Fatigue performances of critical structures are strongly affected by the microstructural (e.g. grain, defect, inclusion, etc.) size effect, and it is thus important to quantify their detrimental effect. In this work, a numerical procedure is constructed to quantify the influence of microstructure on the mechanical and fatigue behaviors of Ni-based superalloy GH4169. Specifically, by combining sub-modelling approach with crystal plasticity constitutive model, a dual-scale modelling approach is developed for studying grain-level mechanical behavior of Ni-based superalloy GH4169 notched components. In addition, the dislocation-based Tanaka-Mura-Wu model is applied for fatigue crack initiation life prediction. The Paris law is then utilized for fatigue crack propagation analysis based on the simulated short crack. To study the microstructural size effect on fatigue crack initiation and propagation behaviors, sub-models containing various grain orientation, grain size, defect size/shape are built and analysed. Finally, a series of fatigue tests on notched specimens of Ni-based superalloy GH4169 were carried out for method validation. Results indicate that the established dual-scale modelling approach and fatigue life prediction framework yields good agreement with experimental results. 

Microstructural size effect on the notch fatigue behavior of a Ni-based superalloy using crystal plasticity modelling approach

Nanoindentation has been widely utilized for measuring mechanical properties at small scales over the past three decades. Indentation size effect (ISE) is a crucial phenomenon in nanoindentation testing of crystalline materials, which is usually manifested as an increase of hardness with a decrease of indent size. Tremendous efforts have been made to understand ISE with the aim of eliminating its influence on determining the intrinsic mechanical properties. More importantly, ISE is a key phenomenon for exploring the unique deformation mechanisms of crystalline materials at the nanoscale. We critically review the experimental observations of ISE in crystalline materials, focusing on the influences of the indenter geometry and crystal structure. In addition, the mechanistic models proposed for ISE as well as recent findings by numerical simulations are also examined in detail to explore the origins of ISE and identify the unsolved challenges. 

Review of indentation size effect in crystalline materials: Progress, challenges and opportunities

In order to create alloys with exceptional properties for orthopedic uses, this study focuses on the impact of zirconium (Zr) content on the structural, electrochemical, and tribological qualities of nanostructured Ti–25Nb-xZr [x = 5, 10, 15, 20, 25, and 30 atomic (at.) %] alloys. The structural evolution was investigated using XRD and SEM techniques. The mechanical characteristics of the produced alloys, including Vickers hardness and Young's modulus, were measured. In addition, the corrosion tests were performed using the OCP, EIS, and PD methods in Ringer's solution within the independent pH range at 37 °C. A ball-on-disc tribometer was used to investigate the tribological behavior of the alloys under various loads and wet conditions using the Ringer solution. It has been verified that Zr content (at. %) in the alloys had an impact on their morphologies, structural evolution, and mechanical characteristics. According to the morphological analysis, the particle and crystallite size decreases with increasing Zr content. Young's modulus and Vickers hardness show the same tendency. The EIS data demonstrated that a single passive film formed on the alloy surfaces, and the addition of Zr enhanced the corrosion resistance of the passive films. The polarization curves demonstrate that the alloys had low corrosion current densities and large passive areas without the passive films disintegrating. Likewise, the inclusion of Zr resulted in a reduction in the corrosion and passive current densities values. All of these results suggested that the titanium alloys exhibit a more noble electrochemical activity caused by Zr. From the tribological perspective, it was found that the friction coefficient of the alloys reduced with increasing Zr content. 

Investigating the effect of Zr content on electrochemical and tribological properties of newly developed near β-type Ti-alloys (Ti–25Nb-xZr) for biomedical applications

In this study, the surface of new lapping films was analyzed, and the lapping finishing process was applied to RG7 tin bronze alloy. The research focused on examining lapping films with electrocorundum grains of nominal sizes 30, 12, and 9 μm, commonly used for achieving smooth surfaces. The manufacturing process involves placing abrasive grains and binder onto a polyester tape, resulting in a heterogeneous distribution of abrasive grains. The study investigates the impact of this random distribution on the performance of lapping films during material removal. Scanning electron microscopy was used to analyze the surface structure of abrasive films, revealing distinctive structures formed by the specific aggregation of abrasive grains. This study explores the influence of different nominal grain sizes on surface finish and aims to optimize lapping processes for diverse applications. The research also delves into microchip analysis, examining the products of the lapping film finishing process. Microchips were observed directly on the abrasive tool surface, revealing insights into their morphology and distribution. The chip segmentation frequency was determined, and they amounted to approximately 0.8 to 3 MHz; these are very high frequencies, which are unique for known chip-forming processes.

Morphology of Microchips in the Surface Finishing Process Utilizing Abrasive Films

Understanding how different hybrid composite designs under flexural, interlaminar shear and fracture is the objective of this study. The hybrid composite was manufactured utilizing the hand-layup process to produce three different laminate arrangements beside the neat composite. The effects of PC integration and position through the hybrid composites were evaluated, and an analysis of the damage mechanisms was performed. The results demonstrated that incorporating the PC sheet resulted in an improvement in overall performance. Additionally, delamination was determined to be the most prevalent type of failure, followed by fiber and matrix breakage and plastic deformation of PC sheet. 

