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Career exploration, as the antecedent variable of college student's career choice and employment, guides for the construction of their career. Based on the theory of social cognitive career, this study explores the formation mechanism of career exploration from three aspects: personality, family and university. Through a multi-stage investigation of 980 college students from 16 colleges and universities on Chinese mainland, it is found that: (1) Proactive personality positively affects career exploration; (2) College students' self-efficacy plays a mediating role between proactive personality and career exploration; (3) Teacher support and parental support strengthen the positive effect between self-efficacy and career exploration; (4) Both teacher support and parental support positively moderate the indirect influence of proactive personality on career exploration through self-efficacy. This study tries to provide practical guidance for college students to engage in career exploration and career construction from a pluralistic perspective.

Working tooth depth is the key factor of affecting the transmission of motion and power for gear pair, which is closely related to the tooth depth of gear. To reveal the growth law of the formed teeth in the cylindrical gear rolling process with axial infeed, a sliding ratio model and contact stress model between tooth profiles of rolling die and workpiece were firstly derived based on the characteristics of the gear pair and rolling process with axial infeed. Rolling of cylindrical gears with module of 1.75 mm and pressure angle of 20° was then taken as an example to verify the above-mentioned models, and the influence of the working pressure angle, number of teeth of workpiece, and rotational speed of rolling dies on the effective tooth depth of the workpiece were analyzed by using finite element simulations (FES) and experiments. The results show that the effective tooth depth of the formed workpiece increases with the increases of the addendum modification coefficient of the rolling dies, number of teeth of the workpiece, and rotational speed of the rolling dies. The sliding ratio and contact stress decrease with the increases of the addendum modification coefficient of the rolling dies and number of teeth of the workpiece. Moreover, the effective tooth depth of the workpiece formed by the rolling dies with addendum modification coefficient of 1 is increased by 7.41% compared to that formed by the rolling dies with addendum modification coefficient of the 0.

Large extrusion container (EC) is the key part of an extrusion machine, and generally it depends on shrink fitting of multi-layers to boost its strength. Because of the harsh condition of high temp...

INTRODUCTION In order to avoid large neck scar caused by conventional lateral neck dissection. We have explored and introduced endoscopic lateral neck dissection (IIA, IIB, III, and IV) using a breast approach. Now, we summarized and shared the outcomes of the first 24 cases. MATERIALS AND METHODS All the patients were treated in our institute from January 2017 to May 2018, and followed-up for more than 1 year. The details of patients and this technique have been summarized and analyzed retrospectively. RESULTS A series of first 24 cases were successfully managed with this technique, and no cases were converted to an open approach. Among these 24 patients, levels III + IV dissection had been performed in 6 patients and levels II+III+IV dissection had been performed in 18 patients. The mean age, body mass index, and sex were 39.3±10.5 years old, 24.1±3.5, and 2 male/22 female, respectively. The average operative time of total operation and lateral neck dissection was 238.8±37.2 minutes and 128.8±21.1 minutes, respectively. The mean dissected lateral lymph nodes were 5.9±2.2 (level II) in 18 cases and 15.9±3.9 (levels III+IV) in 24 cases. In addition, with no severe complications to date, such as asphyxia, main nerves injury (cervical plexus, vagus nerve, etc.), and permanent hypoparathyroidism, nor permanent recurrent laryngeal nerve injury, and so on. However, unexpectedly, had some mild and common complications like transient hypocalcemia in 4 cases (16.67%), transient horse 1 case (4.2%), controllable lymphatic leakage in 2 cases (8.3%), and controllable jugular vein injury in 2 cases (8.3%). One year after the operation, 1 case found lung metastasis but no local recurrence. In other 23 patients, no recurrence/metastasis and the average of serum thyroglobulin is 3.2±3.8 ng/mL. CONCLUSIONS This technique can yield adequate oncological dissection for selected patients. Endoscopic thyroidectomy along with lateral neck dissection using a breast approach may provide an option for selected patients who favor avoiding a visible neck incision.

