Shrinkage Holes Research Articles

Thermodynamics and energy properties of the lowest eutectic mixture of TNBA/MTNP

In light of the challenges posed by the low density, diminished energy levels, and shrinkage holes in the loading arise of the current cast-cured explosive liquid vehicle, TNT, the investigation of low-melting eutectic materials as potential substitutes for TNT has emerged as a focal point of research. By employing the solvent-nonsolvent method, the lowest eutectic mixture of TNBA(2,4,6-trinitro-3-bromoanisole)/MTNP(1-methyl-3,4,5-trinitropyrazole) was synthesized, distinguished by a moderate melting point and markedly elevated energy levels as compared to TNT. Comprehensive SEM, EDS, IR, XRD, and XPS analyses were conducted on the lowest eutectic mixture, substantiating the absence of any chemical interaction between TNBA and MTNP and affirming their exceptional compatibility. Moreover, an exploration into the thermal decomposition behavior and mechanism of the lowest eutectic mixture was undertaken, its mechanical sensitivity was tested, and its detonation performance was evaluated by EXPLO-5 software. The thermal decomposition parameters of the lowest eutectic mixture closely paralleled those of the precursor materials, with the thermal decomposition kinetics model function being identified as the Jander function. The impact sensitivity of the lowest eutectic was 48.1 cm and the friction sensitivity was 12%. Furthermore, the density of the lowest eutectic mixture surpassed 1.8 g/cm3, and its detonation velocity approached 8000 m/s, markedly surpassing the explosive performance of TNT.

DES-YOLO: a novel model for real-time detection of casting surface defects.

Surface defect inspection methods have proven effective in addressing casting quality control tasks. However, traditional inspection methods often struggle to achieve high-precision detection of surface defects in castings with similar characteristics and minor scales. The study introduces DES-YOLO, a novel real-time method for detecting castings' surface defects. In the DES-YOLO model, we incorporate the DSC-Darknet backbone network and global attention mechanism (GAM) module to enhance the identification of defect target features. These additions are essential for overcoming the challenge posed by the high similarity among defect characteristics, such as shrinkage holes and slag holes, which can result in decreased detection accuracy. An enhanced pyramid pooling module is also introduced to improve feature representation for small defective parts through multi-layer pooling. We integrate Slim-Neck and SIoU bounding box regression loss functions for real-time detection in actual production scenarios. These functions reduce memory overhead and enable real-time detection of surface defects in castings. Experimental findings demonstrate that the DES-YOLO model achieves a mean average precision (mAP) of 92.6% on the CSD-DET dataset and a single-image inference speed of 3.9 milliseconds. The proposed method proves capable of swiftly and accurately accomplishing real-time detection of surface defects in castings.

DEVELOPMENT OF A FOUNDRY TECHNOLOGY FOR OBTAINING A CAST PROTECTIVE MODULE BY LOST FOAM CASTING

Purpose. Development of a foundry technology for obtaining a hollow casting of a protective module by lost foam casting.
 Research methods. Computer simulation of foundry processes was used and practical experiments were carried out.
 Results. Based on the analysis of metal pouring processes using computer simulation, the hydrodynamic conditions for pouring the protective module casting with different gating systems were established. With the upper distributed gating system, filling occurs from the center to the edges. At the same time, the hydrodynamic pressure of the metal causes uneven filling of the walls of the casting, as a result of which a large metal flow front is formed. With the lower one-sided downpour system, the area of the flow front decreases, and the filling of the mold occurs evenly, which eliminates the possibility of sand collapse. The results of simulation of metal solidification processes showed that there are no shrinkage holes in the casting of the module, but there is a slight microporosity due to the construction of the casting.
 Scientific novelty. It was determined that the formation of a collapse defect in a casting with the upper gating system during lost foam casting occurs due to a large front of the metal flow, which leads to excessive release of gases and the formation of low vacuum conditions in the core parts of the mold, as a result of which the impact of the jet metal occurs local sand collapse.
 Practical value. The gating system and the overall technological process of obtaining cast protective modules from steel by lost foam casting were optimized.

