Increasing Crack Width Research Articles

Study on the Factors Affecting the Self-Healing Performance of Graphene-Modified Asphalt Based on Molecular Dynamics Simulation.

To comprehensively understand the impact of various environmental factors on the self-healing process of graphene-modified asphalt, this study employs molecular dynamics simulation methods to investigate the effects of aging degree (unaged, short-term aged, long-term aged), asphalt type (base asphalt, graphene-modified asphalt), healing temperature (20 °C, 25 °C, 30 °C), and damage degree (5 Å, 10 Å, 15 Å) on the self-healing performance of asphalt. The validity of the established asphalt molecular models was verified based on four physical quantities: density, radial distribution function analysis, glass transition temperature, and cohesive energy density. The simulated healing time for the asphalt crack model was set to 200 ps. The following conclusions were drawn based on the changes in density, mean square displacement, and diffusion coefficient during the simulated healing process under different influencing factors: Dehydrogenation and oxidation of asphalt molecules during the aging process hinder molecular migration within the asphalt crack model, resulting in poorer self-healing performance. As the service life increases, the decline in the healing performance of graphene-modified asphalt is slower than that of base asphalt, indicating that graphene-modified asphalt has stronger anti-aging properties. When the vacuum layer in the asphalt crack model is small, the changes in the diffusion coefficient are less pronounced. As the crack width increases, the influence of various factors on the diffusion coefficient of the asphalt crack model becomes more significant. When the crack width is large, the self-healing effect of asphalt is more dependent on these influencing factors. Damage degree and oxidative aging have a more significant impact on the healing ability of graphene-modified asphalt than healing temperature.

Numerical Simulation Study on Vibration Characteristics and Influencing Factors of Coal Containing Geological Structure

Accurately determining the natural frequency of coal-containing geological structures is crucial for preventing mine dynamic disasters and utilizing vibration waves to break coal and enhance its permeability. Based on the modal theory of rock, vibration models of coal-containing geological structures, including layering and fractures are established. By analysis, the undamped vibration equation and its characteristic equation for both the layered coal system and the fractured coal system are derived. Subsequently, the Lanczos method is employed to solve the system’s vibration modes using ABAQUS. The effects of the layering position, layering thickness, layering physical properties, crack width, and crack length on the natural frequency and vibration response of coal-containing geological structures are investigated. The results indicate that when a single influencing factor is altered, the displacement response distribution of the coal body vibration system with geological structures remains essentially the same, and these single influencing factors have a minimal impact on the vibration displacement of the coal-containing geological structure. The natural frequency of the system decreases exponentially as the distance between the layering and the geometric center of the coal system with geological structures increases. The presence of layering in the coal system with geological structures significantly reduces the system’s natural frequency. The natural frequency of the coal system with geological structures increases in a power function manner as the layering elastic modulus increases. Conversely, the natural frequency decreases with an increase in crack length. When the change ranges of crack width and bedding thickness are the same, the natural frequency of the fractured coal body system exhibits more significant changes. The natural frequency of the coal system with geological structures initially decreases and then increases as bedding thickness and crack width increase. The trend in the natural frequency changes and the position of the extreme point are related to the ratio of the elastic modulus and density of the geological structure.

The development of multiplexing capability for reflective matched fiber bragg gratings interrogation technique and its application in real-time micro cracks detection

Abstract Cracks detection in engineering structures is pivotal for ensuring structural reliability and preventing catastrophic failures. In this article we developed multiplexing capability of reflective matched fiber Bragg Gratings (RM-FBGs) interrogation technique and utilized it for crack detection in an assembly aluminum plates. Firstly, the proposed multiplexing capability is analyzed by applying axial strain on an array of five FBGs pasted on five separate aluminum assemblies. The strain in any FBG due to localized micro-crack resulted in variation its output itself by ascertaining no effect in the outputs of other FBGs, certifying the multiplexing capability of RM-FBGs scheme. The developed RM-FBGs scheme is practically applied micro-cracks detection in a V-shape crack produced in assembly of aluminum plates. The crack is monitored by an array of three multiplexed FBGs epoxied to the plate’s junction at three different positions P1, P2 and P3. Where P1 is at beginning, P2 is at middle and P3 is at end of the crack. Sensitivities of the FBGs at points P1, P2 and P3 were found to be 0.09 ± 0.0001 V μm−1, 0.10 ± 0.007 V μm−1 and 1.08 ± 0.09 V μm−1, respectively and resolutions were found to be 0.22 μm, 0.20 μm and 0.02 μm, respectively. Variation in gauge length of the optical fiber from 100 mm to 200 mm resulted in 76.36% increase in crack width sensing range but at the cost of compromise in sensitivity and resolution. The proposed multiplexed RM-FBG can be deployed for early micro-cracks detection in metallic and non-metallic structures with sub-micrometers resolution.

