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The purpose of this paper is to evaluate theoretically and numerically the stress and stress intensity factor (SIF) at the time of propagation of the crack in bi-material. The problem is formulated using two thin materials which are bound by a cracked adhesive at the tip and having a micro-crack in one of these two materials.

The plane stresses and the SIF will be determined as a function of two parameters (Poisson’s ratio and Shear modulus). The numerical analysis is carried out on a flat element, having a main crack in one of these ends, and a micro-crack varies in the vicinity of this main crack. The problem is analyzed by the finite element method and processed by computational software (ABAQUS).

The numerical and theoretical analysis allowed the author to determine and compare the values of plane stresses and SIF in each area of the material.

The theoretical analysis of SIF is based mainly on a mathematical calculation of equations of plane stresses; these equations are determined by development of complex analytical functions of bi-materials given by other researchers. Using the numerical method, several models are modeled by changing the micro-crack position relative to the main crack to determine the plane stresses and SIF for each position.

An effective machine vision-based method for micro-crack detection of solar cell can economically improve the qualified rate of solar cells. However, how to extract features which have strong generalization and data representation ability at the same time is still an open problem for machine vision-based methods.

A micro-crack detection method based on adaptive deep features and visual saliency is proposed in this paper. The proposed method can adaptively extract deep features from the input image without any supervised training. Furthermore, considering the fact that micro-cracks can obviously attract visual attention when people look at the solar cell’s surface, the visual saliency is also introduced for the micro-crack detection.

Comprehensive evaluations are implemented on two existing data sets, where subjective experimental results show that most of the micro-cracks can be detected, and the objective experimental results show that the method proposed in this study has better performance in detecting precision.

First, an adaptive deep features extraction scheme without any supervised training is proposed for micro-crack detection. Second, the visual saliency is introduced for micro-crack detection.

The interaction between rock mass structural planes and dynamic stress levels is important to determine the stability of rock mass structures in underground geotechnical engineering. In this work, the authors aim to focus on the degradation effects of fracture geometric parameters and unloading stress paths on rock mechanical properties.

A three-dimensional Particle Flow Code (PFC3D) was used for a systematic numerical simulation of the strength failure and cracking behavior of granite specimens containing prefabricated cracks under conventional triaxial compression and triaxial unilateral unloading. The authors demonstrated the unique mechanical response of prefabricated fractured rock under two conditions. The crack initiation, propagation, and coalescence process of pre-fissured specimens were analyzed in detail.

The authors show that the prefabricated cracks and unilateral unloading conditions not only deteriorate the mechanical strength but also have significant differences in failure modes. The degrading effect of cracks on model strength increases linearly with the decrease of the dip angle. Under the condition of true triaxial unilateral unloading, the deterioration effect of peak strength of rock is very significant, and unloading plays a role in promoting the instability failure of rock after peak, making the rock earlier instability failure. Associating with the particle vector diagram and crack coalescence process, the authors find that model failure mode under unilateral loading conditions is obviously distinct from that in triaxial loading. The peak strain in the unloading direction increases sharply, resulting in a new shear slip.

This study is expected to improve the understanding of the strength failure and cracking behavior of fractured rock under unilateral unloading.

Fatigue crack growth rate data for 2024-T3 aluminum are found using three parameters d*, σ* and μ* for short and long cracks for Regions I-III in conventional fatigue. Asymptotic solution of a line crack with a micro-tip is found to yield a singular stress behavior of order 0.75 in contrast to the 0.50 order known for the macrocrack. The difference is due to the micro-macro interaction effects. The three parameters account for the combined effects of load, material and geometry via the tip region. Data for short and long cracks lie on a straight with a slope of about 3.9-4.8 for R values of 0.286-0.565. The results were based on an initial crack a1 mm where a is the half length for a central crack panel. The paper aims to discuss these issues.

The belief that specimen fatigue data could assist the design of structural components was upended when FAA discovered that the NASGRO FCGD are not valid for short cracks that are tight and may even be closed. The regular ΔK vs da/dN model was limited to long cracks. The issue become critical for short cracks connecting the long ones of a few mm to cm or even m according to da/dN for the same crack history. The danger of short/long fatigue crack growth (SLFCG) prompted FAA to introduce an added test known as Limit of Validity (LOV), a way of setting empirical limits for structural components. The dual scale SLFCG data from ΔK micro/macro provide support for the LOV tests.

