Thickness Unevenness Research Articles

Comparative study of the strain and strain rate hardening mechanisms and its workability during hot deformation of TC4 titanium alloys

Localized thinning is one of the main defects in hot forming processes, which is determined by the hardening behaviour during deformation. This study focused on building a hot-workability map to prevent localized thinning in wide ranges (650–950 °C & 0.001–1 s−1) for industrial significance. Insights into the associated strain and strain rate hardening mechanisms were provided by visualizing the microstructure evolutions using both in-situ High-Temperature Laser Scanning Confocal Microscope (HTLSCM) and Electron Backscattered Diffraction (EBSD). Results show that the highest uniform strain, up to 0.250, is achieved in the viscoplastic region due to the cooperative strain and strain rate hardening, where dislocation slip, α/β transformation and grain sliding concurrently occur. Significant grain refinement is also achieved. The optimum forming condition was identified in the viscoplastic region and is further verified by forming an ultra-thin large bend component, reducing thickness unevenness from 18.6 % to 13.1 %. This research finding could aid in understanding the effects of strain and strain rate hardening on forming uniformity and further provide scientific guidance for industrial processing parameters selection, reducing localized thinning and hence scrap rates.

Numerical Analysis of Thickness Uniformity Improvement with Different Inlet Plate Numbers during APCVD Process

As the nanometer line width in the semiconductor industry further shrinks, the surface flatness requirements for atmospheric pressure chemical vapor deposition epitaxial silicon films have further increased. Through a series of numerical simulations, this study analyzes the use of inlet plates to solve the problem of uneven wafer thickness during atmospheric pressure chemical vapor deposition. The results show that without the inlet plate, the deposition rate is lower at the center of the wafer and higher at the edge of the wafer. Wafer epitaxy thickness uniformity can be improved when inlet plates are used. By adjusting the position of the inlet plates, this unevenness can be further improved. As the number of inlet plates increases from 0 to 3, the wafer thickness non-uniformity decreases from 12.5% to 1.8% respectively. When the number of inlet plates continues to increase, the thickness uniformity of the wafer can be further improved. When the number of inlet plates is 5, the thickness unevenness of the wafer reaches 0.7%.

Prediction of Collapsing Strength of High-Strength Collapse-Resistant Casing Based on Machine Learning

With the increasing complexity of shale gas extraction conditions, a large number of high-strength collapse-resistant casing is applied to the extraction of unconventional oil and gas resources. There are errors in the traditional API collapse strength formula. A high-precision and low-computational-cost model is needed for predicting the strength of high-collapsible casing. The key influencing factors of casing anti-collapse strength were determined as outer diameter, wall thickness, yield strength, ovality, wall thickness unevenness, and residual stress by analyzing the casing collapse mechanism. In response to the key factors mentioned above, a dataset was formed by measuring the geometric parameters of the full-size casing and collecting data on the results of the anti-collapse strength experiment, which was divided into a training set (70%) and a testing set (30%). Three machine-learning algorithms, a neural network, random forest, and support vector machine, were trained to predict the anti-extrusion strength. The correlation coefficient R2, root mean square error RMSE, and average relative MRE were used to evaluate the indexes for model preference evaluation. The results show that machine-learning algorithms have unique advantages in casing anti-collapsing strength prediction. Within which, the neural network prediction model has the best prediction effect, and its characteristics of high precision, low cost and high efficiency are more suitable for the prediction of casing extrusion strength. Its testing set R2 is 0.9733, RMSE is 0.0267 and MRE is 0.0782, and the prediction accuracy can reach 92.2% which is much higher than the API calculation result (63.3%). The network prediction model is suitable for casing anti-collapsing strength prediction and meets the actual prediction requirements.

