Main Failure Form Research Articles

Effect of Substrate Pretreatment Process on the Cutting Performance of Diamond-Coated PCB Micro-Milling Tools

Diamond coatings were deposited on PCB (printed circuit board) carbide milling tool substrates under various schemes of acid and alkali pretreatment by hot filament chemical vapor deposition (HFCVD). Scanning electron microscopy and X-ray coating analysis were used to examine the surface morphology of the milling tools and the impact of de-cobalt from the substrate surface after pretreatment. Milling experiments were carried out to study the cutting performance of diamond-coated PCB micro-milling tools under various pretreatment processes. The results show that abrasive wear, coating flaking, and cutting-edge chipping are the main failure forms of coated PCB milling tools. The substrate pretreatment process with 20 min of alkali etching followed by 20 s of acid etching allows the diamond-coated micro-milling tools to produce the best film-substrate adhesion and substrate strength. These milling tools also have the longest service lives and are suitable for the high-speed cutting processing of PCB.

Simulation analysis on seismic dynamic response of pile supported tunnels in deep backfill area of soil-rock mixture

To reveal the seismic dynamic response of the pile-supported tunnel group in the soil-rock mixture deep backfill region, a three-dimensional finite element model was established based on the engineering conditions of the subway section and three tunnels with close access lines. Subsequently, the seismic dynamic response of the tunnel lining structure was studied. The results show that: Under the action of seismic, the soil-rock mixture stratum presents nonlinear characteristics with shear failure and plastic deformation. In addition, the acceleration and earth pressure of the soil-rock mixture stratum is in a “saturated” state; The seismic dynamic response of the three tunnels influences each other. The bending moments in the X and Y directions of the tunnel lining cross-section are distributed in “X” and inverted “V” shapes, respectively. Meanwhile, the tensile stress and shear stress are distributed in an “X” shape; Under the action of seismic, the main failure form of tunnel lining is tension shear failure, and the most vulnerable position is the left and right arch foot, followed by the left and right arch shoulder; The bending moment of the pile body changes nonlinearly in the height direction. The most significant bending moment value appears at the top 1/5 of the pile length and the junction of different strata. Furthermore, the most significant horizontal displacement of the lining structure occurs at the tunnel vault.

Ring Stiffened Cylindrical Shell Structures: State-of-the-Art Review

The cylindrical shell is a widely used structure in engineering practice, and its main form of failure is instability due to buckling. As a classical problem in the field of mechanics, the stability of cylindrical shells has been studied extensively. However, the large difference between the theoretically predicted results of the critical buckling load and the experimental results for the cylindrical shells subjected to uniform axial pressure has contributed to the continuous development of the shell stability theory. This paper briefly reviews the development of the shell stability theory, then presents an overview of the current status and trends of stability research on the stiffened cylindrical shell widely used in cylindrical shell structures in real engineering, and finally presents the difficulties and directions of future stability research on cylindrical shell structures in engineering applications.

Physical and mechanical properties of coral aggregates in the South China Sea

Coral aggregate (CA) is a type of marine resource with rich storage capacity and complex physical characteristics, and it is increasingly recognized as an important island engineering material. For the regional variability of CA in the South China Sea, the physical and mechanical properties of different CAs were experimentally studied in this paper. Using the X-ray Computed Tomography technique, the pore characteristics of CA were quantitatively studied in term of the pore shape, size, sphericity, number, volume, etc. Additionally, the uniaxial compressive properties of cylinder CA samples were investigated in term of the failure patterns, stress-strain curves, elastic modulus, strength, and toughness. Results indicate that different CA samples contain a considerable amount of pores with different shapes that are closely related to the coral growth environment. It was found that content of the millimeter-sized pores with a diameter of 0.5∼1 mm is the highest, while the content of the centimeter-sized pores with a diameter greater than 1 cm is the lowest. The porosity of light and heavy CA was determined as 1.37%–22.55% and 3.72%–22.64%, respectively. Splitting failure is the main form of failure to CA under uniaxial compression loading. While the compressive toughness of CA could be effectively improved by the surface-filling method treatment using coral mortar. According to the present results and the existing data, a series of regression equations concerning the physical-mechanical properties of CA were established, which has significant values for the study and application of CA in the South China Sea.