Leveling process is usually used to minimize the plate defects including flatness imperfections and uniformity of internal stress in the plate industry. Roller intermeshes are important parameters in the leveling process to ensure the high-quality leveled plate. Some current researches treat the plate as a simple beam and ignore the stress superimposed effect to study how to set the roller intermeshes. This article presents an analytical optimization model to search the optimal entry and exit intermeshes for each incoming plate with consideration of the relationship between the roller intermeshes and bending curvatures during the whole leveling process. The optimization model was solved and the results were verified with production data. The relationship between the optimal roller intermeshes and plate thickness, yield stress, and Young’s modulus were discussed in details. It was found out that the roller intermeshes can be set the same for different incoming plates but with equal elastic limit curvature. A four-dimensional database of optimal roller intermeshes about different elastic limit curvature, expected plastic strain ratios, and roller spaces was built. The roller intermeshes can be quickly tracked in less than 1 s as long as the thickness, yield stress, and Young’s modulus of incoming plate and roller space are given according to the database so that it can be used effectively on the leveling production line.

Gear roll forming process is an innovative near-net-shape gear manufacturing technology for efficient manufacturing, high material utilization rate, high products strength, and outstanding surface quality. The profile of the Tooth of the Rolling Tool (TRT) has a direct impact on its strength/stiffness which further affects its life duration and the accuracy of the formed products. Research has been carried out to design the involute curve of TRT, however, the transaction curve of TRT which also has a significant impact on tooth strength and service durability remains to be designed and optimized in order to further improve the rolling performance. In this paper, an elliptical gear tooth root transaction curve is proposed to replace the traditional fillet curve for the enhancement of tooth bending performance. The maximum root stress and stiffness of the gear tooth with elliptical transaction curve are calculated and compared to the standard profile with different parameters (modulus, pressure angle, and coefficient of bottom clearance). The results show that proposed elliptical tooth reduces the maximum root stress and increase the strength and stiffness of TRT especially significant for rolling tools with small number of teeth and coefficient of bottom clearance.

Gear rolling process is an advanced forming technology in which the rolling die extrudes the preform material to flow plastically and finally form desired gears, and the preform dimension has a decisive impact on the quality of the final formed gears. To further explore the influence of tooth-tip defects on the tooth height of the formed gears in the forced throughfeed rolling process, and ensure the quality of the formed parts, a new computational method for the preform dimension was firstly proposed. A growth coefficient model based on the effective top circle of the formed gears was also given. Then, the dependence of the effective top circle size in regard to geometric parameters and material of the formed gears such as the number of teeth, module, and pressure angle were explored by the established model and finite element analysis (FEA). Finally, the experimental results were displayed to verify the proposed computational method and theoretical model. The results show the growth coefficient increases with the increase of the number of teeth and module, and decreases as the pressure angle increases. Moreover, the material with better plastic deformation ability contributes to improving the growth coefficient. Additionally, the proposed new method and theoretical model for preform dimension calculation could be adopted in the gear rolling.

In this work, a time-variant performance measure approach is proposed by searching the minimum performance value during the time period. A modified directional step method is proposed by obeying a search strategy that each iterative value should be smaller than that of previous one. With this strategy, the time-variant minimum performance target point can be quickly found in each inner loop. The proposed method is applied to three numerical examples. The results are compared with other two existing methods, which verifies the robust accuracy and effectiveness of the proposed method.

The cylindrical die forced throughfeed rolling process for gears was proposed to overcome an end-effect behavior of the standard radial-feed gear rolling process which can result in pitch variation and excessive axial end-flow. In the rolling process, the workpieces are pushed through the gap of the rolling tools to form the gear teeth. Understanding of material flow is important for grasping the cause of defect formation and improving the quality of formed gears. In this paper, the material flow behavior of the gear forced throughfeed rolling process was studied on the flow velocity and displacement of key locations by using finite element analysis (FEA). The experiment was also conducted and its blank was sliced to thin pieces, and the grid pattern (GP) was utilized to track the trajectory of flowing materials. The results show that the end-flow is located at the root rather than the tooth crest of the formed workpiece, because the compressive forces from rolling tool mainly take effect at the root of the formed workpiece. The asymmetry of circumferential flow displacements with respect to the gear teeth results in the asymmetrical flanks defect, and this is due to the meshing between teeth of rolling tool and workpiece. The local displacement in the radial direction is larger than that in the circumferential direction.