Impact of Titanium Addition on Microstructure, Corrosion Resistance, and Hardness of As-Cast Al+6%Li Alloy

Aluminum-lithium alloys have the potential for use in aerospace applications, and improving their physical, mechanical, and operational characteristics through alloying is a pressing task. Lithium, with a density of 0.54 g/cm3, enhances the elastic modulus of aluminum while reducing the weight of the resulting alloys, making them increasingly attractive. Adding transition metal additives to aluminum alloys enhances their strength, heat resistance, and corrosion resistance, due to their modifying effect and grain refinement. The study aimed to investigate the impact of titanium content on the microstructure, corrosion resistance, and hardness of Al-Li alloys. Four alloys were prepared with varying amounts of titanium at 0.05 wt%, 0.1 wt%, 0.5 wt%, and 1.0 wt%. The results showed that the microstructure of the alloy was modified after adding Ti, resulting in a decrease in average grain size to about 60% with the best refinement at 0.05 wt% Ti content. SEM and EDS analysis revealed an irregular net-shaped interdendritic microstructure with an observed microsegregation of Al3Li compounds and other trace elements at the grain boundaries. The samples showed casting defects due to the high content of Li in the alloy, which absorbed air during casting, resulting in casting defects such as shrinkage holes. The corrosion resistance test results were low for the samples with casting defects, with the least resistance recorded for a sample containing 0.1 wt% Ti content, with more casting defects. The addition of Ti increased the microhardness of the alloy to an average of 91.8 ± 2.8 HV.

Laser welding of carbon-fibre-reinforced polyetherketone and 304 stainless steel: Cost-effective approach using prefabricated holes

Laser welding of carbon-fibre-reinforced polymers and metals has broad industrial applications. Although methods, such as manufacturing surface microstructures, have been developed to enhance the strength of laser welding, they have not been widely promoted and applied because of their high cost and complex manufacturability. In this work, an economical approach for laser welding of carbon-fibre-reinforced polyetherketone (CFRP–PEEK) and 304 stainless steel by fabricating holes on metal surfaces was investigated. The effects of prefabricated holes with diameters ranging from 0.3 to 1.5 mm were comprehensively studied. The economy of pulse equipment and the convenience and efficiency of the punching process make this method promising for large-scale industrial applications. Based on the optimised process parameters of the laser welding test, it was found that an appropriate prefabricated hole can increase the joint strength by nearly four times, which is comparable to the results of current mainstream research. The main mechanism for increasing the strength is the pyrolysis of CFRP–PEEK, which generates high-pressure bubbles; these bubbles then extrude the molten CFRP–PEEK into the prefabricated holes. The prefabricated holes further promote the heat dissipation effect of stainless steel and reduce the heat accumulation during welding. The molten CFRP concentrated in the prefabricated hole solidifies, avoiding solidification on both sides of the prefabricated hole. This difference in the solidification state greatly reduces the formation of shrinkage holes, which enhances the strength of the joint.

The effect of solvent on preparation of CH3 NH3 PbI3 photodetectors via an antisolvent-free method.

During the fabrication of lateral-structured photodetectors based on CH3 NH3 PbI3 film, antisolvents represented by toluene are usually used to accelerate the crystallization of perovskite. Using antisolvent not only leads to the formation of shrinkage holes at the bottom of the perovskite layer, but the toxicity of antisolvents would also hinder the industrial preparation of perovskite devices. An antisolvent-free method is a possible solution to avoid these problems. Here, we report a lateral-structured photodetector based on an antisolvent-free method. The lateral photodetector exhibited a high responsivity of 1.75 A⋅W-1 and specific detectivity (D*) of 3.54 × 1012 Jones. In particular, the results indicated that the solvent had an influence on perovskite film morphology, crystallization, and device performance. The prepared CH3 NH3 PbI3 film presented needle-like crystals and low performance with single precursor solvent N,N-dimethylformamide (DMF). In comparison, appropriate mixing of dimethyl sulfoxide (DMSO) could improve the morphology, crystallization, and performance of the film. In addition, the solvent volume ratio of the precursor had a profound effect on the performance of the as-prepared photodetectors. At a DMSO:DMF volume ratio of 5:5, the as-prepared film had massive perovskite crystals and fewer defects, resulting in optimal device performance, which can be explained by Urbach energy.