CFD-Based Physical Failure Modeling of Direct-Drive Electro-Hydraulic Servo Valve Spool and Sleeve.

Direct-drive electro-hydraulic servo valves are used extensively in aerospace, military and control applications, but little research has been conducted on their service life and physical failure wear. Based on computational fluid dynamics, the main failure forms of direct-drive electro-hydraulic servo valves are explored using their continuous phase flow and discrete phase motion characteristics, and then combined with the theory of erosion for calculation. A mathematical model of the direct-drive electro-hydraulic servo valve is established by using Solidworks software, and then imported into Fluent simulation software to establish its physical failure model and carry out simulation. Finally, the physical failure form of the direct drive electro-hydraulic servo valve is verified by the simulation results, and the performance degradation law is summarized. The results show that temperature, differential pressure, solid particle diameter and concentration, and opening degree all have an impact on the erosion and wear of direct-drive electro-hydraulic servo valves, in which differential pressure and solid particle diameter have a relatively large impact, and the servo valve must avoid working in the range of high differential pressure and solid particle diameter of 20–40 um as far as possible. This also provides further theoretical support and experimental guidance for the industrial application and life prediction of electro-hydraulic servo valves.

Preparation and Mechanical Properties of High Silicon Molybdenum Cast Iron Materials: Based on Deep Learning Model.

In the production and life of machines, wear is the main form of material failure. Many workpieces and equipment will produce friction and wear during use, causing energy and material consumption, resulting in huge economic losses. In the process of using engineering equipment, in order to improve the service life of the workpiece and improve the wear-resistant material, the research of the material itself must be closely linked with the wear mechanism. Among the antiwear materials, the application of high-chromium cast iron is the most common. The reason is that high-chromium cast iron has a series of advantages in performance, manufacturing technology, and price. However, high-chromium cast iron itself has high C content and high brittleness, resulting in defects in toughness and poor corrosion resistance. When working in harsh environments such as mechanical extrusion, high-strength wear, and chemical corrosion, cracking and deformation are prone to occur, corrosion and peeling, and another damage failure. High chromium cast iron must have a relatively stable structure, good strength and toughness, excellent wear resistance, and corrosion resistance. In this study, the static corrosion performance of high-chromium cast iron was tested to study the effects of Mo and V elements addition and content changes on corrosion resistance and vanadium, molybdenum, and subcritical treatment processes on the microstructure and properties of high-chromium cast iron, in order to obtain better performance. Lower cost high chromium cast iron castings. As a wear-resistant part, high-chromium cast iron castings are widely used in wear and can cope with harsh working environments, but their excellent hardness conditions bring certain defects in toughness and at the same time lack good corrosion resistance, in mechanical extrusion., high-strength wear, chemical corrosion, and other harsh environments are prone to damage and failure. Therefore, high-chromium cast iron should have dual properties, not only high hardness but also suitable for mud, sand, chemicals, and other media corrosion and wear resistance.

Effects of coarse aggregates on the mechanical properties, durability and microscopic behaviour of mortar rubble

A new type of slope protection structure, mortar rubble arch slope protection, has good low-temperature performance, and it is mostly used in the seasonally frozen area of North China. To determine the effects of aggregate type (basalt, granite, limestone) and amount of coarse aggregate on mortar rubble, mechanical properties were measured and durability experiments were conducted. Compressive strength, bending strength, mechanical damage characteristics of the materials, freeze–thaw loss rates and temperature shrinkage coefficients were recorded. The results were verified by microscopic observations. Using the digital image correlation (DIC) test system, the main form of the bending failure of the mortar rubble was observed to be failure around the aggregate. Acoustic emission parameters were used to accurately reflect the damage characteristics of the mortar rubble during the compression test. The resistance time of basalt before failure was long, and its peak energy was high. The durability test results showed that granite mortar rubble had better frost resistance, a higher freeze–thaw resistance factor, and less temperature shrinkage deformation than the basalt and limestone rubbles, and it is more suitable for slope protection in cold areas. Scanning electron microscopy (SEM) results showed that the matrix entered the pores to form new bonds, which was the main reason for the high strength of the basalt specimens. The basalt mortar rubble interface was severely damaged after freezing and thawing. The optimal amount of added aggregate was approximately 60%-70%, which resulted in good mechanical properties and durability of the mortar rubble. When the flake aggregate content exceeded 70%, the strength and durability of the material decreased.