Though modeling material cyclic plasticity in a probabilistic way can yield a more accurate result than deterministic modelling method, it is quite hard to perform uncertainty quantification for all the material parameters. In this paper, Sobol’s global sensitivity analysis is applied to cyclic plasticity model to investigate how the variation of these parameters affect fatigue reliability evaluation. A machine learning algorithm is proposed to improve the computational efficiency for failure probability assessment. The results of global sensitivity analysis show that fatigue damage parameters, elastic modulus and initial yield stress are very influential to fatigue reliability analysis while others are not.

The existing step size methods aim to success in the convergence of searching the minimum performance target point in the reliability analysis. However, these methods cannot guarantee that the performance function value is smaller than that of previous point. This results in the redundant computation during the search process. In this paper, a new step method called hybrid directional step method is proposed to improve the efficiency of search process. The proposed method can keep the performance function values of iterations presenting a decreasing sequence and quickly converge to the minimum performance target point. The proposed method is compared with some existing methods through several numerical examples. The results show that the proposed hybrid directional step method presents good robustness and more efficient computation in practical application.

Roll-forming process is an innovative manufacturing technology for the near-net-shape production of high-performance gears. Outstanding surface quality, high material utilization rate and short process chain are the essential merits of this process. The geometry of rolling tool has a significant impact on its lifetime and the quality of formed gears. In this paper, analytical models with consideration of geometric parameters of rolling tools (cone angle, tooth depth and addendum modification coefficients) were proposed to investigate the forming force, root stress of rolling tool, rabbit ear defect and scratches on tooth flank. Then, an example was studied by using the proposed models, Finite Element Method (FEM) simulation and experiments. The results show that the optimized geometric design of rolling tool will not only reduce the deflection and root stress of rolling tool’s teeth, but also eliminates the scratches on tooth flank of the formed gear. Moreover, the positive addendum modification design of rolling tools also contributes to reduce the height of rabbit ear in the roll-forming process with axial-infeed.

AISI H13 (4Cr5MoSiV1) is one of the commonly used materials for extrusion tool, and it suffers from fatigue–creep damage during the hot extrusion process. Stress-controlled fatigue and creep–fatigue interaction tests were carried out at 500 °C to investigate its damage evolution. The accumulated plastic strain was selected to define the damage variable due to its clear physical meaning. A new fatigue–creep interaction damage model was proposed on the basis of continuum damage mechanics. A new equivalent impulse density for fatigue–creep tests was proposed to incorporate the holding time effect by transforming creep impulse density into fatigue impulse density. The experimental results indicated that the damage model is able to describe the damage evolution under these working conditions.

Gear roll-forming process demonstrates an innovative energy-material saving and high efficiency forming technology for the powertrain gears. The pitch error in the initial stage has significant impact on the pitch deviation of the formed gears and the lifetime of the rolling tools. In this paper, an analytical model was proposed for predicting the pitch error with consideration of geometric relations and process parameters. Then, the impact factors related to the rolling tools, workpiece and process were analyzed based on the proposed model. To verify the model, Finite Element Method (FEM) simulations and experiments were conducted. The compared results show that the proposed model can well predict the pitch error in the initial stage. Moreover, the root causes of pitch error were revealed and its influence factors were also discussed. This research will lead theoretical foundation for reducing the pitch error in the gear roll-forming process.

In this paper, a systematic framework has been proposed to simulate the structure’s fatigue life scatter. At first, cyclic plastic model coupled with fatigue damage is employed for fatigue life prediction. To consider variability in material, a parameters’ sampling strategy has been proposed by modeling Coffin-Manson parameter’s uncertainty. Then support vector machine combined with Monte Carlo simulation is used to assess structure’s failure probability. The method is modified by subset simulation when facing small failure probability problems. In the end, a numerical example of three-layer extrusion container is given for demonstrating the sampling procedure of material variability when experimental data of material is limit.

