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Various novel 3D micro machining technologies were researched and developed for silicon micro mechanical system fabrication. Micro EDM is one of them. The material removal mechanism is thermal sparking erosion and is completely independent with regards to the crystalline orientation of silicon, therefore there is no orientation constraint in processing the complex 3D geometry of silicon wafers. As thermal sparking implied, the process features local area high temperature melting and evaporating, and this characteristic has an adverse side-effect on the sparked surface integrity. One important concern is the generation of micro cracks, which would provide an adverse effect on the fatigue life of the micro feature element made of silicon. For this consideration, in this paper, with the experiment and SEM picture analysis approach, the author explored the micro crack generation characteristics on mono crystalline silicon wafers under micro EDM with available sparking energies and on the different crystal orientation surface machining. The generation of micro cracking is not only related with the sparking energy but also related with the crystalline orientation. The {100} orientation is the strongest surface to resist crack generation. For a strong-doped P type silicon wafer, there exists a maximum crack energy threshold. If single sparking energy is over this threshold, micro cracks unavoidably would be generated on any orientation surface. Two types of chemical etching post processes that can remove cracks on sparked surfaces are also tested and discussed.

The article presents the results of the impact of laser welding parameters on defect occurrence in the welded seam of the Ni-based heat-resistant alloy Kh45VMTYuBR applied for the manufacture of gas-turbine engines. On the basis of the research the authors conduct the analysis of dimensions as well as the number of pores and micro-cracks in the welded seam. The paper provides the recommendations on the selection of the laser welding mode for the heat-resistant alloy to reduce defect occurrence in a welding seam.

The powder mixed electrical discharge machining, also called PMEDM, is gaining much attention, because it is demonstrated as a good solution for enhancing productivity and surface integrity. In thi...

The tool material properties are essential key factors for the enhancement of electro discharge machining performance mainly, resistance to the wear of tool, removal of material from workpiece, and...

The characterization of micro cracks on metal surface plays an important role in the process of manufacturing and using, which has attracted a lot of attention. This is mainly due to the fact that the size of defects is smaller and the depth of defects is difficult to predict compared with metal materials with larger plane, which is still challenging. In order to solve this problem, this paper proposes a characterization method of surface defects based on reflective laser thermography, and designs a laser heating nondestructive testing system based on reflection. The system includes a semiconductor laser to heat the surface of metal cracks, and an infrared imager to record changes in the temperature field of the metal surface. In the process of data analysis, an Otsu adaptive threshold segmentation method is selected to quantify the defect size, which can control the quantification accuracy of defect size within 25%. A derivative analysis method is proposed to quantify the depth of defects, which can control the depth quantification accuracy of tiny defects within 7%.

Crystalline admixtures embedded in concrete may react in the presence of water and generate thin crystals able to fill pores, capillaries and micro-cracks. Once the concrete has dried, the crystalline chemicals sit dormant until another dose of water starts the crystallization again. The research aims to analyses the early age self-sealing effect of a crystalline admixture at a dosage rate of 1–3% of the cement mass. Specimens made with two types of gravel were pre-loaded with three-point bending to up to 90% of the ultimate capacity, and conditioned through wet–dry cycles. Micro-crack closure was measured with a microscope after pre-loading, and after 1 day, 4 days, 8 days, 14 days and 20 days of wet–dry exposure. The results show that an admixture content of 3% achieves the best early self-sealing performance. These results are also confirmed by probabilistic analyses, which also emphasize the self-sealing potential of lower ICW contents.

A multi-level and multi-site local mesh refinement method is developed to calculate the local responses of 2D problems with multi-site microstructures. The optimal mesh density is employed for all ...

The alkali aggregate reaction (AAR) about the aggregate marked with W1# was studied by using of four kinds of methods, including accelerated mortar bar test (AMBT), mortar bar length test (MBLT), concrete prism method (CPM) and rock column method (RCM). AMBT showed that the expansion ratio of the specimens at 14 days was 0.200%, and the expansion ratio at 28 days was 0.404%; MBLT showed that the expansion ratio at 3 months was higher than 0.050%, and the expansion ratio at 6 months was higher than 0.100%; CPM showed that the expansion ratio at 39 weeks was higher than 0.040%. These studies above indicated that W1# aggregate was the aggregate with potential alkali-silica activity. RCM tests showed that the aggregate doesn’t have potential alkali-carbonate activity. The inhibiting experiments showed that the expansion ratio at 14 days and 28 days were less than 0.10% by adding more than 45% (Wt/%) limestone powder or adding 15% (Wt/%) fly ash, meanwhile, the expansion ratio at 14 days and 28 days were all less than 0.10% after adding 15% (Wt/%) limestone powder and 30% (Wt/%) fly ash or adding 25% (Wt/%) limestone powder and 25% (Wt/%) fly ash, respectively. Mesh structures were formed by the hydration products in the micro structure, and no micro cracks and the white flocculent products could be observed inside and outside of the samples. All the results above confirm that AAR of the aggregate was inhibited effectively, and it will play the useful role in AAR research.