Data for short and long cracks lie on a straight with a slope of about 3.9-4.8 for R values of 0.286-0.565. The single dual scale relation on ΔK micro/macro can switch from microscopic to macroscopic or vice and versa. The difference is fundamental. Order other than 0.75 can be obtained for simulating different microstructure effects as well as different materials and test conditions.

Scale shifting from short to long fatigue cracks for 2024-T3 aluminum is new. The crack driving force is found to depend on the crack tightness. The sigmoidal curve based on the regular ΔK plot disappeared. The data from ΔK micro/macro for short cracks may supplement the FAA LOV tests for setting more reliable fatigue safe limits.

This paper aims to propose a multi-scale simulation approach for the concrete macro-mechanical damage caused by mixed micro-pore pressures, such as the coupled alkali–silica reaction (ASR) and freeze-thaw cycles (FTC).

The micro-physical events are computationally modeled by considering the coupling effect between ASR gel and condensed water in the mixed pressure and motion. The pressures and transport of pore substances are also linked with the concrete matrix deformation at macro-scale through a poro-mechanical approach, and affect each other, reciprocally. Once the crack happens in the nonlinear analysis, both the micro-events (water and gel motion) and the macro mechanics will be mutually interacted. Finally, different sequences of combined ASR and FTC are simulated.

The multi-chemo mechanistic computation can reproduce complex events in pore structures, and further the macro-damages. The results show that ASR can reduce the FTC expansion for non-air-entrained concrete, but may increase the frost damage for air-entrained concrete. The simulation is examined to bring about the observed phenomena.

This paper numerically clarifies the strong linkage between macro-mechanical deformation and micro-chemo-physical events for concrete composites under coupled ASR and FTC.

Much progress has been made in the past few years in improving the corrosion‐resistance of decorative nickel‐chromium‐plated articles, especially those subjected to outdoor exposure. There now exists a wide range of alternative finishes, all of which are alleged to improve the corrosion‐resistance to some extent. To evaluate these finishes completely, manufacturers are required to spend much time, money and energy. Manufacturers generally wish to improve their standard of corrosion‐resistance of decorative deposits with no increase in cost, and with some of the more complex systems for corrosion protection this is now possible by an overall reduction in nickel thickness.

This study aims to investigate crack propagation in a moisture-preconditioned soft-termination multi-layer ceramic capacitor (MLCC) during thermal reflow process.

Experimental and extended finite element method (X-FEM) numerical analyses were used to analyse the soft-termination MLCC during thermal reflow. A cross-sectional field emission scanning electron microscope image of an actual MLCC’s crack was used to validate the accuracy of the simulation results generated in the study.

At 270°C, micro-voids between the copper-electrode and copper-epoxy layers absorbed 284.2 mm/mg³ of moisture, which generated 6.29 MPa of vapour pressure and caused a crack to propagate. Moisture that rapidly vaporises during reflow can cause stresses that exceed the adhesive/substrate interface’s adhesion strength of 6 MPa. Higher vapour pressure reduces crack development resistance. Thus, the maximum crack propagation between the copper-electrode and copper-epoxy layers at high reflow temperature was 0.077 mm. The numerical model was well-validated, as the maximum crack propagation discrepancy was 2.6%.

This research holds significant implications for the industry by providing valuable insights into the moisture-induced crack propagation mechanisms in soft-termination MLCCs during the reflow process. The findings can be used to optimise the design, manufacturing and assembly processes, ultimately leading to enhanced product quality, improved performance and increased reliability in various electronic applications. Moreover, while the study focused on a specific type of soft-termination MLCC in the reflow process, the methodologies and principles used in this research can be extended to other types of MLCC packages. The fundamental understanding gained from this study can be extrapolated to similar structures, enabling manufacturers to implement effective strategies for crack reduction across a wider range of MLCC applications.

The moisture-induced crack propagation in the soft-termination MLCC during thermal reflow process has not been reported to date. X-FEM numerical analysis on crack propagation have never been researched on the soft-termination MLCC.

