Path-Independent integral for fracture of solids under combined electrochemical and mechanical loadings

It is well known that invariant or path-independent integrals provide a powerful tool in the study of crack initiation and growth in functional materials. It is shown in this article that the classical J-integral is no longer path-independent when the solid is under combined electrochemical and mechanical loading. A modified J-integral is derived that is path-independent under electro-chemo-mechanical equilibrium. To illustrate the utilization of this modified J-integral, the delamination of a thin elastic film from an infinitely thick elastic substrate is considered under chemo-mechanical equilibrium. Within the membrane approximation, the problem reduces to finding stress and solute concentration in a thin membrane adhered to the substrate. By adopting a linearized chemo-mechanical model, this problem is solved semi-analytically. The solution is then used to demonstrate that the classical J-integral is path-dependent, whereas the modified J-integral derived in this article is path-independent

A Non-Collinear Mixing Technique to Measure the Acoustic Nonlinearity Parameter of Adhesive Bond from Only One Side of the Sample

The acoustic nonlinearity parameter (ANLP) of a material is often positively correlated with the damage in the material. Therefore, the ability to nondestructively measure the ANLP may enable the nondestructive characterization of the material’s remaining strength. In this work, we developed a non-collinear mixing technique to measure the ANLP of adhesive bonds. One of the most significant features of the new method is that it requires only one-side access to the adhesive bond being measured, which significantly increases it utility in field measurements. Specifically, the test sample considered in this study consists of two aluminum plates adhesively joined together through a commercial adhesive tape. The non-collinear wave mixing technique consists of generating a longitudinal wave and a shear wave by piezoelectric transmitters attached to the same surface of the sample under test. These waves are introduced into the sample in such an angle that they will mix at the adhesive bond region. Mixing of these two waves generates a shear wave that propagates back towards the surface where the two waves were generated. This mixing wave is then recorded by a shear wave receiver placed on the same surface where the longitudinal and shear wave transmitters are located. It was shown that amplitude of this mixing wave is proportional to the ANLP of the adhesive bond. To demonstrate the effectiveness of the newly developed technique, a freshly made adhesive sample was first measured using the non-collinear mixing technique to obtain the ANLP of the adhesive bond. This sample is then placed inside a thermal chamber for aging to change its ANLP. The sample was taken out the thermal chamber periodically to measure its ANLP. The measured results clearly show that the ANLP varies with aging time. Initially, the ANLP decreases with aging time, possibly due to further curing. Afterward, the ANLP begins to increase with aging time, likely due to aging induced damage in the polymer adhesive. To verify that the signals received from the shear wave receiver are indeed the mixing wave, the finite element method was used to simulate the wave motion in the test sample. The simulation results clearly show that the signals recorded by the shear wave receiver are indeed the desired mixing wave, whose amplitude is proportional to the ANLP of the adhesive bond

EFFECT OF MOISTURE ON THE ELASTIC MODULUS AND INTERFACIAL ADHESION OF POLYMER-METAL COMPONENTS IN MICROELECTRONIC ASSEMBLIES

ABSTRACT Moisture poses a significant threat to the reliability of microelectronic assemblies and can be attributed as being one of the principal causes of many premature package failures. It is a multi-dimensional concern in electronic packaging, having an adverse effect on package reliability by changing both the mechanical properties and interfacial adhesion of the microelectronic assembly. In this paper, a study has been conducted to evaluate the moisture-induced degradation of both the elastic modulus of a commercially available no-flow underfill and the interfacial adhesion of the underfill to a copper alloy substrate. Three different levels of moisture preconditioning, 85C/50%RH, 85C/65%RH, and 85C/85RH%, were implemented in this study. Diffusion coefficient test specimens were constructed to experimentally measure the moisture diffusivity into the underfill resin and obtain the moisture saturation concentration for each level of moisture preconditioning. Flexural bend test specimens were made to characterize the effect of moisture on the elastic modulus of the underfill adhesive. Last, interfacial fracture toughness specimens with prefabricated interface cracks were used in a four point bending test to quantify the effect of moisture on interfacial fracture toughness. The results of this study will aid in the development of more robust microelectronic assemblies, demonstrating how both the elastic modulus and interfacial toughness change as a function of moisture concentration. INTRODUCTION Microelectronic packaging is a very transient, rapidly progressing technology. With interconnect density increasing and package size decreasing, several adaptations to microelectronic assemblies have been developed t

Determination of Absolute Material Nonlinearity in Aluminum and Fused Silica with Air-Coupled Ultrasonic Receivers