28th International Workshop on Computational Mechanics of Materials (IWCMM) -- SEP 10-12, 2018 -- Univ Strathclyde, Technol & Innovat Ctr, Glasgow, SCOTLAND Basoglu, Muhammed Fatih/0000-0002-6994-8225; Kefal, Adnan/0000-0002-4139-999X; Zerin, Zihni/0000-0001-7906-8136 WOS: 000464128700004 The critical effect of micro level defects should be examined at macro level to better understand the fracture behaviors of engineering materials. This study investigates the branching and deflecting behavior of a macro (main) crack in presence of multiple number of micro-cracks at the vicinity of the crack tip. For this purpose, a non-local continuum theory, known as Peridynamics (PD), is utilized based on the original set of bond-based PD equations. The main advantage of using PD is its characteristic superiorities on the modelling of dynamical fracture. Various example problems with inclined-linear and/or curvilinear micro-crack clusters are solved through the implementation of different numerical models to better understand the micro-crack toughening mechanisms. After validating the PD implementation with a benchmark case, several combinations of multiple micro-cracks with various locations are considered. To capture complex forms of crack branches, the positions of micro-cracks are designated to follow an encircling and spreading patterns at the vicinity of the main-crack tip. Hence, more internal energy is dissipated through the generation of new crack surfaces such that the main-crack deflects along a more twisting path. It has been observed that depending on the amount of dissipated energy, the propagation speed of main-crack alters. Also, it has been demonstrated that encircling potential crack propagation regions with micro-cracks provides an augmented toughness to the brittle materials. Overall, the efficiency and robustness of the PD theory are revealed for simulating crack propagation in brittle materials.

The time reversal (TR) method is applied to the localisation of microcrack based on the vibro-acoustic modulation (VAM) which is one of the effective non-linear ultrasonic testing approache...

The surface properties of machine components are enhanced by surface modification. The workpiece surface can be modified using electro discharge machining (EDM) process. In this paper, mild steel w...

In the present investigation, tribological behaviour of the hot extruded Al–Cu–Mg–Ag (matrix) alloy and the effect of Ti and TiB2 addition in matrix alloy have been studied. Hot extrusion was introduced to eliminate cast defects like porosity, voids and micro cracks. Addition of Ti and TiB2 particles increased the hardness of the matrix by grain refinement and dispersion hardening, respectively. It has been observed that the increase in hardness had significantly improved the wear resistance of the material. Detail study of the wear surfaces and debris were carried out to understand the wear mechanism of the samples. It revealed a complex mechanism of micro-cutting, plastic deformation, abrasion and delamination of the wear samples.

International audience; This paper shows the complementarity of two nonlinear ultrasonic imaging methods to characterize closed macro cracks in concrete. A time reversal mirror is used to locally probe and image the nonlinearity of a cracked region. Two nonlinear parameters are extracted to map the cracked region. The image obtained using the first parameter relates the harmonic generation due to the contact and frictional behaviors at the crack lips, correlated with vibro-thermography imaging of the same crack. The image obtained using the second parameter is based on the conditioning of the material induced by distributed micro cracks arising from the fracture process zone. These results show a great potential for characterization of fracture processes in concrete, with the possibility to uncouple the effects of the crack itself from surrounding distributed micro damage.

Enhancing and characterization of self-healing ability of ultra high performance concrete (UHPC) is the main aim of this study. The self-healing mechanisms of macro/micro cracks were investigated through different techniques with some novel procedures. Two different mix designs have been considered to increase the amount of unreacted particles in the matrix. In spite of the positive effect of supplementary cementitious materials (SCM) on self-healing ability of UHPC, it was observed that the detected self-healing ratios depend on critical parameters such as damage type/level and the methods used to verify the phenomenon of self-healing. Depending on the composition of the UHPC mixtures, the age of specimens and the assessing method, up to 70-76% recoveries were obtained in the compressive strength and permeability of specimens pre-loaded up to -400% of their corresponding compressive strength. In addition, up to 88-100% crack sealing was observed in the pre-cracked UHPC specimens assessed via various methods. (C) 2021 Elsevier Ltd. All rights reserved.