Study on calcium dissolution of concrete specimens with surface cracks

The effects of crack width, crack depth and water-cement ratio (w/c) on calcium dissolution resistance of cracked concrete were evaluated. Results show that the degradation in physical properties and mechanical properties of concrete after dissolution increase with the increasing crack width, crack depth and w/c. In the case of concrete with w/c of 0.40 and dissolution age of 100 d, the degradation of splitting tensile strength of specimens with crack widths of 0.1, 0.2 and 0.3 mm was 1.27 times, 1.39 times and 1.54 times that of uncracked specimens. Dissolution resistance of cracked concrete is obviously lower than that of uncracked concrete, and the effect of crack width on it is more significant than that of crack depth, and the higher the w/c of concrete, the more significant the effect of crack width. Dissolution damage increasing coefficient of cracked concrete can be used to quantitatively characterise the effect of cracks on the dissolution damage of concrete, and its maximum value is approximately 1.08 corresponding to the crack width of 0.3 mm. The results of this study can be used as a reference for the accurate evaluation of calcium dissolution resistance and service life of the water-related concrete structures.

Self-healing efficiency of later-age cracked microbial mortar embedded with unencapsulated microorganisms under long-term water and ambient exposure conditions

To ensure the long-term self-healing ability of concrete structures throughout their lifespan is a crucial requirement for Microbially Induced Carbonate Precipitation (MICP) technology. In this study, unencapsulated microbial cells were directly mixed into the fresh mortar as a component to investigate their efficiency in repairing later-age cracks, respectively exposed to long-term water environment and ambient conditions. The crack width repair ratio for samples with cracks initially created by splitting tests was calculated at healing intervals of 6 and 12 days, revealing a sixfold higher repair ratio in 150-day samples with initial widths below 200 μm than those cases with 500 μm-wide cracks. The 26.3 % reduction in water absorption content after a 12-day healing period reflected an effective healing result for cracks and capillary pores. The microbially induced calcite precipitations were confirmed through SEM, XRD, and EDS analysis, with complete crack closure observed for 150-day samples with widths less than 200 μm. However, it was also found that the self-healing efficiency decreased with increasing crack width due to the limited availability of healing agents, with the maximum completely healed crack width of 507.8 μm. Despite prolonged exposure, no further reduction in crack width and sorptivity was observed, highlighting the challenges in achieving a complete healing effect. Surface images obtained from microscopes revealed the enduring presence of unencapsulated microorganisms, corroborating their role in continuous calcite precipitation and crack filling.

Hybrid Fiber Influence on the Crack Permeability of Cracked Concrete Exposed to Freeze-Thaw Cycles.