Knowledge of the absolute material nonlinearity parameter, β, of a specimen allows for quantitative evaluation of its current microstructural state, making it a powerful tool in the NDE toolbox. However, the various methods used in the past to measure β each suffer from significant limitations. Piezoelectric contact transducers, while easy to use in many ways, are hindered by the unreliability of the interfacial contact between transducer and specimen surface, which offsets their high sensitivity to nonlinear signals. Laser interferometry provides non-contact detection, but requires carefully prepared specimens or expensive and complicated optics to maximize sensitivity to the nonlinear components of a received waveform, and additionally is expensive and relatively difficult to use in the field. Air-coupled piezoelectric transducers offer the strengths of both of these technologies and the weaknesses of neither, but are notoriously difficult to calibrate for use in nonlinear measurements. This work proposes a hybrid modeling and experimental approach to air-coupled transducer calibration and the use of this calibration in a model-based optimization to determine the β parameter of the material under investigation. This approach is applied to aluminum and fused silica, which are both well-documented materials and provide a strong reference for comparison of experimental and modeling results

Longitudinal Changes In Chinese Minority College Students\u27 Health-Related Fitness: A Multilevel Latent Growth Curve Modeling Approach

Purpose: The study aimed to test the overall changes of health-related fitness (HRF) in minority Chinese college students and to examine HRF differences in gender, race, and year in college. Method: Participants (n = 1320) were minority college students with more than two-thirds females (ie 76.1%), and Hui, Tibetan, and Mongolia consisted of 13.8%, 13.8%, and 11.2%, respectively. Student HRF was tracked for four years. Data were analyzed using multilevel latent growth curve modeling. Results: Muscular strength and endurance were the weakest component in minority college students’ HRF, while body mass index was within the category of “excellent”. Males outperformed female on all components of HRF. Conclusions: It is suggested that interventions concerning minority females’ HRF and muscular strength and endurance for both genders be constructed and tested

The impact of ocean acidification and cadmium on the immune responses of Pacific oyster, Crassostrea gigas

Seawater acidification (OA) and cadmium (Cd) has the potential to lead to immunosuppression effect on marine bivalves. However, the interaction between these two environmental stressors on immune system of marine bivalves has received limited attention. In order to evaluate the defense responses of oysters under the combined exposure to OA and cadmium, the oysters Crassostrea gigas were exposed to 10 mu g/L Cd at three pH levels (8.1, 7.8 and 7.6) for 31 days. Results showed that OA exposure alone led to increased DNA damage, apoptosis rate and ROS production of hemocytes. However, inhibited phagocytosis rate, combined with increased DNA damage, apoptosis rate and ROS production of hemocytes were observed in oysters under exposure to Cd exposure alone or combined with OA. Significant interactive effects between OA and Cd were observed on ROS production and DNA damage of hemocytes. In addition, there is generally significant increase in the mRNA expression of genes related to immune-related TLR pathway and two immune factors (TNF and integrin beta-1B) in Cd-exposed oysters at pH 7.6. The results revealed that even though the mRNA expression of genes related to immune responses (TLR pathway and immune factors) was stimulated to counteract the immunosuppression caused by acidified seawater and Cd, depressed hemocyte function perhaps sensitized oysters to potential pathogen infection

Characteristics of second harmonic generation of Lamb waves in nonlinear elastic plates

© 2010 Acoustical Society of America. The following article appeared in Journal of the Acoustical Society of America, Vol. 127, No. 4 (April 2010) and may be found at http://dx.doi.org/10.1121/1.3294714DOI: 10.1121/1.3294714This paper investigates the characteristics of the second harmonic generation of Lamb waves in a plate with quadratic nonlinearity. Analytical asymptotic solutions to Lamb waves are first obtained through the use of a perturbation method. Then, based on a careful analysis of these asymptotic solutions, it is shown that the cross-modal generation of a symmetric second harmonic mode by an antisymmetric primary mode is possible. These solutions also demonstrate that modes showing internal resonance-nonzero power flux to the second harmonic mode, plus phase velocity matching-are most useful for measurements. In addition, when using finite wave packets, which is the case in most experimental measurements, group velocity matching is required for a cumulative increase in the second harmonic amplitude with propagation distance. Finally, five mode types (which are independent of material properties) that satisfy all three requirements for this cumulative increase in second harmonic amplitude-nonzero power flux, plus phase and group velocity matching-are identified. These results are important for the development of an experimental procedure to measure material nonlinearity with Lamb waves