Chloride penetration resistance of concrete is one of the key parameters for the durability design of reinforced concrete structures located in chloride-bearing environments. In all the current available durability models, service life is evaluated considering concrete in uncracked conditions, which is rarely found in practice. This work investigates chloride penetration resistance of concrete in uncracked and micro-cracked configurations, evaluated in terms of chloride migration coefficient through non-steady state migration test (Rapid Chloride Migration test). Prismatic specimens were manufactured considering six different concrete types and two different times of curing. In micro-cracked configuration, cracks were obtained with a specifically developed loading procedure. Micro-cracks were characterized at the end of the exposure test, in terms of crack width at the exposed surface and crack depth. Results showed that cracks were 5–70 μm wide and up to 40 mm deep, always causing an increase in chloride penetration, that should be evaluated considering both crack width and crack depth, with respect to sound conditions. The effects on the chloride penetration seemed to be more pronounced on the more impervious concretes.

Ultrafine β grain structures with recrystallized morphologies were fabricated by severe plastic deformation and subsequent annealing in Ti-10Mo-8 V-1Fe-3.5Al alloy. The minimum mean β grain size of 480 nm was obtained for the first time as a recrystallized structure in Ti alloys. Precipitation behavior of α in subsequent aging significantly changed with decreasing the recrystallized β grain size. Both tensile strength and total ductility of the aged Ti-alloy were increased by the β grain refinement. Tensile strength of 1.6 GPa and total elongation of 9.1% were achieved in the aged specimen having the prior β grain size of 480 nm, which was attributed to its finer and more homogeneous precipitated microstructure having a mixture of nanoscale thin-plate α and globular α without side α plates along β grain boundaries.

This paper microscopically investigated progressive failure characteristics of brittle rock under high-strain-rate compression using the bonded particle model (BPM). We considered the intact sample and the flawed sample loaded by split Hopkinson pressure bar respectively. Results showed that the progressive failure characteristics of the brittle rock highly depended on the strain rate. The intact sample first experienced in microcracking, then crack coalescing, and finally splitting into fragments. The total number of the micro cracks, the proportion of the shear cracks, the number of fragments and the strain at the peak stress all increased with the increasing strain rate. Also, a transition existed for the failure of the brittle rock from brittleness to ductility as the strain rate increased. For the flawed sample, the microcracking initiation position and the types of the formed macro cracks were influenced by the flaw angle in the initial stage. However, propagation of these early-formed macro cracks were prohibited in the later stages. New micro cracks were produced and then coalesced into diagonal macro cracks which could all form &lsquo, X&rsquo, shape failure configuration regardless of the incline angle of the flaw. We explored micromechanics on progressive failure characteristics of the brittle rock under dynamic loads.

Fatigue micro-cracking behavior in pre-corroded AA7075-T7651 is analyzed by in-situ scanning electron microscopy (SEM) observation and SEM-based fractography. The experimental results show that (i) fatigue microcracks nucleated mainly from inclusions at the specimen notch and from corrosion pits on the specimen surface, (ii) pre-corrosion severity degree and maximum stress level significantly affected the extent and time of microcrack initiation. Corrosion pits are shown to play a crucial role in fatigue micro-crack propagation, due to crack deflection (light corrosion) and crack coalescence (severe corrosion). The growth rate of minor cracks was suppressed by pre-dominant rapid propagation of the main crack. This research was supported by the National Natural Science Foundation of China (NSFC, Grant Nos. 11972364, 11502285 and 51971242), the Science Foundation Ireland (SFI, Grant No. 14/IA/2604) and the Fundamental Research Funds for the Central Universities (FRFCU, Grant No. 3122014H006). peer-reviewed 2022-04-18

Pore pressure and thermal dehydration of concrete are two major factors which affect the spalling of concrete at high temperatures. Thermal dehydration can cause deterioration of concrete properties and promote the development of micro cracks in the skeleton of concrete. Pore pressure will also be influenced by dehydration when the hydrated water enters the micro pores. In the current study, a framework of elastoplastic damage constitutive model is developed to described the mechanical behaviour of concrete and pore pressure at high temperatures. Both load induced damage and thermal dehydrated damage are considered. The thermal dehydrated damage is temperature related, which reflects the impact of temperature on concrete properties. A model of pore pressure is developed by considering the influence of thermal dehydration and damage related permeability. The pore pressure field associated with vapor, liquid water and dry air is predicted and compared with experimental results.

