Papers by Keyword: Thermal Cycling

Abstract: Carbon Fiber Reinforced Composites are presently used in satellites structure for better performance during extreme thermal cycling space environment. These materials display unexpected failure because the satellite periodically goes into and out of the earth shadow region on orbit, leading to a change in its surface temperature. As the coefficient of thermal expansion of carbon fibers is an order of magnitude lower than that of the polymer matrix, repeated thermal stresses are generated in the composites under the alternative temperature field, resulting in damage to the materials and a decrease in mechanical properties. The main objective of this study is to develop an analytical model to predict the damage produce in the composites subjected to extreme thermal loading. These thermal loading also causes the material to release strain energy. The results are presented in terms of strain produced during thermal cycling and also in the process of delamination.

Abstract: The effect of thermal cycling on the martensitic transformation and response characteristics has been studied in bias-SMA spring actuators aged at 350 °C ~ 500 °C. As the number of thermal cycling increases, the Ms temperature of the SMA spring showing only B2→B19' martensitic transformation by aging at 350 or 500 °C goes down. However, SMA spring in which B2→R→B19' martensitic transformation taken place by aging at 400 or 450 °C shows multi-step transformations i.e., M1 and M2 transformations with thermal cycling. The heat flow of M2 transformation increases while the transformation temperature difference between M1 and M2 transformations is enlarged as the number of cycling increases. The recovery displacement and force of bias-SMA spring actuator increase up to the 10th cycle and the extent of increase is the largest at aging temperature of 500 °C. However, both recovery properties decrease after the 10³ or 10⁴ cycles, while the decreasing tendency becomes larger with a rise in aging temperature. Such a change in recovery characteristics of bias-SMA spring actuator with thermal cycling is discussed in connection with training effect or lattice defects introduced during thermal cycling.

Abstract: Effects of thermal cycling on the tensile strength of aluminum alloy welded joints are studied experimentally in this paper. The damage mechanisms are also analyzed based on the microstructure observations. Results reveal that certain thermal cycling can cause strength decrease especially at the heat affected zone of the aluminum alloy welded joint. The cyclic temperature and the external load are the key factors which influence the strength of the welded joint specimens, while the cyclic period has a minor effect in thermal cycling conditions. Microstructure analysis also shows that voids nucleation and evolution governs the damage process under thermal cycling condition.

Abstract: Solder materials are critical packaging compounds and due to usually weakest melting temperature among packaging constitutive materials, thus, they are frequently subjected to a multitude of physical phenomena: creep, fatigue and combined hardening effects. The complexity and interaction of such factors must be considered in suitable way in the mechanical behavior modeling using the appropriate material behavior laws. The choice of the mechanical model depends on several factors such as the complexity of constitutive equations to be integrated, the availability and suitability of implementation in the FE codes, the number of parameters to be identified, the capability of the model to represent the most common physical features of the material… Following these observations and in order to deal with these critical remarks, comparisons between the most common unified viscoplastic models should be done in the local and finite element levels for the decision upon the most efficient model. That is the aim of this paper with application to a tin based solder token as the test material.

Abstract: The thermal cycling (quenching in liquid nitrogen and reverting back to room temperature: austenite martensite reversible transformation) response of Ni-Ti-Fe shape memory alloys has been investigated. It was clearly noted that residual deformation, estimated in terms of noticeable differences in austenite grain size, depend on the relative clustering of fine grains. During repeated thermal cycling, the residual deformation, in-grain misorientation developments and retained martensite content scaled together: bringing out a clear picture of microstructural irreversibility.

Abstract: The solder joints of surface mount components (SMCs) experience thermal degradation culminating in creep and plastic shear strain deformation when subjected to cyclic temperature load over time. Degradation at the joints is due to thermal stress induced by the incompatible, differential and nonlinear expansion mismatch of the different bonded materials in the assembly. The stress magnitude influences the strain behaviour. Plastic strain response of solder joint is critical at the materials interface at the lower part of the joint due to the occurrence of wider variation in the coefficient of thermal expansion of the bonded materials and this may lead to static structural failure. The life expectancy of electronic components reduces exponentially as the operating temperature increases thus making reliability a key concern for electronic systems operating at high temperatures and in harsh environments. This paper reports on the numerical investigation of thermo-mechanical response of a critical BGA joint especially the character of plastic deformation of SnPb solder used in forming the joint as well as the joint’s high temperature reliability. The analysis uses a 3-D models to predict the effect of the transient thermal load on the static structural integrity of a single BGA joint. In this study, the base diameter of solder ball (interface between the PCB, copper pad and the solder) experienced higher damage than the top diameter interconnects. The paper provides a simplified methodology to study the reliability of BGA solder joint at high temperatures excursion.

Abstract: Using elastoplastic finite element method study the interface stress distribution of Sn3.5Ag0.75Cu lead-free solder at different temperatures and different strain rate. Numerical analysis results show that: when strain-rate is identical, as the temperature rises, the interface stress increased rapidly of Sn3.5Ag0.75Cu lead-free solder and the substrate binding sites, from 11 °C when 2.6MPa rose to 90 °C in 49.7MPa, so the temperature is very large have effects of the interface stress of the lead-free solder and the substrate binding sites; when the temperature is constant, as the strain rate increases, Sn3.5Ag0.75Cu lead-free solder and the substrate binding sites of the interface stress showed a slight increase, from 0.005% / S when the 49.47MPa rose to 0.005% / S when the 50.08MPa, so strain rate on lead-free solder and the substrate binding sites of the interface stress effect is very small, indicating Sn3 .5Ag0.75Cu lead-free solder has strong rate-independent nature.

Abstract: Failure of thermal barrier coating (TBC) system is associated with the morphological imperfection of thermally grown oxide (TGO) layer. The objective of this work is to numerically investigate the crack nucleation and propagation in TBC system upon thermal cycling based on a cohesive zone model, in which TGO thickness imperfection effect is incorporated. The results show that TGO/BC (bond coat) interface is subjected to high tensile stress in the vicinity of TGO thickness imperfection during thermal cycling, thereby inducing crack nucleation. Owing to the plastic deformation of BC, fracture behavior of TGO/BC interface is related to BC yield strength for a typical thermal growth rate of TGO. Furthermore, the embedded oxide in BC could be also ruptured as a result of the increasing transverse stress, which will lead to the coalescence of adjacent cracks.

Abstract: The solderability and reliability of SnAgCu and SnAgCuSbBiNi lead-free solders were assessed against SnPbAg solder on a range of PCB finishes. A novel solderability test has been developed to assess the solder system’s ability to realign when a deliberately inaccurate solder stencil printing process was applied. This has shown to be an excellent way to compare PCB finishes and solders, as well as define process parameters. Electroless Nickel Immersion Gold (ENIG) finish proved to give the best solderability and the optimum process parameters were also found. SnPbAg solder has shown superior thermal cycling performance compared to SnAgCu.

Abstract: The effects of thermal cycling and freezing after water absorption on tensile properties of green composites were examined. Jute fiber and matrix were used as the reinforcement and the matrix. The thermal fatigue was conducted as a fatigue test. Heating and freezing process are performed alternately for 0.5h, 1h and 24h during 10 cycles, heating and freezing temperature were 60 and -20 . In a freezing after water absorption, the damage by an expansion of water was examined. The freezing after the water absorption during 1-5 days was performed in a day under the environment of -20 . In thermal cycling, tensile strength and modulus were significantly decreased as the time passes. In 24h-treated test, the decrease rates of tensile strength and modulus were about 50 % compared with that of room temperature. In freezing after water absorption, tensile strength and modulus were decrease compared with that of the room temperature.