Hybridization of thermoplastic/glass fiber reinforced epoxy composites for lightweight structures

Meso-scale low-cycle fatigue damage of polycrystalline nickel-based alloy by crystal plasticity finite element method

As a widely used die-attach material for interconnected structures, sintered silver nanoparticles (AgNPs) exhibit high electrical conductivity and excellent thermal conductivity properties. This paper develops a framework of crystal plasticity (CP) finite element method from the dislocation slip mechanism and applies it to interconnected structure of sintered AgNP materials, based on which the thermal stress simulation under temperature cycling is completed. Firstly, a polycrystalline model for sintered AgNP with the required meso-scale structure is established using Abaqus software. Further, the macroscopic stress-strain behavior for sintered AgNP is accurately described by defining the CP constitutive parameters, which are directly influenced by the crystal orientations and slip systems. By the comparison of the simulation results and the experimental data, the validity and reasonableness of the proposed model are verified. Finally, a typical interconnect structure in power modules with the sintered AgNP material between the SiC chip and the metallization layer is established. By applying the temperature cycling to the entire interconnected structure, the temperature and stress distribution characteristics of the sintered AgNP layer are analyzed. The results show that the distributions of temperature and stress differ between the different grains due to differences in grain orientation and slip system orientation. Notably, significant stress concentrations are found in the area around the pores, indicating that cracks are likely to develop along the pores and expand further, leading to fracture of the material.

Meso-scale crystal plasticity modeling of sintered silver nanoparticles in typical interconnected structures

Nanoindentation experiments have been attracting more attentions to in situ test the mechanical properties of die-attach materials due to the localized loading features. Load controlled manner is usually performed to maintain the indentation strain rate, which results in great challenges for finite element (FE) simulations with the indenter controlled in a displacement manner. In this paper, a validated dimensionless method is adopted to describe the applied load–penetration depth (P–h) curve, where the loading curvature represents the mechanical properties of the materials of interest. Based on a typical FE simulation by using the Berkovich indenter, the relationship between load and displacement controlled methods is investigated. The reaction force on the indenter can be measured from the FE simulations controlled by the applied displacement of the indenter. Meanwhile, the P–h curve of indentations controlled by load can be predicted by the proposed method with the provided loading curvature. As a calibration of the time increment Δt, the calculation results show that the smaller the Δt value is, the influence on the predictions can be ignored. In other words, the predictions of penetration depth can be independent of the Δt value and thus reflect the objective essence of loading process. By taking Δt value as 0.001s for three materials with different constitutive properties, the P–h curves under load and displacement control manners are compared, and excellent agreement is found. The proposed method provides a new and elegant way to realize equivalent load control by displacement control of the indenter for nanoindentation simulations.

Equivalence of nanoindentations by the load and displacement controlled manners


Purpose
The purpose of this paper is to analyze and compare the mechanical properties of sintered nanosilver with different porosities at both the mesoscopic and macroscopic scales and to conduct a multiscale analysis of the porosity effect on the mechanical properties of sintered nanosilver.


Design/methodology/approach
This paper establishes a mesoscopic model for the uniaxial tension of sintered nanosilver and a macroscopic model for chips containing sintered silver layers. Using the finite element method, combined with crystal plasticity theory and unified creep plasticity theory, a multiscale analysis is conducted for the mechanical properties of sintered nanosilver. First, stress distribution characteristics under uniaxial tensile loading for different porosities in sintered nanosilver polycrystal models are analyzed at the mesoscopic scale. Second, at the macroscopic scale, the mechanical performance of sintered nanosilver layers with varying porosities in high-power chip models under cyclic loading is analyzed. Finally, the porosity influence on the damage evolution in sintered nanosilver is summarized, and simulations are conducted to explore the evolution of damage parameters in sintered nanosilver under different porosities.


Findings
In the mesoscopic model, the presence of mesoscale voids affects the stress distribution in sintered nanosilver subjected to tensile loading. Sintered nanosilver with lower porosity exhibits higher tensile strength. In the macroscopic model, sintered nanosilver layers with lower porosity correspond to a more uniform stress distribution, whereas higher porosity leads to faster accumulation of plastic strain in the sintered layer. During chip packaging processes, improving processes to reduce the porosity of sintered layers can delay the initiation of damage and the propagation of cracks in sintered nanosilver.


Practical implications
During chip packaging processes, improving processes to reduce the porosity of sintered layers can delay the initiation of damage and the propagation of cracks in sintered nanosilver.


Originality/value
This paper innovatively uses a mesoscopic crystal plasticity constitutive model and a macroscopic unified creep plasticity constitutive model to analyze the mechanical behavior of sintered nanosilver with different porosities. It comprehensively investigates and explains the influence of porosity on the mechanical performance of sintered nanosilver across multiple scales.


Exploring porosity effects of on mechanical behavior of sintered nanosilver for double-sided cooling packaging of high-power devices: a multiscale modeling

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Papers

Meso-scale low-cycle fatigue damage of polycrystalline nickel-based alloy by crystal plasticity finite element method

Meso-scale crystal plasticity modeling of sintered silver nanoparticles in typical interconnected structures

Equivalence of nanoindentations by the load and displacement controlled manners

Exploring porosity effects of on mechanical behavior of sintered nanosilver for double-sided cooling packaging of high-power devices: a multiscale modeling