Effects of the electric field at the edge of a substrate to deposit a Ø100 mm uniform diamond film in a 2.45 GHz MPCVD system

In this study, uniform diamond films with a diameter of 100 mm were deposited in a 15 kW/2.45 GHz ellipsoidal microwave plasma chemical vapour deposition system. A phenomenological model previously developed by our group was used to simulate the distribution of the electric strength and electron density of plasma. Results indicate that the electric field in the cavity includes multiple modes, i.e. TM02 and TM03. When the gas pressure exceeds 10 kPa, the electron density of plasma increases and plasma volume decreases. A T-shaped substrate was developed to achieve uniform temperature, and the substrate was suspended in air from Ø70 to 100 mm, thus eliminating vertical heat dissipation. An edge electric field was added to the system after the introduction of the T-shaped substrate. Moreover, the plasma volume in this case was greater than that in the central electric field but smaller than that in the periphery electric field of the TM02 mode. This indicates that the electric field above and below the edge benefits the plasma volume rather than the periphery electric field of the TM02 mode. The quality, uniformity and surface morphology of the deposited diamond films were primarily investigated to maintain substrate temperature uniformity. When employing the improved substrate, the thickness unevenness of the Ø100 mm diamond film decreased from 22% to 7%.

A novel method for evaluating the slurry coating characteristics of sized yarns based on the starch-iodine color reaction principle and image processing

The slurry coating characteristics of sized yarns directly impact warp weavability. Due to the damage to sized films, the conventional methods of detecting sized-yarn coating characteristics have drawbacks of low efficiency and poor repeatability. A novel detecting method of slurry coating characteristics was proposed based on image processing. Through the starch-iodine color reaction principle, a self-made dynamic image acquisition device was developed in this paper, in which the apparent images of starch-based sized yarns after color reaction were captured consecutively. The slurry coating percentage ( SCP), slurry coating depth ( SCD) and slurry coating unevenness ( SCU), respectively reflecting the sizing coating integrity, sizing coating thickness and thickness unevenness, were extracted by image processing. The effects of experimental parameters, including immersion time and concentration of I2-KI solution, on slurry coating characteristics were analyzed, and central composite design was adopted to optimize the stability of the test system. Sized yarns commonly used in textile mills were characterized by the proposed method. The experimental results indicated that immersion time of 3.56 min and I2-KI concentration of 0.11‱ (‱ represents that the mass of the solute is one ten-thousandth of solution) led to the optimal stability of slurry coating characteristics (the CV of SCP, CV of SCD and CV of SCU were 3.32%, 5.56% and 9.37%, respectively). The much lower CV of the proposed method compared with conventional ones confirmed that the method was useful for evaluating slurry coating characteristics.

Experimental investigations on the implosion characteristics of thin cylindrical aluminium-alloy tubes

Experimental studies are conducted to investigate the implosion characteristics of thin cylindrical aluminium-alloy tubes. The effects of various parameters that generate different responses on the implosion behaviours are investigated. Aluminium-alloy tubes are fabricated from a 6061-T6 material and designed in the range of 2.5–6.7 length-to-diameter ratios; wall thickness-to-diameter ratios are varied from 55 to 69. The geometric imperfection parameters, defined as the initial ovality and thickness unevenness, are considered. Two different pressurising media, i.e., water only and the combination of water and nitrogen gas are employed. In addition small- and medium-sized of pressure chamber are utilised to clarify the pressure drop after the ultimate strength reached. Furthermore, non-linear finite element analyses, benchmarked for quantitative validation and comparison of the imploded tubes, are conducted. The numerical benchmark quantities are initial ovality, thickness unevenness, and air-backed fluid cavity parameters. The results of these experiments indicated that the effects of combined water and nitrogen can reproduce a constant pressure environment similar as actual undersea conditions, but the combined pressuring media can reduce the pressuring rate.