Prediction of Creep Curves Based on Back Propagation Neural Networks for Superalloys.

Creep deformation is one of the main failure forms for superalloys during service and predicting their creep life and curves is important to evaluate their safety. In this paper, we proposed a back propagation neural networks (BPNN) model to predict the creep curves of MarM247LC superalloy under different conditions. It was found that the prediction errors for the creep curves were within ±20% after using six creep curves for training. Compared with the θ projection model, the maximum error was reduced by 30%. In addition, it is validated that this method is applicable to the prediction of creep curves for other superalloys such as DZ125 and CMSX-4, indicating that the model has a wide range of applicability.

Coal Wall Instability Evolution Law of Large Mining Height Face in Steeply Dipping Hard Roof Soft Coal Seam

The coal wall of large mining height longwall fully mechanized face in steeply dipping coal seam has poor self-stability and high probability of instability, which is likely to induce secondary hazards such as support instability and flying gangue once catastrophic occurs, increasing the difficulty of surrounding rock control and production risk. Coal wall disaster prevention and control can improve the productivity of this type of face, and this is based on the sufficient understanding of damage patterns such as internal and external dispersion of coal wall pressure, deformation, and displacement; in order to clarify the coal wall dynamic failure law of large mining height face in steeply dipping coal seam, numerical calculation, field measurement, theoretical analysis, and other methods are comprehensively applied to the study. The results show that the coal wall bearing of large mining height face in steeply dipping coal seam is distributed asymmetrically, the stress concentration position in the upper and middle part of the face is closer to the coal wall than the lower part, the stress concentration degree is also larger than the lower part, and the stress concentration coefficients from upper to lower are 1.37, 1.50, and 1.29, respectively. Soft coal wall bearing is mainly dispersed in the shape of “X” in its interior, forming intertwined pressure increasing and unloading zones, and most of the pressure increasing zones are at the edge of the outer end of the pressure relief zone, compression-shear type is the main failure form of the coal, and the middle and upper part of the coal wall in the height direction is easy to break and cause disaster. The coal wall of steeply dipping face partitioning migration features is obvious, and vertical displacement within 3.77 m from the coal wall is lower > middle > upper; after 3.77 m, it is upper > middle > lower; horizontal displacement is middle > upper > lower; coal migration volume in the middle region of the face is largest; and the coal wall instability has high frequency, wide influence area, and alternating evolution law.

Study on a Transparent Similar Rock-Anchoring Structure under Impact Tests and Numerical Simulation Tests

Interface slip is one of the main failure forms of an anchor structure, but the debonding slip process of rockbolt cannot be directly observed under impact load, so it is important to study the failure mechanism of the interface debonding of an anchor structure. For this purpose, a kind of transparent similar rock-anchoring structure and a new rockbolt impact load test system were developed. The debonding process of the anchor structure was carried out based on the system and Particle Flow Code (PFC) simulation test. The main conclusions are as follows: Axial force of rockbolt decreases progressively from the load end to the other end, but the shear stress of the interfaces increases at the early stage and then decreases. The majority of shear stress is at I interface compared to shear stress at II interface. The crack in the transparent sample occurs first in the middle of the sample, then extends to the local position of the two interfaces and finally penetrates all cracks, and the debonding failure mode is dual-interface mixed. According to laboratory tests and PFC simulation tests, the crack growth process can be divided into three stages. The results of the PFC simulation tests are similar to those of the laboratory impact tests of rockbolt.