The simulation of mould metallurgical behaviour under electromagnetic stirring for vertical large bloom

ABSTRACT According to the mould electromagnetic stirring of vertical round billet continuous casting, a three-dimensional mathematical model of electromagnetic field was established to study the distribution of magnetic field in the mould. On the centre cross section of agitator, the distribution of magnetic flux density is small in the centre and large in the edge, in the centre longitudinal section, the maximum value of magnetic flux density at the lower edge of the mould. The influence of electromagnetic parameters on the flow field and temperature field in mould was studied. When the section of round billet is 800 mm, the current intensity is 380 A and the current frequency is 3 Hz, and the proportion of equiaxial crystal is up to 43.6%. The central shrinkage hole, central crack and central porosity are all less than grade 1, and there is no white band, the stirring intensity of M-EMS is relatively ideal.

Metallography of non-metallic inclusions in pipe metal and impact assessment of defect structures on non-destructive testing outcomes

Low carbon steel pipes represent a core component in the gas pipeline system, so it is necessary to improve constantly diagnostic operations and assessment methods of their technical state. Studies on objects operated in diverse conditions within a long period provide reliable data on the real behavior of materials. A key issue is the investigation of characteristics and behavior of products with primarily incorporated defective structures undetected while manufacturing and constructing. It is difficult to forecast the behavior of such defects, in addition, considerably more work need to be done to determine their development, detection methods, and more importantly, their hazards. The reported study investigates the phases, structure and sizes of inclusions detected in the defective pipe metal in the natural gas pipeline. The property that characterizes defects of interest is their concentration within one pipe section in combination with diverse thickness, composition, and location in the pipe wall. Defects are found at various depths, forming one, two and more layers. The difference in structure and phase composition is outlined. The research has pointed out principal inclusions represent fragments of charge materials — fluorite and broken fireclay brick, a number of defects result from casting defects, e.g. gas bubbles and shrinkage holes. Non-destructive ultrasonic testing is implemented; the importance of thickness and structure of inclusions for measurement data has been realized.

Processing and characterizations of polycarbonate/alumina nanocomposites by additive powder fed friction stir processing

The powder fed friction stir process (FFSP) is a new and attractive solid-state manufacturing technique that enables the fabrication of polymer matrix nanocomposites (PNC). Herein, we present the fabrication of polycarbonate (PC)-based nanocomposites by in-situ injection of colloidal alumina nanoparticles (<100 nm) into the plasticized polymer under stir friction of a steel tool. Microstructural features and mechanical durability of the prepared nanocomposites were studied. The mechanical properties of the processed materials including hardness, tensile strength, flexural strength, and impact energy were elaborated. The tensile strength of PNC in the longitudinal direction was ~73 MPa, which was higher than the PC matrix by 109%. However, a lower bending strength (~48 MPa) compared with PC was measured. Fractographic studies determined the presence of mist patterns on flexural samples and crack growth from shrinkage holes and river patterns. The distribution of Al2O3 nanoparticles was found to improve the impact energy in both transverse and longitudinal directions by 111% (~28 kJ/m2) and 127% (32 kJ/m2), respectively. Crack deviation by the hard inclusions was found to be the mean mechanism of enhanced impact resistance.

Study on the effects of tool tile angle, offset and plunge depth on friction stir welding of poly(methyl methacrylate) T-joint

The effects of tilt angle (TTA), plunge depth (TPD) and offset (TO) of tool in friction stir welding of poly(methyl methacrylate) T-joint were investigated. To understand better the effects of process parameter, thermomechanical simulation of joint was assessed. The results seem to show that at higher TPD and TTA, frictional heat increases. Woven tissue structure joint line forms after friction stir welding of poly(methyl methacrylate) sheets. The distance of woven layers was affected by TPD and TTA, while TO do not significantly affect heat generation of joint. The best material flow and adequate heat are generated at 0 mm TA, 2° TTA and 0.2 mm TPD, respectively. The highest flexural and tensile strength of friction stir welded joint were approximately 93% and 90% of as-received poly(methyl methacrylate), respectively. Crack forking was detected on the fractured surface of flexural samples and crack path was detected in the vicinity of shrinkage holes at fracture surface of tensile samples. These holes and degradation of poly(methyl methacrylate) during friction stir welding process decrease strength and hardness of the joint.

