exhibited higher spalling than the B40-III concrete (43% of slag).

Abstract: Favourable experience with fibre reinforced concrete (FRC) resulted in its increasing use worldwide. The properties of fibre reinforced concrete are mostly influenced by the type and the amount of fibres. Our experimental study was directed to the possible improvements of the residual flexural strength and the properties of concrete exposed to high temperatures with different fibre cocktails including steel, micro polymer or cellulose fibres. The influence of type and amount of fibres on residual flexural strength in cold state were tested after 300, 500 or 800 °C temperature loading.

Abstract: Siliceous concrete (SC) is applied in European Pressurized Water Reactor that is a key component of the third generation nuclear power plant. This paper investigates the mechanical properties and damage evolution of SC (with and without polypropylene fibers) exposed to high temperatures. The mass loss, compressive strength, splitting tensile strength and spalling sensitivity of SC before and after being heated to 200, 400, 600, 800, and 1000 °C are investigated. The ultrasonic testing technique was used to assess the thermal damage, by evaluating the variations of the ultrasonic wave velocity (UWV) for different temperature levels. According to the available literature, a new relationship between damage and UWV was proposed to establish a damage evolution model of SC. The results indicated that: (a) specimens without polypropylene (PP) fibers suffered severe spalling in the range 380-400°C and 470-510°C, while no spalling took place in the specimens with PP fibers in the whole range 25-1000°C; (b) the damage evolution with and without polypropylene fibers was similar, and could adequately be described by means of a Weibull distribution model.

Abstract: More high-rise structures are currently being constructed and correspondingly, the compressive strength of concrete has been increased. However, compared to conventional strength concrete the high strength concrete (HSC) exhibits coarse inner pore structure which blocks escape routes of vapour generated in the event of fire. This results in spalling and subsequently, are responsible for fire vulnerability of the structure. In addition, spalling phenomena is also affected by the section dimensions of HSC which is also another crucial factor from socio-economic considerations. Thus, this study was carried out to evaluate the fire resistance performance of hybrid fiber (i.e. steel-polypropylene-fibre)-reinforced HSC columns with different cross-section dimensions. The result of the fire resistance performance testing using 100MPa concrete showed that delay to failure was observed by approximately 76 per cent.

Abstract: The monitoring and vibratory analysis of gear transmission allow the prediction of a possible malfunction and breakdowns. As the gear transmission product non-stationary signals its treatment is too difficult with the usual tools of signal processing witch can product errors in its interpretation. As the characteristics of gear frequencies are predetermined, it is proposed to monitor (fault identification) using wavelet analysis. To simulate the signal to be analyzed, we intentionally introduced a spalling defect. We chose the Daubechies wavelet type which are the most used in diagnostic. The aim of this work is to try to control the various parameters related to the wavelet analysis for reliable and inexpensive detection, i.e., the order of the wavelet and level decomposition. The approach witch was previously used for bearings, consists on observing the kurtosis for several orders wavelet based on the default severity..

Abstract: As part of an ongoing research project into the numerical prediction of high temperature hygral processes in concrete and fire induced spalling, a fully coupled hygro-thermal model has been formulated for predicting the behaviour of concrete at high temperatures. The hygro-thermal model is a mathematical model for predicting the behaviour of concrete at high temperatures, treating the concrete as a multi-phase semi-saturated porous material. A numerical simulation of a one-dimensional heating experiment performed on an unreinforced concrete slab is presented, demonstrating the effectiveness of the model. A brief discussion of the main hygral processes is presented, in addition to a discussion of numerical challenges arising from the numerical implementation.