Isogeometric analysis of coupled thermo-elastodynamic problems under cyclic thermal shock

To investigate the effect of cyclic thermal shock and mechanical loading on the fracture behavior of magnesia refractories showing different brittleness, the as‐received and cyclic thermally shocked specimens are subjected to monotonic and cyclic wedge splitting test. The whole duration of test is monitored by digital image correlation and acoustic emission. Both thermal and mechanical fatigue resistance increase with the reduction of brittleness. Repetitive thermal shock results in pronounced reduction of strength. However, the specific fracture energy and nonlinearity increase after exposure to thermal shock due to the expanded micro‐crack network inducing the development of a significant fracture process zone. Periodic loading mainly leads to the decrease of strain bearing capacity, as the fatigue loads favor the extension of crack tip instead of fracture process zone expansion. The combined application of periodic thermal shock and mechanical loads gives a new insight into the progressive damage behavior of refractory under critical conditions.

An investigation on the deterioration of physical and mechanical properties of granite after cyclic thermal shock

Study on thermal shock behavior of YSZ abradable sealing coating prepared by mixed solution precursor plasma spraying

Iterative solution of Helmholtz problem with high-order isogeometric analysis and finite element method at mid-range frequencies

Thermal shock behavior of EB-PVD thermal barrier coatings

Marble is a common rock used in many buildings for structural or ornamental purposes and is widely distributed in underground engineering projects. The rocks are exposed to high temperatures when a tunnel fire occurs, and they will be rapidly cooled during the rescue process, which has a great impact on the rock performance and the underground engineering stability. Therefore, the role of cyclic thermal shocks on the physical and mechanical properties of marble specimens was systematically investigated. Different cyclic thermal shock treatments (T = 25, 200, 400, 600, 800 °C; N = 1, 3, 5, 7, 9) were applied to marble specimens and the changes in mass, volume, density and P-wave velocity were recorded in turn. Then, the thermal conductivity, optical microscopy and uniaxial compression tests were carried out. The results showed that both the cyclic thermal shock numbers (N) and the temperature level (T) weaken the rock properties. When the temperature of a thermal shock exceeds 600 °C, the mass loss coefficient and porosity of the marble will increase significantly. The most noticeable change in P-wave velocity occurs between 200 and 400 °C, with a 52.98% attenuation. After three thermal shocks, the cyclic thermal shock numbers have little influence on the uniaxial compressive strength and Young’s modulus of marble specimens. Shear failure is the principal failure mode in marble specimens that have experienced severe thermal damage (high N or T). The optical microscopic pictures are beneficial for illustrating the thermal cracking mechanism of marble specimens after cyclic thermal shocks.

The (TiCr)N hard reactive films with 4 different Ti/Cr atomic ratios are prepared by using multi-arc ion plating. The Ti and Cr targets are used as cathodes in the co-deposition process. The high speed steel (HSS) specimens are adopted as substrate. The thermal shock cycle tests in air cooling (AC) way for the (TiCr)N films are carried out. The test temperatures are chosen as 600 °C and 700 °C, respectively. The changes of the surface compositions and morphology in the thermal shock cycle tests are investigated. The effects of Cr content in the (TiCr)N films, the temperature at which the thermal shock cycle tests are performed and the cycling times on the thermal shock resistance of the (TiCr)N films are discussed and analyzed in detail. The thermal shock behaviors of the (TiCr)N films show that the thermal shock cycling process of the (TiCr)N films consists of two stages, the steady-state oxidation stage with the increase of oxygen content at the early stage of thermal cycles, and, the instable oxidation stage with the oxidation aggravation and the occurrence of the surface cracks. The simple increase of Cr content in the (TiCr)N film does not improve the thermal shock resistance of the (TiCr)N films but easy to aggravate the surface oxidation process during the thermal shock cycles.