Centerline inhomogeneity of flat products

Defect free casting requires an excellent accordance between steel properties being cast and the technological parameters, especially from the aspect of inner quality and homogeneity of cast products. Typical serious defects of cast slabs is the centerline segregation (CLS). The centerline segregation in slabs develops in a very complicated way, the main factors influencing the CLS pattern are the macrosegregation and the shrinkage of solidifying melt in the mushy area. The centerline section of the slab can be characterized by different chemical composition compared to the average composition and it can contain shrinkage holes, discontinuities and inclusions. In the hot rolling process the complex shape of interdendritic holes will be modified depending on the strain applied. In chemical composition the difference remains and it can be identified even after the soaking period (over 1050 °C). As an example, the center part of an St52 grade hot rolled heavy plates and strips containing CLS can be characterized by a carbon content of 0,3-0,5 wt% and manganese content of 1,7-1,9 wt%. The segregation level – including the carbon content – can hardly be decreased by post heat treatment or annealing.

Investigation on rock breaking for sandstone with high power density laser beam

High power density laser was applied during rock breaking for sandstone with different laser parameters. The fracture morphologies and quantitative characterization as well as the parameters on specific energy and rate of perforation were analyzed. It was found that a complex crack net structure was formed and the cracks area and length on the surface of sandstone specimen almost increased linearly with the number of laser perforation. Furthermore, the diameter and depth of laser perforation, the maximum width of cracks, the maximum depth and total circumferential length of side cracks increased with laser power and laser irradiation time. The experimental results demonstrated that the SE values gradually decreased with laser power while the ROP values increased. However, the SE values of sandstone by laser perforation presented a trend of first increase and then decrease, while the ROP values decreased gradually with laser irradiation time. A smooth glaze layer was formed on the inner wall of the laser perforation, where there also was plenty of shrinkage hole. Obvious cracks were generated and propagated along the inner wall. Typical brittle fracture occurred with the mix fracture mechanisms of intergranular fracture and transgranular fracture.

Experimental and thermomechanical study on FSW of PMMA polymer T-joint

The aim of this work is thermomechanical and experimental study on the effect of tool rotational and traverse speed on friction stir welding of PMMA T-joint. Development of temperature profile in the joint region was measured and compared with the results of thermomechanical modeling and tensile. Moreover, flexural and hardness tests were carried out for all samples. The results show that the highest tensile (~ 84% PMMA strength) and flexural (~ 93% PMMA strength) strength can be obtained at a 1600 rpm tool rotational speed and 25 mm/min traverse velocity. In these parameters, smooth surface and defect-free joint were produced. Fractographic studies of weldments indicate fracturing in brittle mode. Hackled regions in the tensile test on fracture surface and crack branches in flexural fracture surface were observed, showing that the PMMA shrinkage holes play crack initiation role in all of these phenomena. According to the results, the lowest hardness of stir zone was on the joint which was welded with 1600 rpm and 25 mm/min speed (75.5 Shore D) and highest hardness of stir zone was on the joint that was welded with 1000 rpm and 50 mm/min speed (85.6 Shore D).

The Quality Inspection and Defect Repair for Marine Anchors

Aim at the surface defects found in the quality inspection of marine anchors, structural features of anchors and factors affecting the forming process were analyzed, the typical defects found in the quality inspection of ship anchor were mainly studied, including cracks, blowhole, shrinkage hole, slag, sand casting residual stress and etc., the reasons of various surface defects were analyzed base on an example of stockless anchors, and several aspects of defect repairs focused on are pointed out.

Microstructure evolution during remelting of high solid fraction ZL101 alloy

This work deals with the reheating process for semi-solid thixoforming of ZL101 (AlSi7Mg) alloy. The semi-solid state can decrease the viscosity and the resistance while sheared because of the evolutional behavior, which is characterized by a solid-like behavior at rest and a liquid flow during shearing. The microstructure evolution of ZL101 alloy at different temperatures from 540 to 580 °C has been studied. Results show that the eutectic temperature can affect the transformation speed of semi-solid structure. Semi-solid microstructures with high solid fraction can be obtained by controlling the reheating time in less than 20min, while at the temperature lower than the eutectic temperature it needs more than one hour. Another character of semi-solid ZL101 alloy is the segregation of microstructures in semi-solid state, in which the liquid phase between the solid phases can flow freely and lead to the shrinkage of the sample during the heating process. As the holding time goes on, more shrinkage holes appear and change the surface of the specimen. These shrinkage holes are replenished by the liquid phase during compression deformation, resulting in the segregation of the components.