Structural features of multifidus muscle in patients with degenerative diseases of the lumbar spine

Aim: to investigate the structural and functional changes in paravertebral muscles of patients with degenerative diseases of the spine based on histological and electron microscopic analyzes.Material and methods: histological and electron microscopic analysis of multifidus muscles of 49 patients (27 men and 22 women) was performed. Patients were on treatment between September 2015 and March 2018. The material was obtained during surgery for degenerative diseases of the spine: instability (9 patients), (11), (9), disc herniation (20).Results: dystrophic disorders of muscle fibers were detected. There were thickness unevenness, discoid decay, loss of transverse striation and polygonality, replacement of muscle fibers with fat tissue, proliferation of fibrous tissue, edema. Prevalence of adipose tissue was found in 20 % of patients with a disc 22.22 % with instability, 36.36 % with spondylolisthesis, 44.44 % with stenosis. The proliferation of connective tissue only in perimysium was defined in patients with a diagnosis lumbar disc herniation, in others – both in perimysium and in endomysium. At the ultramicroscopic level, in the postoperative material of the patients with and stenosis, in addition to intermyofibrillar edema and the violation of the architectonics of sarcomeres, as well as the structure and location of the mitochondria, focal necrosis of myofibrils were detected. Areas with a normal distribution of mitochondria were noted only in a group of patients with a disc herniation. In patients with a diagnosis of spinal stenosis violations of the ultrastructural organization of venules were found. This has a negative effect on nutrition and, accordingly, the functioning of a partitioned muscle.Conclusion: the greatest manifestations of dystrophic disorders of muscle fibers at the tissue and ultrastructural levels were revealed in patients with diagnoses of spondylolisthesis and spinal stenosis

Using fuzzy rule-based knowledge model for optimum plating conditions search

The paper discusses existing approaches to plating process modeling in order to decrease the distribution thickness of plating surface cover. However, these approaches do not take into account the experience, knowledge, and intuition of the decision-makers when searching the optimal conditions of electroplating technological process. The original approach to optimal conditions search for applying the electroplating coatings, which uses the rule-based model of knowledge and allows one to reduce the uneven product thickness distribution, is proposed. The block diagrams of a conventional control system of a galvanic process as well as the system based on the production model of knowledge are considered. It is shown that the fuzzy production model of knowledge in the control system makes it possible to obtain galvanic coatings of a given thickness unevenness with a high degree of adequacy to the experimental data. The described experimental results confirm the theoretical conclusions.

Research of the process of axisymmetric forming of thin-walled flat blanks into the conical parts with minimal thickness variation

In this paper, the method based on the process of forming a flat blank into the thin-walled conical part is proposed. The forming method is based on two stages. At the first stage, forming of the free portion of the blank is carried out until it fully contacts the conical surface of the punch. During this stage, thickness unevenness is created, which can be compensated during the second stage by the action of active friction forces. The shaping of the workpiece during the forming of the conical part is performed by thinning. The thinning increases with the increase of the penetration depth of the punch, i.e. the final part will be thinner, but its thickness variation will be reduced. This method allows achieving minimal thickness variation in the walls of the part.

Numerical analysis on the origin of thickness unevenness and formation of pits at GaN thin film grown by HVPE

In this study, we propose a 3D model for analyzing the fluid flow, mass fractions of reacting gases, GaN deposition thickness distribution and V/III ratio distribution at the GaN deposition surface in the multi-susceptor HVPE equipment. The GaN thin film is grown in the multi-susceptor HVPE equipment at 1213K and 1bar. The deposition thickness distribution from the calculation has been compared with the experimental results. Moreover, the standard deviations of deposition thickness of the films achieved from calculations and experiments have been compared. Besides, in the calculation results, we found that the V/III ratio at the GaN deposition surface increased from the center to the periphery and from low susceptor to high susceptor. Our calculation results have also been verified by 3D measuring laser microscope observation of the surface morphology of the GaN thin film. In according with the calculation results, the density of the pits also decreases from the center to the periphery as well as from low susceptor to high susceptor, demonstrating that the pit density at the surface of the GaN thin films could be reduced when the V/III ratio is increased.