Mechanism Analysis of Roof Deformation in Pre-Driven Longwall Recovery Rooms Considering Main Roof Failure Form

Pre-driven recovery rooms are used extensively for the removal of mining equipment and hydraulic supports in longwall coal mining. Roof stability is a crucial factor influencing the speed and safety of the removal of operators in pre-driven recovery rooms. The characterization of roof deformation mechanisms in recovery rooms under front abutment pressures is significant for surrounding rock control and stability evaluation. In this study, three different roof subsidence evaluation models, considering different main roof failure forms, were established. It was noticed that the main roof break position had a significant effect on recovery room roof sag. The breaking of the main roof above the main recovery room and protective coal pillar was found to be the main driving force for large roof deformations. Furthermore, field monitoring data of roof sag and coal pillar stress in the 15205 and 15206 panels of Hongliulin Coal Mine were analyzed. According to evaluation models and field monitoring data, we propose determination methods for the evaluation of recovery room roof sag and main roof break position. During the study it was found that the inversion results of the main roof break position of the recovery room in 15205 and 15206 panels were 4.2 m and 9.1 m, respectively, which are basically consistent with the results calculated by periodic weighting. The research findings provide a reference for the quantitative evaluation of recovery room roof stability and the design of support parameters and yield mining.

Failure analysis of shot-piston used in squeeze casting process equipment

The failure investigation has been conducted on shot-piston used in injection system of squeeze casting equipment to clarify its failure mechanism. The macroscopic morphology of failed shot-piston showed there were many network cracks on its upper-end surface while the cylindrical surface was seriously worn. Further studies were carried out on the two surfaces respectively. Firstly, the shot-piston upper-end surface was sampled. And the crack distribution and depth were observed. Then, the crack micromorphology was investigated by scanning electron microscope (SEM), and the sampling points inside cracks were analyzed by energy dispersive spectrometer (EDS). The results show the shot-piston upper-end surface produces thermal stress cracks due to the high-temperature thermal cycle, and oxidation occurs in the cracks. The same method was also used for the cylindrical surface failure mechanism analysis. Above all, the cylindrical surface was sampled and the wear morphology was measured. Afterward, the material composition of the bulge on the cylinder surface and the micromorphology were confirmed by SEM and EDS. The results demonstrate the main failure forms are abrasive wear and adhesive wear. The inconsistent thermal deformation of the shot-piston and shot sleeve caused changes in the fit clearance and resulted in friction and wear. Simultaneously, the metal solution and oxygen erode the shot-piston matrix through the furrow, accelerating wear and failure. According to the failure mechanism of different surfaces, shot-piston service life can be extended by optimizing the squeeze casting process, controlling the temperature gradient, and selecting the appropriate fit clearance, which has important engineering significance.

Stress Distribution and Failure Characteristics of Stope Overburden of an Inclined Coal Seam

The stress distribution, failure depth, and shape and range of overlying strata of the stope are important bases for the prevention of roof water hazards and determination of reasonable locations of roof roadways. Based on the hydrogeological data of the E9103 workface, FLAC numerical simulation software was used to establish a numerical calculation model of the overlying strata of the E9103 inclined coal seam, and the stress distribution and failure characteristics of the overlying strata were analyzed. The development height of the caving and water-flowing fractured zones in the overlying strata of the workface was determined. Results showed that the stress reduction area appeared above the goaf in the form of an “arched” distribution, and tensile stress occurred in the local area of the overburden. The overburden relief arch of the workface was symmetrically distributed along the advanced direction and asymmetrically distributed along the inclined direction, with the arch crown deflecting above the workface. The horizontal and vertical displacements of the overlying strata of the stope increased with the advancing distance of the workface. The horizontal displacement in the x -direction presented two obvious regions, and the critical points of the two regions moved forward with the advancement of the workface and showed a certain degree of symmetry. The horizontal displacement in the y -direction presented an “inverted bowl” distribution and increased with the advancement of the workface. The main failure forms of the overlying strata of the workface were a tensile and shear failure, and shear failure was dominant in the upper direction. The height of the overburden caving zone in the workface had little relationship with the advancing distance of the workface and increased slowly as the advancing distance of the workface increased. The development height of the caving zone is 7.2–18.13 m. The development height of the water conduction fissure zone increased rapidly with the increase in the advancing distance of the workface. When the advancing distance was equal to the length of the workface, the development height of the water conduction fissure zone was flat and basically maintained at a stable value. The development height of the water conduction fissure zone is 30.8–62.2 m. These research findings have important engineering importance for ensuring safe and efficient mining of E9103 workface.