In recent years, potential induced degradation (PID) has been a topic of interest to scientists because of its significant impact on performance deterioration of solar cells. Research has shown that the major cause of PID defects for p-type Si solar cells is sodium (Na) ion migration from the soda-lime glass through the encapsulation layer into the solar cell. However, limited scientific investigations have been done on the influence and mechanism of Na ion decorated micro-cracks on the evolution of PID. In this work, Na ion decoration in micro-cracks as the important mechanism causing PID in p-type crystalline Si solar cells is presented and discussed in detail. Furthermore, a model of PID mechanism due to micro-cracks is proposed.

Composites are extensively using in modern industry (aircraft and automobile manufacturing, construction, etc.). Nowadays high-strength and lightweight composite materials, such as FRPs, exhibit elastic and strength anisotropy and deform nonlinearly at high stresses. Also, such materials have small enough failure strain in comparison with metals, and they are drastically more expensive than steel and aluminum alloys. The most important task in the design of structures made of composite materials is the minimization of its weight without loss of strength properties. We presented the method for modeling a UD FRP with randomly arranged fibers at the micro-and meso-level. These two approaches were compared on the problem of the composite panel tension. The selection of the mesomodel mechanical characteristics was based on data of the micro-level model. In the mesomodel, the damage accumulation of middle layer (90° layer) was simulated using the Stochastic Failure criterion (random Mott scatter of layer strength). The calculated curves and data, obtained in micro-and mesomodels, correlate well with each other.

Damage and fracture of quasi-brittle materials are non-reversible processes of micro-defects and micro-cracks, often accompanied by a strip of micro-crack damage along the end of the macro-crack or gap. In this work, the micro-crack damage parameters in the strip are calculated, and a mechanics model is proposed to analyze the relation between deformation and force. The mechanics parameters are also determined using meso-mechanics homogenization of the damage zone of the micro-crack strip. Then, calculations of the deformation and stress in the damage strip are introduced, and the damage factor is estimated using a cohesive crack model. Finally, the relationship between the micro-crack and macro-fracture zone is correlated to electron microscopy data of a cast iron specimen and numerical results. For the damage factor, damage density, and geometrical factors of micro-cracks, the meso-mechanics scale is correlated to macro-mechanics in the damage fracture process zone by combining the homogenization method and cohesive crack model of nonlinear fracture.

The solution of an infinite plane containing an arbitrarily located micro-crack and a kinked macro-crack is presented based on the distributed dislocation technique (DDT). The stress field, the plastic zone of the macro-crack tip (PZ) and the stress intensity factors at the macro-crack tip (SIFs) are obtained. The influence of the micro-crack on the kinked macro-crack is investigated. The results show the effect of the micro-crack on SIFs increases with the micro-crack length increasing, the distance d decreasing and the micro-crack angle decreasing. The micro-crack has an amplifying effect on mode I SIF at about - 80 ° θ 60 ° , while it has a shielding effect at about - 90 ° θ - 80 ° and 60 ° θ 90 ° . The micro-crack has an amplifying effect on mode II SIF at about - 90 ° θ 20 ° , while it has a shielding effect at about 20 ° θ 90 ° . The micro-crack ahead of PZ has a little amplifying effect on PZ. As the micro-crack is close to the macro-crack tip, plastic zones of the micro-crack tip and macro-crack tip will join together. PZ is split into two pieces by the micro-crack located in PZ. The micro-crack behind PZ has no effect on PZ. These results are helpful to analyze the fracture or fatigue behaviors of materials.

This research aims to investigate micro-crack on a failed for helical gear transmission which was to adjust the engine to increased horsepower. The helical gears made are from chromium steel JIS-SCr 420. The spectrophotometer test machine was used to detect chemical composition, Mechanical properties were evaluated by Vickers hardness and microstructural analysis with an optical microscope, which the crack of the surface layer and energy dispersive spectroscopy using a scanning electron microscope. The results showed that the fracture characteristic of the helical gear’s surface was expected to beach marks and break away. It can be seen that the mixing failure area of oxide inclusion with carbide surrounding before the liquid state of material will be solidified which caused the failure cause of this helical gear. The summary analysis results can be accorded with the assumption of this research and which help prolong service life of the component.