This paper describes hybrid fiber's influence on the crack permeability of cracked concrete exposed to freeze-thaw cycles. A permeability setup and a laser-scanning setup have been designed to measure the crack permeability and the fractured surface roughness of cracked hybrid fiber-reinforced concrete, containing polypropylene fiber and steel fiber, under a splitting tensile load. The results show that, when the effective crack width of the specimens is less than 25 μm, the rough crack surface significantly reduces the concrete's crack permeability. As the crack width increases, the effect of the concrete crack surface on crack permeability gradually decreases, and the crack permeability of the concrete is closer to the Poiseuille flow model. The permeability parameter α derived from the Poiseuille flow model is effective for assessing the crack permeability of concrete. Compared to the modified factor ξ of crack permeability, the permeability parameter α can effectively evaluate and quantify the development trend of crack permeability within a certain range of crack widths. The permeability parameter α of SF20PP2.3, subjected to the same freeze-thaw cycles, decreases by 16.3-94.8% compared to PP4.6 and SF40, and SF20PP2.3 demonstrates a positive synergistic effect on the crack impermeability of cracked concrete. The crack impermeability of SF40PP2.3, subjected to the same freeze-thaw cycles, lies between that of PP6.9 and SF60. The roughness of crack surface (X) and the crack permeability (Y) are highly correlated and follow an exponential curve (Y = 1.0415 × 107·e-6.025·X) in concrete. This demonstrates that hybrid fibers enhance crack impermeability by increasing the crack surface roughness. Furthermore, the combination of polypropylene fiber and steel fiber effectively promotes the formation of micro-cracks and facilitates the propagation of multiple cracks in the concrete matrix. This combination increases the head loss of water flow through the concrete and decreases the crack permeability.

Research on Magnetic Field-Based Damage Detection Technology for Ferromagnetic Microwires

Composite materials are frequently exposed to external factors during their operational service, resulting in internal structural damage which subsequently impacts their structural performance. This paper employs ferromagnetic materials for their sensitivity to magnetic field strength. By detecting variations in the magnetic field within the embedded ferromagnetic microwires of composite materials, the aim is to indirectly assess the health status of the composite materials. Firstly, a theoretical numerical model for magnetic field intensity at the crack site was established. Subsequently, a finite element model was employed to analyze the variations in the magnetic characteristics of ferromagnetic microwires at the crack site. Under different parameter conditions, the patterns of magnetic signals at the crack site were determined. The results indicate that with an increase in the angle between the external magnetic field and the crack, the fitted curve of the magnetic signal shows a linear increase. The distance between the peak and valley of the radial magnetic signal in the axial direction decreases, and the axial magnetic signal transitions from double-peak to single-peak. With the increase in crack depth, the fitted curve of the magnetic signal shows a linear increase, and the magnetic signal at the crack tip also exhibits a linear increase. An increase in crack width leads to a non-linear decrease in the fitted curve of the magnetic signal, and after reaching a certain width, the magnetic signal stabilizes. For two identical cracks at different distances, the magnetic signal exhibits a transition from a complete pattern to two complete patterns. With the increase in the external magnetic field, the magnetic signal shows a completely regular linear increase. By analyzing and calculating the variations in magnetic signals, the patterns of magnetic characteristics under the damaged state of ferromagnetic microwires were obtained. This serves as a basis for assessing whether they can continue in service and for evaluating the overall health status of composite materials.

Study on Crack Resistance and Calculation Model of RAC Beams Strengthened with Prestressed CFRP

With the development of recycled aggregate concrete (RAC), the recovery rate of construction waste is improved, and the pollution problem is alleviated. In particular, RAC beams strengthened with prestressed carbon fiber reinforced plastics (CFRP) can exhibit improved mechanical properties, expanding RAC application. Four groups of reinforced RAC beam specimens contained 0%, 40%, 70%, and 100% recycled coarse aggregate, respectively. Each group of beams was first pre-cracked and then strengthened by prestressed CFRP with one layer and two layers respectively. Finally, the bearing capacity tests were performed for these beams. The test results show that as the recycled coarse aggregate content increases, the cracking moment and ultimate load capacity of the beam decrease, while its crack width increases. As the CFRP layer increases, the deformation and crack width of the beam decreases, while the number of cracks increases. The prestressed CFRP also exhibited tensile and peeling failure. A beam deflection calculation model was established by introducing a coefficient k representing the interaction between recycled aggregate and CFRP. The influence coefficient of concrete elongation on the crack width and average crack spacing of the beam was modified, and the crack width analysis model of the beam was established. The calculated results are in good agreement with the experimental observations. It can provide reference for the application and design of recycled concrete beams strengthened with prestressed CFRP.

