Hierarchical Biomechanics: Concepts, Bone as Prominent Example, and Perspectives Beyond

Effect of aggregate shapes on local fields in 3D mesoscale simulations of the concrete creep behavior

A plurality of articles discussing combined effects of acoustic high-pressure and heat caused by acoustic vibration on biological tissues and cells has been published. Herein, we contribute the article describing the behavior of living human skin cells when separately applying the pressure and the heat to them. First, for finding the heat effect, we located a container including living human skin cells and a culturing medium on the X-Y stage equipped with the heating plate with temperature controller of the Scanning Acoustic Microscope (SAM). Then, we gradually increased temperature of the culturing medium, and carried out in-situ observation. Second, for finding the acoustic high-power effect, we provided the pressure using high power ultrasonic pulses generated by a laser induced ultrasonic shock wave system to the cells, wherein the pressures caused by the pulses were measured by a hydrophone, and wherein temperature was monitored by thermocouples. The cells were observed with the SAM just after giving the impact. The difference between phenomena indicating cellular insult and injury (e.g., shrinkage or lift-off) were clearly visualized by the SAM with frequency at 1.0 GHz.

Caused by its superior performance regarding bandwidth, power loss and form factors compound semiconductors like GaN or SiC recently moved into the interest of the semiconductor industry, particularly for applications in the high power segment. These improved performance parameters go along with increased power densities and thus, require a specifically optimized thermal concept of the packaging. Ag-sintering as die-attach process has been widely accepted as a promising alternative to soldering techniques with respect to thermal conductance. However, the thermal and the mechanical behavior of the sinter layer is influenced by its composition on the micro -and the macroscopic scale with respect to the presence of voids, inclusions and delamination but also the fractional content of porosity. Scanning acoustic microscopy (SAM) uses acoustic waves that interact with the mechanical properties of the sample materials and is thus, widely established for the non-destructive detection of voids, inclusions and delamination in microelectronic components. The current paper investigates the potential of SAM as a method for the assessment and characterization of the porosity in sintered Ag layers targeting the die-attach technology for novel power semiconductor devices.

Location resolved transient thermal analysis to investigate crack growth in solder joints

Diffusion bonds produced in microduplex titanium and stainless steel sheet materials for various bonding conditions have been evaluated using a range of techniques. These include light and scanning electron microscopy (SEM), scanning acoustic microscopy (SAM) and compressive lap shear testing. The potential of other procedures such as ultrasonic inspection and resistivity measurement are also discussed. For imperfect bonds, the bond line in titanium alloys consists of clearly defined interfacial voids separated by metallurgically sound bonded regions, while the unbonded regions in stainless steel often consist of long flat voids in which the opposing surfaces have contacted but not bonded. It was observed that light microscopy and SEM observations provide a convenient and reliable method for the assessment of the bond quality, and in the case of titanium alloys it is possible to obtain quantitative data on the extent of bonding. High frequency SAM also proved to be an effective procedure for qualitative assessment. A linear relationship between the fraction of parent metal strength achieved and bonded area fraction as determined by metallography was observed for titanium alloys.

This investigation describes a part of the ongoing activities in the advanced semiconductor materials and packaging collaboration with SPEL Semiconductor Ltd. The aim of the investigation was to generate 3D models of the IC packages, 8L and 12L (8 pin and 12 pin configurations) micro dual leadless moulded packages (μDLMP) in pro-engineer and conduct the performance analysis using the finite element software ANSYS™. Reliability plays a major role at every stage in the manufacturing, testing and use of integrated circuit packages. The influence of operating voltages and joule heating on the mechanical reliability of ICs was also investigated. Die shear tests were conducted on the ICs and the shear strength compared with the values obtained from the finite element results. Thermal tests were carried out on the ICs that were later inspected under a scanning acoustic microscope (SAM) for delaminations arising from hygrothermal stresses. Finally, the results of the electro-hygrothermo-mechanical analyses were analysed and presented at the maximum operating temperature (MOT) that highlight the overall static reliability of the ICs with acceptable factors of safety.