Experimental and numerical study on multiaxial creep behavior of 16MND5 steel at 700℃

In-vessel retention (IVR) is an effective strategy of ensuring the structural integrity of RPV under severe accidents. In the IVR condition, due to the geometric discontinuity of pressure vessel, multiaxial creep is the main form of failure of RPV. Moreover, 16MND5 steel undergoes a phase transition from bainite to austenite. In order to study the multiaxial creep failure mechanism, creep tests on different notched bar are carried out at 700℃. The influence of grain boundary precipitation on creep behaviors was studied by micro-structural observation. Furthermore, based on the Kachanov-Robotnov continuous damage model (CDM), the term of activation energy Q is adopted in the newly-developed model as the correction parameter that is used to study the damage evolution and multiaxial creep behaviors of 16NND5 steel. Finally, the good agreement is achieved between theoretical prediction and experimental results.

Deformation and failure analysis of surrounding rock mass in deep buried tunnels subjected to excavation

With the rapid development of underground engineering, the construction of hydraulic tunnel is faced with complex geological conditions. Rock burst and deformation have become the bottleneck of engineering construction. The study of deformation and failure mechanisms of surrounding rock mass during the excavation of deep buried tunnel has become important for the field of underground engineering. The traffic tunnel of Shuangjiangkou hydropower station is studied to identify the failure mechanism of surrounding rock mass of deep buried tunnel. We introduced microseismic monitoring technology to delineate potential risk areas and reveal the space-time evolution of microfractures. The failure type of the surrounding rock is determined by source parameters. The relationship between surrounding rock deformation and excavation dynamic response is analyzed based on the geological and microseismic data. The results show that the 3D microseismic visualization model can realize the advanced detection of the internal damage of surrounding rock. The source parameters reveal that tensile failure is the main form of failure in the tunnel surrounding rock. Strong unloading and poor geological conditions are the main factors affecting the stability of surrounding rock mass. The study combines microseismic monitoring with field investigation, and then comprehensively evaluates the stability of the tunnel surrounding rock providing a reference for similar underground engineering.

Effect of the Position of the Boundary Rivets on the Quality of Riveted Single Strap Butt Joints.

Riveting is widely used in aircraft manufacturing. The strap butt joint is often used in the aircraft’s main bearing area such as the aircraft docking area. The connection quality affects the reliability and safety of the aircraft directly. To study the effect of the rivet position on the connection quality of the strap butt joints, this paper analyzed the distribution of stress around the rivet hole at different positions by the finite element method, and then further analyzed the influence of the different rivet layouts on the connection quality of the strap butt joints by experiments. The static load tensile failure test of the joints was carried out, and the obtained tensile strength and failure mode of the strap butt joints showed that the main static tensile failure form of the single strap butt joint is that the whole rivets is sheared and the connecting sheets are separated. By changing the layout of different rivets, the connection strength can be maximized by reducing the outer row spacing (ORSD) of rivets. The results can be used for reference in the design of the riveting structure of aircraft panels.

Interfacial Microstructure and Formation of Direct Laser Welded CFRP/Ti-6Al-4V Joint

Joining fiber reinforced polyether ether ketone resin matrix composite (PEEK-CFRP) with Ti-6Al-4V titanium alloy to form a composite structure is a promising manufacturing process. Huge difference of material properties is the biggies challenge to join them. Continuous laser welding process is conducted in this experiment to join the two materials. In this study, joints under different welding speeds were obtained. Mechanical properties and microstructures were observed, and the interfacial structures were tested. The results showed that fixed joint could be obtained. As the welding speed decreased, the tensile shear first increased and then decreased. The shear force reached a maximum value of 36.8 N/mm at the speed of 10 mm/s. The quality of joint could be observably affected by welding speed. The formation of bubbles, cracks, and anchor effect at the interface were the main factors affecting the mechanical property of joint. Thus, adhesion failure was the main failure form for CFRP fracture. Ti, Al and some other elements had been diffused across the interface, resulting in the formation of intermediate transition layer. The result of EDS, X-ray and XPS test indicated that CTi0.42V1.58 phase could be formed, and Ti at the interface could react with the oxygen and carbon of CFRP to form TiO2, TiO and TiC, forming a stable joint structure.