Effect of load on bonding properties and salt freeze-thaw resistance of bridge expansion joint concrete

In the seasonal frozen regions, the bridge expansion joint concrete (BEJC) is susceptible to damage during its service life, not only from vehicular loads but also from chloride salt erosion and the effects of freeze-thaw cycles. This study investigates the basic physical and mechanical properties of BEJC under different curing conditions. A rapid chloride permeability test was conducted to comparatively analyze the concrete's chloride ion penetration resistance. The microscopic crack width on the concrete bond surface is evaluated to assess the concrete bond performance under different loading durations. Additionally, the study explores the coupled effect of wheel loads and single-sided salt freeze-thaw cycles (WL-SFT) on the freeze-thaw resistance of BEJC, delving into factors such as spalling mass, water absorption rate, and pore structure characteristics (including air content, specific surface area, spacing coefficient) and connectivity. The results indicate that for specimens subjected to loading at 1–14 days and 3–14 days, the average crack widths on the bond surface are 14.36 µm and 10.09 µm, respectively, representing 5.27 times and 3.70 times those of unloaded specimens. The bond strength also decreases by 34.8% and 14.2%, respectively, compared to unloaded specimens. The increase in crack width leads to a reduction in bond strength, highlighting the importance of bond strength as a consideration for the actual opening time of roads in engineering projects. Furthermore, due to its smaller and more stable pore structure, the study suggests that WL-SFT almost does not damage standard curing (SC) concrete; however, it slightly disrupts the pore structure of natural curing (NC) concrete. In comparison, WL-SFT leads to the generation of more microcracks in both the surface and deeper layers of low-temperature curing (LC) concrete, resulting in the destruction of its pore structure and connectivity.

Laser-Powder Bed Fusion Additive Manufacturing of NiCrBSi Self-Fluxing Nickel Alloy, Material Health - Process Relationship

Laser Powder Bed Fusion (L-PBF) might be a promising solution for producing complex wear-resistant parts from NiCrBSi self-fluxing nickel alloys. This study investigates a large set of parameters with a baseplate heated up to 500 °C. Furthermore, laser remelting is also explored to further increase surface density and reduce cracking. Material health is deeply investigated by image analysis to quantify different defects (lack of fusion, porosity and cracks). Spatters likely induce lacks of fusion, while the low toughness and high hardness values cause cracks. The lack of fusion surface fraction and crack length decrease with the preheating temperature while the crack width increases. A surface density of 99 % is obtained with careful process optimisation leading to a laser power of 100 W, a laser speed of 750 mm.s-1 and a preheating temperature of 500 °C.

Experimental study on crushing of concrete slabs by high-voltage pulse discharge

To investigate the effectiveness of high voltage pulse discharge (HVPD) in crushing concrete slabs, HVPD in-liquid tests were conducted in pre-drilled holes in three double-layer bi-directionally reinforced and twelve single-layer bi-directionally reinforced concrete slabs. The parameters that were varied in the tests included the concrete strength, discharge hole diameter and spacing, discharge voltage and number of copper wires discharged. The results showed that the explosion caused by HVPD using copper wires increased the crack width by more than 34.8% compared to that caused by the electrohydraulic effect. After 10 explosions caused by HVPD using copper wires, the single-layer reinforced concrete slab was split into several slabs by cracks to achieve the crushing effect. The single discharge energy, i.e., discharge voltage, had a significant effect on the crushing of concrete slabs, and the width of concrete cracks produced by a 100 kV discharge was more than twice that of a 40 kV discharge. The increase in concrete strength acted as a crack arrestor for the slabs, and the crack width of C20 concrete slabs increased by approximately 10% to 25% compared to C40 concrete slabs. The increase in crack width with increasing number of discharged copper wires decreased with increasing discharge voltage. The width of concrete cracks produced by the explosion of 60 copper wires compared to 30 copper wires increased by approximately 10% at 100 kV and by approximately 20% from 60 to 80 kV. The crack width of concrete slabs with discharge holes of diameter 40 mm increased by approximately 5% to 15% compared to concrete slabs with holes of 50 mm. Expressions for the relationships between the damage degree of the concrete slab (i.e., the width of the concrete cracks around the holes on the outside of the slab) and the key parameters such as the output voltage, the number of discharged copper wires, and the strength grade of the concrete were established based on the experimental results.