A finite element (FE) model has been developed based upon the recently measured micro-scale morphological, chemical and mechanical properties of dentin-adhesive (d-a) interfaces using confocal Raman microspectroscopy and scanning acoustic microscopy (SAM). The results computed from this FE model indicated that the stress distributions and concentrations are affected by the micro-scale elastic properties of various phases composing the d-a interface. However, these computations were performed assuming isotropic material properties for the d-a interface. The d-a interface components, such as the peritubular and intertubular dentin, the partially demineralized dentin and the so-called "hybrid layer" adhesive-collagen composite, are probably anisotropic. In this paper, the FE model is extended to account for the probable anisotropic properties of these d-a interface phases. A parametric study is performed to study the effect of anisotropy on the micromechanical stress distributions in the hybrid layer and the peritubular dentin phases of the d-a interface. It is found that the anisotropy of the phases affects the region and extent of stress concentration as well as the location of the maximum stress concentrations. Thus, the anisotropy of the phases could effect the probable location of failure initiation, whether in the peritubular region or in the hybrid layer.

In pressure vessel and pipe inspection, ultrasonic nondestructive evaluation plays a pivotal role in both in-situ and laboratory examinations. Scanning acoustic microscopy (SAM) has been a well-recognized laboratory tool for both visualization and quantitative evaluation of pressure vessel and piping materials at the microscale since its invention in 1974. While there have been multiple advances in SAM over the past four decades, some issues still remain to be addressed. First, the measurement speed is limited by the mechanical movement of the acoustic lens and the sample stage. Second, a single-element transducer with an acoustic lens forms a predetermined beam pattern for a fixed focal length and incident angle, thereby limiting control of the inspection beam. Here, we propose to develop a phased-array probe as an alternative to overcome these issues. Preliminary studies to design a practical high-frequency phased-array acoustic microscope probe were explored. A linear phased-array, comprising 32 elements and operating at 5 MHz, was modeled using PZFlex, a finite element method software. This phased-array system was characterized in terms of electrical input impedance response, pulse-echo and impulse response, surface displacement profiles, mode shapes, and beam profiles. Details of the construction of the model and the results are presented in this paper. Development of a phased-array acoustic microscope probe will significantly enhance scanning acoustic microscopy techniques for detecting surface and subsurface defects and microstructural changes in laboratory samples of pressure vessel and piping materials.

Scanning acoustic microscopy (SAM) was equipped to assess the acoustic properties of normal and atherosclerotic coronary arteries. The SAM image in the atherosclerotic lesion clearly demonstrated that the sound speed was higher than that in the normal intima, and that the variation of elasticity was found within the fibrous cap of the plaque. Young's elastic modulus of each region was calculated and the finite element analysis was applied to derive the stress distribution in these arterial walls. In a case of normal coronary artery, the stress was dominant in the intima and the distribution was rather homogeneous and in a case of atherosclerosis, high stress was concentrated to the relatively soft lesion in the fibrous cap overlying lipid pool. SAM provides information on the physical properties, which cannot be obtained by the optical microscope. The results would help in understanding the pathological features of atherosclerosis.