Extrusion is an efficient hot working process to aluminum production and AISI H13 (4Cr5MoSiV1) as the main material of extrusion tool suffers from fatigue and creep damage due to its extreme working condition. A new mean plastic strain life prediction has been proposed based on the energy method. In addition, statistical analysis is also taken into consideration to complement this physic-based model due to other unmeasured and unknown exogenous influences. To validate the model, a series of AISI H13 fatigue and fatigue–creep tests were conducted at 500 °C close to the practical aluminum extrusion process. The strain-controlled tests were used for obtaining the parameters, while the stress-controlled tests were utilized for validating the proposed model. It shows that the model predictions were in good agreement with the experimental results.

Hot extrusion is one of the most commonly used manufacturing methods for metal plastic deformation, and the consumption of extrusion tooling is considerably high due to its fatigue damage under cyclic serving condition. Hot-work tool steel AISI H11 is one of these typical materials employed in extrusion tooling. This work is dedicated to calculating the stress/strain state of AISI H11 and predicting its lifetime at high temperature 500°C by building a unified constitutive model coupled with Lemaitre's damage law. Tensile tests and strain/stress reversed cycling tests have been conducted at 500°C to investigate mechanical properties and damage evolution. A unified constitutive model with Armstrong-Fredrick/Ohno-Wang kinematic hardening rule and a new proposed isotropic hardening rule is built; Lemaitre's damage law is employed as well. Parameters are determined based on tests and are temperature dependent. Finite element simulation of the deformation behaviour and fatigue lifetime is implemented into commercial software ABAQUS Standard v6.14-2 with user material subroutine to validate the proposed method. The comparison shows good agreement with experimental results, and this part of work is essential and crucial to subsequent structure analysis.

AISI H11 (X38CrMoV5-1) hot-work tool steel is widely used for making extrusion tools because of its good mechanical properties at high temperature and moderate cost. To predict its lifetime, an energy conservation-based model was proposed in this paper by introducing the damage rate, which is expressed as the product of damage force and plastic strain rate. The strain-controlled low-cycle fatigue tests were conducted to obtain the parameters of the proposed model, while the stress-controlled low-cycle fatigue tests were used to validate the proposed model. The results demonstrate that the proposed model is accurate and reliable. Furthermore, the local misorientation was investigated by electron backscatter diffraction to analyse the correlation between the microstructure evolution and the cyclic behaviour, and crack propagation behaviour was identified.

The effect of aging treatment before extrusion on microstructure and mechanical properties of Mg-6Zn-1Mn alloy was investigated. Results showed that the existence of dispersive fine MgZn2 particles before extrusion promoted dynamic recrystallization in subsequent extrusion process and leaded to fine microstructures (grain size 1∼2 μm). The rod-shaped and plate-shaped precipitates in aged alloys transformed to fine and dispersed spherical precipitates after extrusion process. With aging and extrusion treatment, ZM61 alloy showed an outstanding tensile strength and elongation balance (YS 281 MPa, UTS 378 MPa and elongation 19.3%); compressive yield strength increased from 148 MPa to 259 MPa. The tension–compression yield asymmetry was reduced at the same time. The strengthening effect of aging treatment before extrusion in ZM61 alloy proved in this paper provided a new method for the design of relatively inexpensive high-performance magnesium alloys.

Most of the researchers are focusing to bring automation in mechanical systems. So, current research work presents a mechatronic system called active hydrostatic journal bearing that is a higher demand of fast-growing industrial needs. The objective is to improve the dynamics and static characteristics of hydrostatic journal bearing. To achieve the objective, a feedback servo controlled system is presented. A mathematical model is proposed for newly proposed active hydrostatic journal bearing with servo control. A comparison has been performed between the active hydrostatic journal bearing and traditional/conventional hydrostatic journal bearing under the influence of different dynamic conditions of load, viscosity, speed, and pressure. The results demonstrate that proposed active hydrostatic journal bearing has better performance, including controllability, stability, faster response, higher stiffness as well as better disturbance rejection. To further enhance the performance of proposed active hydrostatic journal bearing, two different control strategies are proposed such as proportional–integral–derivative and intelligent control. The results show that fuzzy logic–based intelligent control has faster response, greater amplitude reduction, and good stiffness against load. So, it shows that role of active lubrication in hydrostatic journal bearing will have potential applications in high load and high speed.