Permeability coupling model of multiple migration mechanisms in rough micro-fractures of shales

To study the gas transmission characteristics in organic pores of rough shale reservoirs, firstly, considering the effect of roughness, adsorption layer, and stress sensitivity on fracture width variation, the effective fracture width model was established. On this basis, the real gas transport models of the adsorbed gas and bulk gas in rough reservoirs have been studied respectively, and the apparent permeability coupling model of rough microfracture of shale are proposed according to the difference of actual flow area. The validity of the proposed models was verified by comparing them with the simulation data, and the contribution of each migration mechanism to the total flow under different roughness and fracture width variation factors was analyzed. It is found that the formation pressure is proportional to the influence of roughness on permeability. When the initial crack width increases, the corresponding pore pressure decreases when the roughness has a greater influence on the proportion of slip flow. The influence of roughness on the Knudsen diffusion ratio and surface diffusion ratio will be greater when the initial crack width is smaller. In addition, if the initial crack width and pore pressure are constant, the greater the relative roughness, the greater the Knudsen diffusion ratio and surface diffusion ratio, and the smaller the slippage flow proportion.

Experimental and theoretical analysis of cracking and tension stiffening in UHPFRC under high‐cycle fatigue

AbstractTension‐stiffening controls the serviceability behavior of concrete structures as it is responsible for crack formation and, consequently, the deflection of beams. In fiber reinforced concrete, such as ultra‐high performance fiber reinforced concrete (UHPFRC), fibers bridge cracks and thereby transfer tensile stresses across the cracked region, allowing for tensile stresses to be carried by the concrete within the cracked region. Due to structures being designed for longer design lives, the consideration of long‐term effects such as fatigue is required. Much research has examined tension‐stiffening under fatigue when subjected to low cyclic loading, but very little has considered the effects of high‐cycle fatigue, especially for UHPFRC. This paper presents the results of nine UHPFRC tension‐stiffening tests under high‐cycle fatigue in which the crack formation and development under varying cyclic ranges were studied. Specimens were subjected to as many as 5.7 million cycles, and crack readings were taken during each test. The experimental results demonstrate the random nature of cracking on UHPFRC as well as the increase in the crack width under cyclic loads. Finally, this research described the extension of an existing partial‐interaction mechanics model to allow for the stress in the fibers and the increase in crack width due to high cycle fatigue.

Mesoscopic modeling and simulation of tensile properties of cracked concrete using cohesive model

A random aggregate (RA) model consisting of mortar, aggregate, and the interfacial transition zone (ITZ) was established to investigate the effect of existing cracks on the tensile properties of concrete. Based on this, a method for establishing a geometric model of cracked concrete was proposed by inserting 0-depth cohesive elements into the RA model. The influence of crack length, width, and area on the tensile properties of concrete were studied using the established cracked concrete model. In addition, the key parameters of bond strength and fracture energy of the mortar and ITZ regions were tested. The cement is ordinary Portland cement with a strength grade of 42.5, and the sand is medium sand. The fracture energy tests were conducted using a displacement-controlled loading model with a loading rate of 0.4 mm/min, while the tensile strength tests were conducted using a stress-controlled loading method with a loading rate of 0.06 MPa/s. The feasibility and accuracy of the numerical method used were verified by comparing the results with those of a finite compression simulation. The numerical results show that as the crack length increases, the tensile strength and elastic modulus of concrete gradually decrease, but if the crack length is 0.47 h, the elastic modulus of concrete shows an abnormal increase. The range of the crack's influence on the tensile performance of concrete is between 50 mm and 100 mm. If the crack width is less than 0.55 mm, the tensile strength of concrete gradually decreases with the increase of crack width, and when the crack width is greater than 0.55 mm, the tensile strength stabilizes.

Experimental Study on the Influence of Transverse Crack on Chloride Ingress in Concrete Slab Track of High-Speed Railway.