Micro damage evolution in chemical corroded limestone samples subjected to cyclic loads is investigated using Nuclear Magnetic Resonance (NMR) system. Based on the experimental data of Magnetic Resonance Imaging (MRI), T2 values and porosity, the micro damage evolution process is visualized and analyzed. It is found that the porosity and micro cracking of the corroded limestone samples increase with the cyclic loading, and the micro damage evolution process consists of three distinct stages: micro crack emergence stage, micro damage development stage and damage development accelerated stage. Chemical erosion is found to have a significant influence on the propagation of micro cracks and accelerate the damage development of the limestone samples under cyclic loading. With the same number of load cycles, the chemical corroded samples always have lower peak strength than that of the water softened samples. Before the inflection point in the micro damage-loading cycles curve, the main damage is caused by new micro cracks increase inside the limestone; while after this point, the new micro crack emergence is being restrained, and the existed micro cracks connect into rupture bands. A damage model is finally proposed to quantify the damage evolution of the chemical corroded rocks subjected to cyclic loads.

This paper investigated the relationship between crystallographic-orientation and micro-cracks of Ti-47Al-2Cr-2Nb alloy. Results show that the crystallographic-orientation is adverse in the nearly γ microstructure and becomes advantageous in the fully lamellar microstructure. Therefore, micro-cracks largely generate in the nearly γ microstructure and much decrease in the fully lamellar microstructure.

This paper presents the results of a microscopic investigation of fractured Storz type fire hose couplings. It is part of the authors’ previous investigations on the failure mechanisms of this type of couplings. The investigations were performed using optical and scanning electron microscopy with Field Emission Gun (FED) and X-ray Energy Dispersive Spectrometer (EDS). It is shown that the AlSi5Cu1Mg casting alloy, used for the fabrication of these couplings, presents a normal microstructure. Thus, the nucleation and growth of micro-cracks in the investigated couplings are not related to the alloy’s microstructural defects and must be generated by a different process.

The behavior of the new AA2198-T8 high strength aluminum alloy during tensile and very high cycle fatigue (VHCF) tests is studied. The results of the tensile tests show that the alloy in this heat treatment state has excellent mechanical properties compared with the same alloy with other heat treatment conditions and the 2024 and 7075 conventional aluminum alloys. The VHCF tests show a fatigue life plateau with the fatigue life reaching 109 cycles under a stress amplitude of 200 MPa, suggesting the existence of an endurance limit. Two different crack initiation modes are observed under scanning electron microscopy (SEM). Cracks tend to initiate from the interior of the specimen when fatigue life is in the VHCF regime. The interior crack initiation mode has a characteristic of a fish-eye, at the center of which is a white rough area (WRA) where the original micro-crack initiates. The thermo-mechanical process during ultrasonic fatigue is also studied. Quantitative analyses on micro-crack initiation and propagation show that the threshold stress intensity factor for stable micro-crack propagation is 1.66 MPa m1/2, and the threshold stress intensity factor for unstable macro-crack propagation is 3.17 MPa m1/2. Finally, analyses based on the Paris-Hertzberg law suggest that the micro-crack initiation stage likely consumes most of the fatigue life. The analyses do not apply to fatigue lives less than 106 cycles. The prediction of fatigue life is confirmed by the analyses of the thermo-mechanical process.

The objective of this study is to analyze the behavior of repairing agent of microcapsule in asphalt micro crack based on molecular dynamics simulation. Based on the molecular dynamics software Material Studio 7.0 (MS), a four-fraction molecular model of asphalt and a molecular model of repairing agent of the microcapsule core material were constructed. Based on this, the micro crack models with and without repairing agents in asphalt were constructed, and the dynamics simulation calculations were carried out. The density and energy of the repairing agent moving in the micro crack after being released from microcapsule were studied, as well as the diffusion coefficient of molecules of the two models. The shear modulus of the models before and after crack repairing were analyzed. Additionally, the effects of temperature and molecular type on crack repairing were also analyzed. The results indicated that crack repairing was a process of mutual diffusion between the repairing agent and asphalt under the main driving force of potential energy. The repairing agent in the cracks accelerated the diffusion of the asphalt molecules to promote crack repairing rate; Crack repairing speed and temperature were positively correlated, that is, the repair rate increases with the increase of temperature. After the crack repair, the shear modulus of the models with and without repairing agent increased by 228.57% and 111.11%, respectively, indicating that the repairing agent also accelerated the mechanical property recovery of the crack model. The light and long chain-like small molecule type repairing agent could more promote the self-repairing process, and be more suitable for use as a core material repairing agent of microcapsules.