Computational tools are often needed to model the complex behavior of biological tissues and cells when they are represented as mixtures of multiple neutral or charged constituents. This study presents the formulation of a finite element modeling framework for describing multiphasic materials in the open-source finite element software febio.1 Multiphasic materials may consist of a charged porous solid matrix, a solvent, and any number of neutral or charged solutes. This formulation proposes novel approaches for addressing several challenges posed by the finite element analysis of such complex materials: The exclusion of solutes from a fraction of the pore space due to steric volume and short-range electrostatic effects is modeled by a solubility factor, whose dependence on solid matrix deformation and solute concentrations may be described by user-defined constitutive relations. These solute exclusion mechanisms combine with long-range electrostatic interactions into a partition coefficient for each solute whose value is dependent upon the evaluation of the electric potential from the electroneutrality condition. It is shown that this electroneutrality condition reduces to a polynomial equation with only one valid root for the electric potential, regardless of the number and valence of charged solutes in the mixture. The equation of charge conservation is enforced as a constraint within the equation of mass balance for each solute, producing a natural boundary condition for solute fluxes that facilitates the prescription of electric current density on a boundary. It is also shown that electrical grounding is necessary to produce numerical stability in analyses where all the boundaries of a multiphasic material are impermeable to ions. Several verification problems are presented that demonstrate the ability of the code to reproduce known or newly derived solutions: (1) the Kedem-Katchalsky model for osmotic loading of a cell; (2) Donnan osmotic swelling of a charged hydrated tissue; and (3) current flow in an electrolyte. Furthermore, the code is used to generate novel theoretical predictions of known experimental findings in biological tissues: (1) current-generated stress in articular cartilage and (2) the influence of salt cation charge number on the cartilage creep response. This generalized finite element framework for multiphasic materials makes it possible to model the mechanoelectrochemical behavior of biological tissues and cells and sets the stage for the future analysis of reactive mixtures to account for growth and remodeling.

In this paper, an Ultrasonic Non-Destructive Test (NDT-UT) has been carried out on steel using the Simulink-Matlab Mathematica computation method. This study aims to analyze the NDT-UT output signal for material defect detection using secondary data as the first sample. The sample is then analyzed using the Fast Fourier Transform (FFT) method to produce a spectrum waveform and image thermography. It can be seen that there is a decrease in signal height from 1 a.u to 0.55 a.u. The first sample waveforms were used to analyze the second sample, third sample, and fourth sample, and all the samples had different defects. The results of the sample analysis are in the form of a thermographic image that shows the temperature level based on the distribution of red (R), green (G), and blue (B) images on the sample surface. The NDT-UT output signal produces a sinusoidal wave similar to the results of the Simulink-Matlab modeling analysis on the initial input echoes and the back wall, with a percentage inequality of 10%. Then validated the sinusoidal signal from the NDT-UT which gave a percentage of inequality between 0% – 42%. More complex or irregular defects result in a larger percentage or vice versa.

This paper gives insight into the influences of spatially varying material properties on the non-linear finite element modeling of the rectangular and square-shaped floor slabs. Modeling the properties of the concrete using spatially distributed properties instead of using constant properties is more realistic. We analyzed the influence of probabilistic concrete property modeling on the development of cracks in floor slabs. A concrete floor subjected to a shrinkage load was analyzed using the material model with randomly distributed compressive strength. Consequently, the tensile strength and elastic modulus were also randomly distributed. The concrete properties were defined by the random field generator that uses the Fast Fourier Transformation method and the guidelines given by the Joint Committee on Structural Safety Probabilistic Model Code. The obtained results are compared with the values from modeling with constant concrete properties. The comparison shows that the crack development in the slabs with and without varying material properties is statistically significantly different.

Stress-driven nonlocal homogenization method for cellular structures

Abstract: The biomechanics of human head neck system could be better understood by creating finite element models of the same that accurately represents most of the components of head and neck. The initial geometry of the human head and neck was obtained using the computer tomography scans. The finite element models are created from these computed tomography scans and are further undergone through the various analysis procedures of finite element analysis. Thus, the developed finite element head neck models could be studied for various kinds of impacts acting on the head neck system during the time of any vehicle collisions, spaceflights etc. The development of these models and the various impact studies helps in the safety of the people. In this paper the concept of Finite element method, application of finite element method in biomechanics and various steps involved in this method are discussed in detail. Similarly, the finite element models of head and neck system developed by various researchers are also considered.

A Model of Fibroblast Motility on Substrates with Different Rigidities