The concrete track slab and the base slab of the high-speed railway CRTS II track structure are prone to transverse cracks in the initial service period, which are subjected to environmental action and train load. In order to investigate the influence of transverse cracks on chloride ingress of concrete track slab and base slab in a coastal environment, drying-wetting cycle chloride erosion tests were carried out on reinforced concrete track slab and base slab specimens with cracks ranging from 0 mm to 0.6 mm, subjected to continuous bending moment. The chloride ion concentration of concrete along the depth direction was collected during the test process. The experimental results show that the chloride ion concentration of concrete at the crack section is much higher than that at the intact section, and it increases with the increase of crack width in the range of 0.2 mm to 0.6 mm. A chloride diffusion coefficient model of cracked concrete is proposed for slab track based on the experimental results, which can comprehensively consider the effects of surface chloride ion concentration, chloride binding effect, time-varying effect, temperature, relative humidity, and transverse crack width.

EIS based assessment of electrodeposition effect of concrete cracks: Experiment and equivalent model

In this study, the electrochemical impedance spectrum (EIS) is proposed to evaluate the effectiveness of concrete cracks repaired through electrodeposition. The EIS responses of the concrete cracking and electrodeposition repairing processes are investigated. The obtained results show that the impedance of concrete decreases with increasing crack width. The impedance of concrete increases gradually during the electrodeposition process. In order to characterize and forecast the EIS responses during the concrete cracking and electrodeposition repairing processes, a new equivalent circuit model is proposed. The crack repairing rates are defined in terms of the crack resistance and total impedance of concrete. After 14 days of electrodeposition repairing, the crack repairing rates can eventually reach 79.35% and 77.81% in terms of crack resistance and total impedance, respectively. In addition, the influences of the w/c ratio, crack width, and crack tortuosity of concrete on the EIS responses of concrete repaired by the electrodeposition process are calculated and discussed.

Self-Healing of Aged Concrete Containing Crystalline Admixture and Expansive Agent under Repeated Loading

While self-healing concrete has been increasingly studied this past decade, research on the self-healing of a crack after repeated loading is still scarce. Studying this topic is of utmost importance because structures in practice are subjected to repeated damage, causing a variety of crack openings. Hence, this paper presents an evaluation of the self-healing properties of aged concrete containing a combination of crystalline admixture (CA) and expansive agent (CSA), and submitted to repeated loading. Pre-cracked at 218 days old by means of a three-point bending test, the prisms were reloaded every three weeks and healed in wet/dry cycles in between. After two loadings, they were reloaded a third time until failure. Two types of reloading procedures were carried out: (1) reloading to the same residual crack width; and (2) reloading with increasing crack width. Self-healing was assessed with water permeability measures before and after each reloading, macroscopic observations of the cracks, and mechanical recovery. The results showed that two phenomena occurred with opposite effects: damage versus healing. The magnitude of both processes depends on the reloading procedure. When reloading to the same crack width, the damage effect was lower than the healing effect, indicating that the healing products provided sealing even after repeated loading. When reloading with an increasing crack width, the damage effect was greater than the healing effect, but the healing rates were higher than reloading to a constant crack width, because of the creation of new fresh crack surfaces that healed faster. In any case, multiple damage slows down healing but the self-healing process continues. This confirms the long-term healing potential of cracked structures made of, or repaired with, self-healing concrete.

Influence of cracks on loess collapse under heavy rainfall

Collapse is one of the frequent geological disasters on the Loess Plateau, which seriously threatens the safety of people's life and property. Taking the typical loess collapse in Wangdonggou, Changwu County, China as the research object, the loess collapse model is established through the field geological investigation and laboratory tests. Based on the principle of fluid–solid coupling, the failure mechanism of collapse body with the different crack depth and crack width are numerically simulated by the finite element method to study the influence of cracks on loess collapse under the action of heavy rainfall. The results show that with the infiltration of rainfall, on the one hand, the self-weight of the collapse body increases, which causes the increase of shear stress at the slope foot. On the other hand, when rainwater seeps out from the slope surface, it generates the seepage force, resulting the increase of the overturning moment of the collapse body. When the crack depth gradually increases from 0 to 6.0 m, the tensile stress at the crack tip gradually increases, the trend of collapse body toppling towards the free face is more and more obvious, the plastic zone gradually expands from the slope foot to the crack tip, and the safety factor of the collapse body decreases from 1.135 to 0.958. With the increase of crack width, the gravity center of collapse body gradually moves outward, the soil deformation at the slope foot and crack tip gradually increases, and the stability of the collapse body continuously decreases. The failure process of toppling loess collapse includes tensile crack initiation, crack expansion and collapse body bending and toppling. The results reveal the influence of crack depth and crack width on the stability of the collapse body under the action of rainfall, as well as the instability failure mechanism of the collapse body, which can provide theoretical support for the prevention and control of collapse geological disasters and soil gravity erosion in Loess Plateau.