Single-crystal nickel-rich cathode materials (SC-NRCMs) are the most promising candidates for next-generation power batteries which enable longer driving range and reliable safety. In this review, the outstanding advantages of SC-NRCMs are discussed systematically in aspects of structural and thermal stabilities. Particularly, the intergranular-crack-free morphology exhibits superior cycling performance and negligible parasitic reactions even under severe conditions. Besides, various synthetic methods are summarized and the relation between precursor, sintering process, and final single-crystal products are revealed, providing a full view of synthetic methods. Then, challenges of SC-NRCMs in fields of kinetics of lithium diffusion and the one particularly occurred at high voltage (intragranular cracks and aggravated parasitic reactions) are discussed. The corresponding mechanism and modifications are also referred. Through this review, it is aimed to highlight the magical morphology of SC-NRCMs for application perspective and provide a reference for following researchers.

This paper reviews the types of bacteria used in concrete and the ways it can be applied as a healing agents. This paper also gives a brief description of the various properties of concrete which vary with the addition of bacteria. Micro-cracks are inherently present in concrete. This causes degradation of concrete leading to ingress of deleterious substances into concrete, resulting in deterioration of structures. Due to this concrete needs to be rehabilitated. To surmount these situations self-healing techniques are adopted. By the addition of urease engendering bacteria along with calcium source results in calcite precipitation in concrete. Bio-mineralization techniques give promising results in sealing the micro-cracks in concrete. The freshly composed micro-cracks can be sealed up by perpetual hydration process in concrete. The ureolytic bacteria which include Bacillus Pasteurii, Bacillus Subtilis which can engender urea are integrated along with the calcium source to seal the freshly composed micro cracks by CaCO3 precipitation. For the amelioration of pore structure in concrete, the bacterial concentrations were optimized for better results. The literature shows that Encapsulation method will give better results than direct application method and also shows that the use of bacteria can increase the strength and durability properties of concrete.

Environmentally-assisted cracking (EAC) of structural metal materials occurs by initiation and coalescence of micro cracks, subcritical crack propagation and multiple large crack formation or final failure under combination of material, stress and corrosive environment. EAC is an important issue in sour oil and gas fields due to presence of different operational conditions; therefore, it can influence on the performance and lifetime of materials widely carried out in the oil and gas industries. Numerous standard mathematical models have been established based on the mechanisms leading to the EAC pertaining failures. The aim of this research is introducing the development of the simulating models basis for the quantitative prediction and qualitative diagnostics of the cracking incidence and failure under the impact of stresses and sour environments. The comparative aspects of the mentioned simulation models were discussed through diagrams, tables and scientific figures.

The correlation between intermetallic compound (IMC) and interface bonding state of the pure Al/08Al steel clad plate after 645°C/1h diffusion annealing was studied using the SEM. The results indicated that after 645°C/1h diffusion annealing for the pure Al/08Al steel clad plate, the IMC grew continuously along the interface with the thickness of 2-6 μm, while, at some regions grew abnormally with the thickness up to 10-30 μm. Moreover, some intrinsic defects at the interface, such as voids in the abnormally grown IMC and micro cracks along the interface were observed. The voids were possibly caused by huge difference of Al and Fe in diffusion coefficient, which is known as Kirkendall effect. On the other hand, the micro cracks could be attributed to the thermal stress during the cooling process because of larger difference of thermal expansion rate between Al and Al-Fe IMC. The intrinsic defects at the interface of Al/Steel could supply a novel way to correlate the morphology of IMC and interface bonding strength.

This paper is focused on prediction of nitinol stents lifetime. Stents have been tested before and after mechanical loading. Corrosion tests of mechanically loaded specimens indicated impairment of corrosion resistance and SEM observation confirmed presence of micro cracks in surface oxide layer created during heat treatment. Electrochemical impedance spectroscopy and potentiodynamic polarization in physiological solution was used for these particular experiments. Corrosion rate and other parameters have been used for calculation of released nickel ions weight and prediction of application lifetime.

In engineering practice, failures due to fatigue cracks in metallic structures have always been difficult to predict. In our study, nonlinear Lamb wave-mixing was applied in the detection of micro-cracks in plates. The analysis of the nonlinear interaction of these waves with cracks of various lengths and widths was performed using finite-element simulations. The simulation results showed that the sideband at the sum frequency provide a sensitive means for micro-crack detection. Moreover, the sideband amplitudes show a monotonic increase with micro-crack length, but a decrease with micro-crack width. Experiments using Lamb wave-mixing were conducted on plates with fatigue cracks. The experimental results show that a proposed acoustic nonlinearity parameter related to the sideband at the sum frequency is sensitive to micro-cracks in plate, and is well correlated with the damage degree.