This study mainly focuses on site effects of the Ni pad interface on intermetallic compounds (IMCs) characteristic during assembly reflowing, and attempts to provide a reasonable explanation for this particular finding. Besides, the changes of the resulting IMCs characteristic are characterized during thermal shock (TS) cycling, and their potential influences on thermal–mechanical reliability of microjoints are evaluated experimentally and numerically. The results show that the site on the Ni pad interface of silicon chip has great influence on interfacial reaction products, i.e., interfacial IMCs. After bumps soldering, a great amount of larger diamond-shaped (Cu, Ni)6Sn5 compounds were densely packed at the edge region, while some smaller ones were only scattered at the center region. Moreover, substantial particle-shaped (Ni, Cu)3Sn4 compounds as well as some rod-shaped ones emerged at the spaces between the (Cu, Ni)6Sn5 compounds of the center region. More importantly, such site effects were remained in the microjoints during TS cycling, which induced the formation of larger protruding (Cu, Ni)6Sn5 compounds. Finite element (FE) simulation results showed that the stress was mainly concentrated at the top of the protruding (Cu, Ni)6Sn5 compounds, which can be a critical reason to cause the crack occurrence. Furthermore, the underlying mechanism of the interfacial IMCs characteristic induced by the site effects was attempted to propose during bumps soldering.

Cylindrical specimens of Al-20%Si alloys containing primary silicon crystals of different sizes were prepared and their thermal shock behavior was examined. The specimens were quenched into iced water after heated at 550°C for 20 min., and this was repeated. After thermal shock cycles, macroscopic and microscopic examinations were made and the resistance to thermal shock was discussed in relation to the size of primary silicon crystals.1) No crack was observed on the surface of the specimens with refined primary silicon crystals after subjected to the thermal shocks for 400 times. However, some cracks were detected in the central part after about 100 cycles.2) Cracks initiated at the interface between primary silicon and α-aluminum and propagated into the silicon crystal.3) Thermal shock cycles resulted in the deformation of the specimens, but it was confirmed that the resistance to deformation was higher in the specimens with refined primary silicon crystals.4) With an increase in thermal shock cycles, needle-like eutectic silicon changed its shape to spheres, but little change was observed for primary silicon crystals.

The primary objective of the research presented in this paper is to qualify the reliability of mixed assemblies by comparing them to the conventional Sn-Pb assembly and completely Pb-free assembly. The research investigates both forward and backward compatibility in electronic assemblies using a design of experiments (DOE) approach. The investigation utilized a test vehicle containing an area array component (BGA169) and chip components (0603 resistors). Hot air solder leveling (HASL) and organic solderability preservative (OSP) surface finishes were used on the test vehicles to represent Sn-Pb and Pb-free alternatives, respectively. The assembled test vehicles were cut into two panels - one containing a resistor section for isothermal aging and the other containing a BGA and another resistor section for thermal shock. The assemblies were subjected to isothermal aging and thermal shock tests as per Interconnecting and Packaging Electronic Circuits/Joint Electronic Device Engineering Council (IPC/JEDEC) standards. The resistors were sheared in the as-soldered condition, and at various isothermal aging intervals and thermal shock cycles. In order to simulate an intermetallic failure in isothermal aging, a reduced shear height (20 mum) was used for the shear test. The performance of the resistor solder joints were quantified in terms of the shear force. The performance of the ball grid array (BGA) solder joint during thermal shock testing was quantified in terms of the number of cycles to failure. Experimental results from shear analysis of resistor solder joints show that Pb-free alloy assemblies' performance is superior to those assembled using Sn-Pb alloy. Also, the ductile nature of the Sn-Ag-Cu (SAC) alloy provides the joints a better fatigue life. With the area array components, Pb-free assembly joints outlived the traditional Sn-Pb joints when subjected to thermal shock loading. Among the mixed assemblies, backward-compatible assemblies (Pb-free bumps and Sn-Pb solder alloy) showed superior performance. The microstructural analysis of the solder joints indicate a uniform distribution of lead in the solder joint matrix.