Effects of interface cracks on reliability of surface mount technology interconnection in service environment

PurposeSurface mount technology (SMT) is widely used and plays an important role in electronic equipment. The purpose of this paper is to reveal the effects of interface cracks on the fatigue life of SMT solder joint under service load and to provide some valuable reference information for improving service reliability of SMT packages.Design/methodology/approachA 3D geometric model of SMT package is established. The mechanical properties of SMT solder joint under thermal cycling load and random vibration load were solved by 3D finite element analysis. The fatigue life of SMT solder joint under different loads can be calculated by using the modified Coffin–Manson model and high-cycle fatigue model.FindingsThe results revealed that cracks at different locations and propagation directions have different effect on the fatigue life of the SMT solder joint. From the location of the cracks, Crack 1 has the most significant impact on the thermal fatigue life of the solder joint. Under the same thermal cycling conditions, its life has decreased by 46.98%, followed by Crack 2, Crack 4 and Crack 3. On the other hand, under the same random vibration load, Crack 4 has the most significant impact on the solder joint fatigue life, reducing its life by 81.39%, followed by Crack 1, Crack 3 and Crack 2. From the crack propagation direction, with the increase of crack depth, the thermal fatigue life of the SMT solder joint decreases sharply at first and then continues to decline almost linearly. The random vibration fatigue life of the solder joint decreases continuously with the increase of crack depth. From the crack depth of 0.01 mm to 0.05 mm, the random vibration fatigue life decreases by 86.75%. When the crack width increases, the thermal and random vibration fatigue life of the solder joint decreases almost linearly.Originality/valueThis paper investigates the effects of interface cracks on the fatigue life and provides useful information on the reliability of SMT packages.

Strength Recovery Effect of Bisphenol A Epoxy Resin E44 on Rock Masses with Various Crack Widths

As a desirable bonding and repair material, epoxy resin combined with other materials is widely used in civil engineering, but its application in underground rock engineering is still limited compared with the wide use of cement grout. To explore and optimize the effect of room temperature-cured bisphenol A epoxy resin E44 on the strength recovery of rock samples with cracks of various widths, the uniaxial compressive strength (UCS) of epoxy resin was studied and the mass ratio of the curing agent to epoxy resin ( k C E ) was adjusted and optimized. On this basis, the UCS of the selected epoxy resin was investigated by adding diverse amounts of ethanol so that the ratio corresponding to the repair material with better mechanical properties could be selected. Artificial cracks of various widths were filled with the optimized materials, and then, a UCS test was conducted on the repaired rock samples to evaluate the effect on strength recovery and compare it with that of ultrafine Portland cement (UPC). The results show that the UCS of epoxy resin stones increases when k C E ≤ 0.25 and decreases when k C E > 0.25, reaching a peak of 92.41 MPa. Furthermore, as the mass ratio of ethanol to curing agent and epoxy resin ( k A ) increases, the UCS increases to 94.65 MPa for k C E = 0.25 and k A = 0.01. The crack width influences the UCS of the repaired rock mass. With increasing crack width, the effect of epoxy resin on recovery continuously improves, whereas that of UPC shows the opposite trend. Compared with UPC, epoxy resin has an overwhelmingly greater effect on strength recovery. For instance, for a 3 mm-wide crack, the recovered UCS for 28 d epoxy resin is 83.48 MPa, with much larger peak strains, and the strength recovery rate ( k r ) is 77.55%; however, the k r of UPC is only 15.12%.