A micro-crack initiation simulation model was proposed with varied slip irreversibility and slip hardening (VSISH), by improving the Tanaka-Mura's model. A power law to relate the slip irreversibility parameter to the load and the microstructure information was proposed. The shear strain range in Tanaka-Mura's model was re-derived for introducing slip hardening behavior. Several microstructure examples in three-dimensions were given and the evaluated mean fatigue life has a minimum error less than 3.3% compared with the experimental data. It was demonstrated that the constant-slip-irreversibility strategy and an existing irreversibility model were specific cases of our model.

The shock wave damage during explosive welding has not been reported in a flyer Mo plate of the Mo/Cu clads. However, it would be an inevitable problem in group VI elements. This study was aimed to characterize the shock wave damage in the Mo plate, that is less brittle than a W plate, of explosive welded Mo/Cu clads. Cladding at low horizontal collision velocities leading to high collision angles was expected to enhance the shock wave damage, and the clads resulted in less elongation in bending tests. On the other hand, in the clads obtained at high horizontal collision velocities (HCVs) with low collision angles, their bending elongation increased significantly. The shock wave damage penetrated from the surface of a Mo plate to the Mo/Cu interface, and thus reducing thickness of a Mo plate of bending specimens increased bending plastic strain. The shock wave damage is associated with kinetic energy imparted to the flyer Mo plate, and thus loss of kinetic energy due to formation of an intermediate layer at the interface and reducing thickness of a flyer Mo plate would be very helpful for decrease of shock wave damage.

The pseudo-ductile material behavior of fiber reinforced high performance concrete is mainly characterized by the fiber pullout process. Thereby, complex fiber–concrete interactions, i.e. interface debonding, concrete micro cracks, slippage, adhesion and further unknown processes, are commonly investigated in single-fiber pullout tests. The study in this contribution is based on the experimental results of Gebuhr etal., (2019) and compares three different numerical models applied to the fiber pullout test. An accurate and efficient model for fiber pullout behavior forms the basis for the prediction of the overall behavior by means of composite models or multi-scale approaches in subsequent studies.

The interface of the ternary boride hard cladding material consists of hard phase (Mo2FeB2) and bonding phase (α-Fe). In this paper, on the basis of the ideal interface model of Mo2FeB2 (100)/α-Fe (001) built with the molecular dynamics software, the Mo2FeB2 (100)/α-Fe (001) interface models with micro-cracks parallel with the interface, normal to the interface, and inclined to the interface have been built separately. The interface bonding energies of these four different interface models have been calculated, which shows that the interface model with the micro crack inclined to the interface has the biggest interface bonding energy, while the interface model with the micro crack parallel with the interface has the smallest bonding energy, the interface crack will be the most easily to propagate. The change rule of bonding energy of the interface model with the micro crack parallel with the interface with different lengths has been simulated and analyzed.

Experiments on crack initiation and propagation of double-notched rocks caused by thermal–mechanical loading were carried out by using in-situ SEM observation technique. The results indicated that thermal-induced or thermal–mechanical-induced cracking mechanisms depend strongly on thermal deformation mismatch between the mineral compositions. Micro cracks initiation occurred mainly in the harder and larger quartz grains, but the failure strength of rock did not adequately degrade when surface micro crack density is less than 40 (mm−2). At last, a reliability analysis of 3-parameter Weibull distribution model is presented to discuss the effect of the thermal-induced micro crack on failure strength of rock. Threshold value by thermal-induced micro crack density to influence on the failure strength of crustal rock can be estimated at about 50–60 (mm−2).

The soldered bonding between the Sn-Zn-Cu-Bi system and a Cu substrate was studied and reported herein. The alloying compositions were varied to investigate the effects of Zn, Cu, Bi contents on the solders’ melting temperature (Tm), microstructures, wettability and the intermetallic-compound (IMC) bonding with a Cu substrate. The Sn-7Zn and Sn-9Zn exhibited low Tm (198 °C), but poor wettability on the Cu substrates. Both Cu and Bi additions significantly improved the solder wettability. However, the Tm of the Sn-Zn-Cu series increased sharply to about 225 °C by the addition of 4-wt% Cu. The addition of 3-wt% Bi lowered Tm of the Sn-Zn-Cu alloys by 5 °C. The thickness of the IMC layers between solder and substrate was maximum for Sn-9Zn and significantly decreased with the Cu addition. With the addition of Bi to Sn-Zn-Cu, the IMC thickness increased. The aging of 150 °C for 150 hours minimally affected the IMC-bonding thicknesses of most samples; however, micro crack could be observed along the aged IMC layers.