Necking behavior of AA 6022-T4 based on the crystal plasticity and damage models

In order to analyze necking behavior with a continuum level approach, initial imperfection or bifurcation algorithm should be employed. The initial imperfection is arbitrary and has a great effect on the necking behavior of sheet metals. Most polycrystalline materials have natural imperfection such as orientation mismatches across the grain boundaries. In polycrystal plasticity, orientation mismatch is considered as material imperfection instead of geometric imperfection including thickness unevenness. The main idea of this study is to investigate the possibility that the stress concentration on a grain boundary (caused by orientation mismatch) works as imperfection and finally causes necking. For the consideration of stress concentration along grain boundaries, a crystal plasticity model was introduced in three-dimensional finite element analysis of a tensile test. A small region of a tensile specimen was divided into sufficient number of octahedral grains and each grain was discretized by fine tetrahedron elements. The same orientation angle was allocated for all the elements in each grain, but different orientations for grain by grain. Using this crystal plasticity-based analysis, stress concentration in the grain boundaries can be predicted. Also, four damage models based on the critical strain and stress were proposed to consider material softening due to void initiation and growth under the framework of crystal plasticity theory. The damage parameters for each model were determined based on the stress–strain relations obtained from experiment. Void nucleation, growth and coalescence behaviors during necking were reasonably predicted. Finally, the predicted necking behaviors of AA 6022-T4 were compared with the experimental results in terms of necking strain, deformed shape, and necking direction.

Simulation and Optimization on Dynamic Hydraulic Drawing for Spiral Bottom Shell Parts

The dynamic hydraulic drawing simulation is a valid method that reduces costs, increases quality and discovers hydraulic forming process problems.The simulation process of hydraulic drawing for spiral bottom brake shell parts with space surface feature was investigated and the optimal processing parameters were acquired by using Dynaform software. The results showed that model approaches, model methods, meshing and parameters setting were the foundation of hydraulic drawing simulation and the optimized control of holder force and fluid pressure were the key factors for preventing defects during hydraulic deep drawing. Meanwhile, the suitable blank shape was found good for reducing the defects of Wall Thickness Unevenness and oral flange earing, etc.

Magnetron-sputtered cobalt-based protective coatings on ferritic steels for solid oxide fuel cell interconnect applications

Co, Co–Mn (67:33 at.%) and Co–Cu (67:33 at.%) coatings were fabricated using magnetron sputtering on two kinds of ferritic stainless steels (Crofer22APU and F17TNb) in order to form spinel protective coatings on metallic interconnects for solid oxide fuel cells. Despite the thickness unevenness at different regions, dense metallic coatings were successfully applied onto all necessary surfaces of the channelled interconnect substrates. Upon oxidation, spinel oxide coatings with very low Cr content were formed, reducing effectively the Cr release. Among the three protective coatings, Co–Cu coating showed the lowest area specific resistance (<15 mΩ cm 2 at 800 °C).

Effect of processing parameters on the uniformity of adhesive meltblown web

AbstractThe influence of the main processing parameters, including the primary air pressure, the accessory air pressure, the melt throughput rate, and the die‐to‐collector distance, on the uniformity of adhesive meltblown web produced on the pilot‐scale melt‐blowing equipment with the added accessory device is investigated using weight measurement and thickness measurement. The effects of the process parameters on the web weight unevenness and the web thickness unevenness are similar, so both the weight unevenness and the thickness unevenness can be used to analyze the web unevenness. The results show that the web unevenness increases with the increasing melt throughput rate and the accessory air pressure; the web unevenness decreases firstly and increases later with the increasing primary air pressure and the die‐to‐collector distance. POLYM. ENG. SCI., 2008. © 2008 Society of Plastics Engineers

Dissolution behavior of the barrier layer of porous anodic films formed on aluminum studied by pore-filling technique.

Dissolution behavior of the barrier layer of porous anodic films formed on aluminum after immersion in sulfuric acid has been studied using re-anodizing (pore-filling) technique. The higher a forming voltage is, the higher the dissolution rate of a film. The barrier layer of films formed in phosphoric acid was divided into three layers according as dissolution rate and was dissolved most rapidly in a middle layer. The defects were detected after the dissolution of an outer layer as fine pores which passed through the barrier layer. The volume of the defects increased with increasing forming voltage. In films formed in oxalic acid, however, no such defects as above but thickness unevenness were detected in the middle of the barrier layer which was divided into two layers. The dissolution rates of inner layers of films formed in two electrolytes at different voltages were low and almost same. The dissolution rate is suggested to depend on both contents of incorporated anions and defects.