Dynamic splitting tensile behaviors of red-sandstone subjected to repeated thermal shocks: Deterioration and micro-mechanism

Dynamic analysis of two-dimensional elasticity problems using the Isogeometric analysis method and its comparison with the finite element method is the subject of this research. For this purpose, formulation of the governing differential equation is obtained by using the B-spline basis functions. Some numerical examples employing consistent and lumped mass matrices are presented in order to compare the results of Isogeometric analysis and finite elements. The effect of increasing the number of control points and the degree of B-spline basis functions on the accuracy of the solution are also investigated. Furthermore, since the Newmark method is employed for transient dynamic analysis, the effects of parameters α and β on the solution accuracy are investigated. The obtained results demonstrate higher accuracy of the isogeometric analysis method in comparison with the FEM, despite employing fewer numbers of degrees of freedom and consequently reduction in the dimensions of system of equations and computational effort.

NiCoCrAlY coatings strengthened by different content of nano-Al2O3p, using crosscurrent CO2 laser, were prepared on Ni-based superalloy substrates, and thermal shock behaviors of these coatings were investigated by cycling between 1050°C and room temperature (forced water quenching).The results show that the thermal shock resistances of nano-Al2O3p-added coatings are definitely better than that without adding nano-Al2O3p. Among the nano-Al2O3p-added coatings, the coating added with 0.5wt% nano-Al2O3p performs best. After 10 thermal shock cycles, the spalled and spalling area in the oxide scale of the no-nano-Al2O3p coating reaches up to 27.7%, and the main failure form of the oxide scale is an expanding unit-spalling type in thermal shock cycles. While the area in the oxide scale of nano-Al2O3p-added coatings is only 10%~60% to the no-nano-Al2O3p one, and the failure of these oxide scales is mainly in the form of unit-spalling type. After 100 thermal shock cycles, many cracks turn up in the cross-section of the no-nano-Al2O3p coating, including propagating crack and internal crack. While no internal crack appeared in nano-Al2O3p-added coatings, and the propagating cracks are smaller than no-nano-Al2O3p one.

Sealants that can guarantee long-term wellbore sealing integrity are of great significance to the safe and sustainable storage of CO2 in carbon capture and storage (CCS). In this study, we investigate how abrupt cyclic thermal shocks affect the integrity of four sealants of different compositions. These sealants include two reference OPC-based blends (S1 and S2), one newly-designed OPC-based blend that contains CO2-sequestering additives (S3), and one calcium aluminate cement (CAC)-based blend designed for CCS applications (S4). We have measured the thermal properties of these samples, followed by quenching and flow-through experiments to apply strong cyclic thermal shocks on samples of the four sealants, where we heated the samples to 120 °C, and quenched them in, or flowed through water of 20 °C. Using X-ray tomography (32 µm/voxel) before and after the experiment showed that both S1, S2 (reference OPC-based) and S4 (CAC-based) broke after thermal-shocking experiments. Cracks and new voids developed in the samples. Post-treatment strength testing shows that thermal shocks reduce the unconfined compressive strength of these three sealants. This implies that these compositions may not be optimal materials for long-term wellbore sealing during CO2 injection and storage afterward. For all these three sealant compositions, quenching resulted in a greater reduction in strength (by 53 % on average) than flow-through experiments (by 29 % on average). On the contrary, we have not observed any cracks after either quenching or flow-through experiments in S3 sealant (OPC with CO2-sequestering additives). We attribute the intactness of this sealant after thermal shocks to its higher thermal diffusivity than the other three sealants. Heat transfers more rapidly in this sealant and the associated thermal stresses are mild and insufficient to cause any damage to its integrity, which makes this sealant a good candidate for wellbore sealing material that can effectively withstand strong thermal shocks encountered during CCS, though further studies are required.

Influence of high flux hydrogen-plasma exposure on the thermal shock induced crack formation in tungsten