This paper is focused on a mechanical properties of fine-grained cement based composite materials reinforced by short PVA fibers. Cementitious materials are characterized by their fragile matrix. Reinforcing by fibers (e.g. steel fibers, PVA fibers, PP fibers, glass fibers) increase the tensile strength. The behavior of the elements after developing and spreading of micro cracks under load should be described as a strain-softening, strain-hardening, etc. The multiple cracking under load is typical deformations of composite materials reinforced by short PVA fibers, that is worldwide known as a ECC.

Nonlinear acoustic coefficients have a close relationship with structural cracks. A nonlinear ultrasonic modulation method for micro-crack quantitative evaluation is developed. The influence of phase threshold on the crack evaluation is discussed. Ultrasonic modulation using a unilateral incentive model is applied to the quantitative evaluation of micro-cracks for different specimens. The experimental results indicate that the method can be beneficially applied for micro-cracks detection. A proper phase threshold can improve the reliability of the method based on nonlinear ultrasonic modulation. The presented modulation factor can be used to quantitatively evaluate the structural cracks, and it is suitable for small-crack quantitative evaluation.

Three connecting bolts fractured, which were assembled on the fan used in the internal combustion engine. Detailed fractographic study and metallurgical analysis were focused on the fractured bolts. Fractographic and metallurgical studies indicate that the fracture surface and the microstructure of three bolts exhibit similar features. The fatigue fracture is the main failure mechanism of the bolts. Appearance of the micro-cracks in the thread tip of the fractured bolts makes the stress at the thread regions increase intensively so that the fatigue cracks initiated from the thread regions. Due to the presence of dynamic load, the bolts were never properly tightened during installation which should be responsible for the formation of the cracks.

Substrate materials that are high-temperature stable are essential for sensor devices which are applied at high temperatures. Although langasite is suggested as such a material, severe O and Ga diffusion into an O-affine deposited film was observed during annealing at high temperatures under vacuum conditions, leading to a damage of the metallization as well as a change of the properties of the substrate and finally to a failure of the device. Therefore, annealing of bare LGS (La 3 Ga 5 SiO 14 ) substrates at 800 ∘ C under high vacuum conditions is performed to analyze whether this pretreatment improves the suitability and stability of this material for high temperature applications in vacuum. To reveal the influence of the pretreatment on the subsequently deposited metallization, RuAl thin films are used as they are known to oxidize on LGS at high temperatures. A local study of the pretreated and metallized substrates using transmission electron microscopy reveals strong modification of the substrate surface. Micro cracks are visible. The composition of the substrate is strongly altered at those regions. Severe challenges for the application of LGS substrates under high-temperature vacuum conditions arise from these substrate damages, revealing that the pretreatment does not improve the applicability.

In this experimental research, the effects of cyclic loading at different frequencies on self-compacting concrete were studied. 108 standard cylindrical specimens and 120 cubic specimens were tested. The specimens had compressive strengths of approximately 25 MPa, 35 MPa and 45 MPa. The rate of loading was studied in the 0.05–250 KN/s range. The results showed that the behavior of concrete before and after peak loading depended on the number of loadings as well as the loading rate. Failure of concrete under periodic loading at high frequencies led to increased micro cracks in a direction perpendicular to that of the principal cracks.

Concrete generally deforms and cracks in a non-uniform manner under drying-induced stress. This study used the lattice fracture model to simulate the drying-induced non-uniform deformations, stresses, and micro-crack propagation in concrete. Experiments were designed to validate the lattice fracture model, wherein the drying-induced non-uniform deformations and micro-crack patterns in concrete were measured using a digital image correlation technique and a fluorescent epoxy impregnation method, respectively. It was found that the simulated non-uniform deformations and micro-crack patterns were close to the experimental observations. The interaction mechanism between drying-induced non-uniform stresses and micro-cracks was analysed based on the validated lattice fracture model. The micro-cracks were found to cause stress concentration both in coarse aggregate and the mortar that covered coarse aggregate, which could lead to high micro-cracking risk as drying continues.