Numerical Analysis of Modes of Induction Weld Deposition of Valve Tappets of Motor Vehicles

The work is devoted to the reduction of defective weld deposition zone of the pusher, as well as the reduction of the number of defects such as low density of metal, pores, shrinkage holes. For the numerical analysis of the weld deposition process the 3D models were built and the required characteristics for the fused surface of the workpiece were set. The preheat temperature is set from 500°C to 1300°C, the deposited layer of cast iron with thickness of 6 mm the temperature of weld deposition is set as 1250°C, for cooling model the properties of water temperature of 20°C were applied. In the process of numerical analysis of the existing technological process of weld deposition the interrelation between the mode of technological process of welding, temperature of preheating of the workpiece and the size of the defective area of the deposited layer was established. According to the results of numerical analysis using statistical sequential analysis the mathematical model of the dependence of the size of defect-free area of the deposited layer from the preheating temperature of the workpiece of pusher was built. It was found that the lowering the temperature of preheating of the workpiece has a positive effect on the increase in the defect-free layer of deposited metal.

Defect Susceptibility of Tensile Properties to Microporosity Variation in As-Cast Al–xSi Alloys

The defect susceptibility of tensile properties to microporosity variation in as-cast Al–xSi (x = 2, 5, 8, 11) binary alloys was investigated in relation to the effective void area fraction, which includes the area fraction and the size distribution of the pre-existing micro-voids and damaged eutectic Si particles. The area fraction of eutectic Si particles and Si colonies increases with increasing nominal Si content, and the typical morphology of micro-voids changes from shrinkage hole type to blow hole type as the Si content increases. The tensile properties of Al–xSi alloys depend on microstructural characteristics, including the nominal area fraction of eutectic Si particles and eutectic Si colonies, the width of the pro-eutectic Al matrix, and the variation in microporosity. The defect susceptibility of ultimate tensile strength and elongation is estimated by the nominal area fraction of eutectic Si colonies rather than the nominal Si content. The relative contribution of the eutectic Si particles to the effective void area fraction can be described using a modified constitutive model that may confirm that the damage evolution of the eutectic Si particles influences the tensile properties of Al–xSi alloys.

Research into water-soluble salts in efflorescent pottery during long-term storage in a museum

Ancient pottery stored in northern Chinese museums is apt to powder during long-term storage. A detailed investigation of the efflorescent products of such pottery was performed to shed light on the role of water-soluble salts, a type of curing-salt-laden colloidal substance that shows smooth edges and shrinkage holes containing Cl−, NO2−, NO3−, SO42−, Na+, K+, Ca2+, etc., in pottery efflorescence. For comparison, recent specimens of pottery, buried soil and storeroom dust were characterised as well, demonstrating that, in this samples, water-soluble salts mainly originated from the surrounding atmosphere.

Simulation study on the centrifugal casting wet-type cylinder liner based on ProCAST

The casting defects that appear the inside surface of a wet-type cylinder liner (WTCL), such as macrosegregation and shrinkage holes, are important factors that affect the quality of the WTCL produced by centrifugal casting. To reduce these defects, a model of centrifugal casting WTCL based on the ProCAST software was constructed in this study, and the simulated result was used to optimize the casting process. The temperature field of the casting WTCL was simulated based on actual solidification, and the solidification process and casting defect were analyzed. Results show that the simulated temperature field is in accordance with the actual process and the casting defects appear in the final solidification zone and inside the sub-surface near the thick-wall side. These defects were later revealed on the surface after machining. The factors that affect the temperature field and the solidification process, such as the cooling-down method, mold structure, coating material, and coating structure, were also analyzed. Based on these analyses, an improved method was proposed.

A Three Dimensional Model to Characterize the Centerline Segregation in CC Slabs

In this investigation the formation of centerline segregation and shrinkage holes in the final stages of solidification during the continuous casting process of slabs is described. Therefore experimental and theoretical investigations of the melt behavior during the solidification are carried out. Based on these results, a model is presented to explain the formation of V‐shaped segregation and core porosities caused by the restricted flow of melt through the mushy zone in slabs. The theoretical explanation is manifested by various observation, calculations and analyses by electron microprobe mappings. The main results are that V‐segregation forms in quasi periodical frequency in longitudinal direction within continuous cast slabs. The areas of formation seem to be independent, like little billets lying side by side in one slab. Consequential a three dimensional model about the behavior of the liquid melt in the final stages of solidification is designed.