The Ni-based superalloy IN-738 LC is known to be susceptible to porosity and different types of cracking during the build-up process and, thus, challenging to manufacture using selective laser melting (SLM). Determining a feasible set of operating parameters for SLM of nickel-based superalloys involves new approach to experimental design based on the Doehlert method that assists in determining an optimal (feasible) set of operating parameters for SLM of IN-738 LC powder alloy.

The SLM parameters are evaluated in terms of their effectiveness in obtaining the microstructure with a porosity content of <0.5 per cent and without micro-cracking. The experimental approach is exemplified with the Doehlert matrix response variable, relative density, by comparing Archimedes method with microstructural assessments of pores and cracks from image analysis. The effect of heat treatment (HT) and hot isostatic pressing (HIP) on the microstructure of the SLMed IN-738 LC powder alloy has been examined and the consequential tensile response characterised.

By using optimised process parameters (low heat input, medium scanning speed and small hatching distance) which provides medium energy density, samples of IN-738 LC with a macroscopic porosity <0.5 per cent and free of micro-cracks can be manufactured by SLM. The results indicate that HIP of SLMed material did not lead to a noticeable effect on mechanical properties compared to HT of SLMed material suggesting that the level of both porosity and crack density might be already below the detection limit for the mere heat-treated material.

SLM processing parameters (power, scan speed, hatching distance) for IN-738 LC were successfully optimised after only 14 experiments using Doehlert design. Two independent methods, Archimedes method and image analysis, were used in this study to assess relative density of SLM-produced samples with sets of processing parameters showing coherency in prediction with predicted response by Doehlert design.

The paper aims to propose a rate‐dependent model of structural concrete in combination with the kinematics of condensed water.

First, the paper proposes the coupling model of water versus cracked concrete with a mathematical completeness of equilibrium and deformational compatibility. The proposed model deals with anisotropy of structural performance and of permeability, which is a particular issue of concrete caused by cracks. The governing equation for saturated concrete in this study is based on Biot's theory that deals with particle assembly as a two‐phase composite. Second, the paper shows the possible reduction of the fatigue life of real‐scale bridge RC decks owing to the water residing in structural cracks under moving wheel‐type loading.

The paper shows that the existence of water possibly has an influence on the rate‐dependency of structural performance. The comparison of transition of pore pressure and principal strain indicates that damage to the concrete skeleton is accelerated by internal stress caused by high pore pressure. It suggests that the existence of water can reduce the fatigue life of bridge decks, especially when the upper layer is saturated.

This paper clarifies the effect of pore water on structural concrete by using numerical model considering kinematics of water.

During steel plate and long-product production, numerous imperfections and defects appear that deteriorate product quality and consequently reduce revenue. The purpose of this paper is to provide a practical overview of typical defects (surface and internal) that occur and their root causes.

The data presented here derive from the quality department and from more than 50 technical reports of ELKEME S.A. on the last decade’s production of steel making companies STOMANA S.A. and SIDENOR S.A., with emphasis on the defects occurred in some of the products of the Bulgarian plant. Stereoscopic observations of surface defects, light optical metallography, and scanning electron microscopy with EDS represent the most used techniques to characterize defected macro-/micro-areas and microstructures.

In general, the most commonly encountered defects from semi-finished (billets, blooms, and slabs) and final (round bar and plate) steel products are as follows: network cracks, porosity, gas holes, shrinkage, shell, slivers, casting powder entrapment, ladle slag entrapment, other non-metallic inclusions, low hot ductility, centerline segregation cracking, macro- and micro-segregation, and mechanical defects (scratches, transverse cracks, and seams).

External and internal quality improvement can reduce the production cost (Euro/ton).

Improvement of the quality of industrial plates and long products increases the safety of the further-produced constructions and systems such as bridges, cranes, heavy equipment, automobile parts, etc.

Root cause analysis and categorization of the most commonly encountered defects can pave the way to production process improvements that directly affect final product quality and the overall per ton production cost. The benefits of this work obviously affect all steel producers/processers, and also society through the safety increase achieved by the quality improvement in the steel products used in constructions and automobile parts.