Papers by Keyword: Thermal Shock Test

Abstract: The metal would overheat and even burn under the thermal shock arisen as laser drilling, which causes micro-damage inside the metal. Cavitation is the most important origin for crack propagation and failure of metal. To understand the damage mechanism in the heat affected zone of the high temperature nickel based superalloy DD6, an experiment of microvoid nucleation was designed and implemented by laser drilling in DD6 sheet. The complex characteristics of micro-damage including microvoid near the perforation were observed by scanning electron microscopy. An analytic solution of the temperature field in DD6 sheet for thermal shock arisen as laser drilling was obtained on the basis of the non-Fourier heat conduction theory. As a result, the minimum of peak temperature during the thermal shock in the zone of microvoid nucleation was estimated, it can be approximately regarded as critical temperature of nucleation.

Abstract: Reliability failure analysis is extremely important in the manufacturing process of PCB (Printed Circuit Board). In this paper, we use thermal shock test method to analysis the electrical interconnection reliability of PCB in harsh environment. Also taking into account the reliability of PCB is closely related to its design and technology, approaches of technological improvement are proposed. Finally through temperature shock test method, the results show that the reliability of PCB designed with improved technology is enhanced.

Abstract: As a material intended for application in hot-dip galvanization, Ti28.15Al63.4Nb8.25Y (at %) coatings were deposited onto 316L stainless steel substrate using high velocity oxygen fuel (HVOF) and atmospheric plasma spray (APS), respectively. The influence of different thermal spraying techniques on the microstructure, phase transformation, porosity, bond strength and hardness values of Ti28.15Al63.4Nb8.25Y coatings was analyzed by scanning electron microscopy (SEM), X-ray diffraction, tensile test and other analysis methods. In addition, the thermal shock test of Ti28.15Al63.4Nb8.25Y coatings was carried out to evaluate the desquamation resistance and the model of invalidation. The results indicated that HVOF Ti28.15Al63.4Nb8.25Y coatings had more uniform and compact morphology than APS Ti28.15Al63.4Nb8.25Y coating and HVOF Ti28.15Al63.4Nb8.25Y coatings have lower porosity and oxide content. The coatings processed by HVOF had higher bond strength, microhardness and thermal shock resistance and displayed better mechanical properties than that prepared by APS.

Abstract: In this study, the binding performance of a Cercon-based zirconia framework material and special Cercon Ceram S zirconia veneering porcelain is discussed. Rectangular 30 mm × 20 mm × 2 mm porcelain blocks were made from zirconia using the CAD/CAM system. The 2 mm veneering porcelain was then sintered onto blocks at a temperature of 850-800°C with a loading speed of l mm/min. The shear bond strength of the interface was tested. Sintering was studied by visual observation, scanning electron microscopy, energy dispersive spectroscopy (EDS), thermal shock test and other methods. Excellent sintering results of the zirconia framework material and veneering porcelain can be achieved. The cross-sectional morphology of the samples, observed by SEM, shows a uniform, fine, and smooth texture for the veneering porcelain, whereas that of the zirconia framework material shows a rough surface with a uniform and compact texture. EDS results indicate that a small amount of A12O3 and SiO2 is present in the zirconia area, and no ZrO2 or Y2O3 is detected in the veneering porcelain area. No interlayer radial crack or flaw is found throughout the entire thermal shock test of the samples at 60-240°C. Thus, the cracking temperature of the samples is pegged at T>240°C. The shear bond strength of the interface is 32.62±5.77 MPa. Chemical element infiltration exists between zirconia and the veneering porcelain, indicating the chemical bond between the two. An excellent match between the Cercon-based zirconia framework and the special veneering porcelain can be achieved, which can satisfy clinical requirements.

Abstract: Dental ceramic materials do not always show linear expansion behavior. In general, thermal contraction behavior of dental porcelain can be described with the polynomial function: L/L= C+α1 T+α2 T2. In addition, a new method for taking into consideration of nonlinear contraction behavior of dental ceramics is proposed for calculating thermal mismatch value (α) between substrate and veneering materials. Discs of eight substrate/veneer combinations (n=10) were fabricated for thermal shock testing. In this study, a stepwise multiple regression analysis was performed to determine the relationship between thermal shock test results and thermal mismatch value (α) on these combinations. A high degree of correlation was found between αs-b and T. The new method proves to be a reliable one to predict thermal compatibility of multi-layer dental ceramic composites.

Abstract: A unique interferometric system utilizing thermal-conduction loading is developed and implemented to investigate the effect of ramp rates of accelerated test profiles on the thermal deformation of flex package assemblies. The system provides extreme ramp rates to simulate the thermal shock condition with a temperature control much finer than the conventional convection based system can provide. The in-plane and out-of-plane displacements of the flex package are documented through moiré interferometry and Twyman/Green interferometry, respectively. Deformation measured under a thermal shock condition is compared with that under the conventional thermal cycling condition to assess the effect of ramp rates on package deformation. The comparison reveals that a low ramp rate of typical accelerated thermal cycling (ATC) tests causes significant reduction in the maximum level of elastic energy in the package assembly.

Abstract: Thermal shock is a mechanism often leading to failure of ceramic materials that may occur during rapid heating or cooling. These tests were performed in order to compare the thermal shock resistance of ceramic materials by cooling with that of the heating method and hence to evaluate parameters such as thermal shock strength (R1c) and thermal shock fracture toughness (R2c). During the present study, thermal shock resistance of alumina and mullite ceramics was estimated experimentally and theoretically using the thermal shock parameters. The critical thermal stress at the onset of thermal shock fracture was calculated using fracture time, which is measured by an acoustic emission. Results show that thermal shock parameters of alumina specimens decreased with increasing temperature of fracture point. This effect can be attributed to the temperature dependence of the thermal properties. The experimental values of thermal shock parameters evaluated by IRH and WFC techniques were in good agreement at the temperature of fracture point. The thermal shock parameters enabled the definition of a unified thermal shock resistance of ceramics, which is independent of the nature of the testing techniques.

Abstract: Thermal shock test for porous SiC ceramics heated up to testing temperature was performed by a water flow cooling method. In order to find the influence of the penetration for the porous material under the thermal shock, transient temperature distribution was simulated with taking account of the infiltration of the cooling media into the specimen. Thermal stress distributions in the specimens were also calculated from the estimated temperature distributions. In this study, it was evident that the temperature variation of the porous ceramics was more rapid than that of the ceramics without taking account of the penetration.