Effect of hygrothermal environment on properties of induction welding joint of carbon fiber reinforced polyphenylene sulfide laminate

The carbon fiber reinforced polyphenylene sulfide (CF/PPS) composite laminate was taken as the research object, and the induction welding method was used to weld the CF/PPS laminate. It was focused on the effect of hygrothermal on the welded joint performance of the CF/PPS laminate. The experimental results show that the PPS resin does not undergo chemical changes before and after moisture absorption. At room temperature, the shear strengths of the welded joints gradually decrease with the increase of moisture absorption time, and compared with the dry welded joints, they are reduced by 15%, 18%, 23%, 32%, and 38%, respectively. The wet stress increases at the interface of the stainless steel mesh, resin matrix and carbon fiber, which weakens the bonding performance of the welded joint interface, and affects the failure mode of the welded joint. Under the environment of 120℃, the shear strength values of the welded joints with different moisture absorption times decrease by 12%, 15%, 22%, 37% and 44%, respectively. High temperature and high humidity make the thermal stress and wet stress at the interface of the stainless steel mesh, resin matrix and carbon fiber greater, which aggravates the damage of interface bonding performance. Interface debonding is the main failure form of the welded joints.

Design and Performance Research of Flexible Drill Pipe Joint Based on Bionic Theory

Fatigue fracture is the main failure form of mining drill pipe joints, which directly leads to the occurrence of drill pipe drop accidents. Based on the principle of engineering bionics, the spine structure and kinematic behavior characteristics of cheetah were studied; the bionic design and trial production of drill pipe joints were carried out. For the bionic drill pipe joint, it separates the torsion transmission function from the connection function, and when the torsion transmission function of the joint fails, the connection function is still effective, so as to achieve the effect of “breaking the bones and connecting the ribs.” The mechanical and flow field properties of the bionic drill pipe joint were analyzed. Mechanical test results showed that, for the bionic drill pipe joint, the average tensile capacity was 555.48 kN and the average torsion capacity was 8914.13 N·m, which met the mechanical performance requirements. The flow field numerical simulation results showed that, when the drilling fluid velocity field and pressure field were stable and change evenly, there is no risk of leakage. The study results can provide a new research idea for the research and development of mine drill pipe joint with long life and antidropping function.

Failure behavior and influence of surgical tool edges in soft tissue cutting

Failure on the cutting edge of surgical tools can affect their repeated use and is an important issue that needs to be addressed. The influence of the cutting length and soft tissue type on cutting forces, surface morphology, surface roughness, corner radius and sharpness index of the cutting edges on surgical blades in the process of soft tissue cutting was investigated in this study and the failure behavior of the soft tissue cutting edge was discussed. The friction force and the corner radius remain relatively stable with increased cutting length, while sharpness index, surface roughness, cutting force and stiffness force increase. Biological materials have a significant impact on the sharpness index of the cutting edge ( p = 0.000 < 0.05). A cutting durability decay model based on sharpness index and a failure model, where the main failure form is tissue adhesion wear in soft tissue cutting, are proposed in this paper. The timely removal of the surface adhesion on surgical tools can effectively decrease rapid failure. A precise regression model of the relationship between cutting force and corner radius was derived under the condition of a stable cutting state (R 2 = 0.95), which connected the macro cutting force with the micro cutting edge structure. Anti-adhesion technology or sharper cutting edges are recommended to be adopted in surgical tool manufacturing to reduce the probability of adhesion failure to surgical tools.