Mechanical Theory Research Articles

Design and cooling of permanent magnet generator in MW-class space closed Brayton cycle system

The closed Brayton cycle (CBC) system is a prime energy conversion technology to convert heat from the reactor to electric power for space missions due to its light weight, compact and stable operation. The CBC system incorporates a permanent magnet generator (PMG) mounted on the CBC shaft with the turbine and compressor. To ensure safe operation of the CBC system, a small fraction of the working fluid is used to provide the required cooling. In this study, four different cooling schemes used in CBC system are concluded and the key dimensions of the PMG are obtained through mechanical design theory and electromagnetic theory. Comprehensive research on the electromagnetic field and loss calculation is then performed. Furthermore, the cooling paths of the PMG are designed and the resulting temperature profiles are calculated. Finally, different cooling schemes are compared and the appropriate cooling advice is proposed.

Exploring fission and quasi-fission in $^{31}$Al + $^{197}$Au: Probing energies near and beyond Coulomb Barrier

Abstract An idea to understand the fragmentation of a formed nuclear entity (i.e. compound nucleus), induced via heavy-ion reactions, is an interesting task especially at incident energies near, above and far away from the Coulomb barrier. In the present work, we are studying the decay dynamics of a formed nuclear entity i.e. $^{228}$U$^*$ compound nucleus (CN), via the radioactive beam of Aluminium-31 ($^{31}$Al) striking on the stable Gold-197 ($^{197}$Au) target nucleus, for incident energies $E_{\textrm{\textrm{c.m.}}}$=106.2-163.2 MeV. A comprehensive knowledge regarding the probable decaying fragments from $^{228}$U$^*$ has been accumulated using the collective clusterization approach of the Dynamical Cluster-decay Model (DCM) in terms of mass and charge dispersion, which built up on the Quantum Mechanical Fragmentation Theory (QMFT). Through both of these dispersion cases, we have identified the decaying fragments in the fission and heavy-mass regions, at different scale of incident energies. Further, the fission cross-sections ($\sigma_{\textrm{fis}}^{\textrm{Theo}}$) have been obtained for $^{31}$Al+$^{197}$Au$\rightarrow^{228}$U$^*$ reaction at the above said $E_{\textrm{c.m.}}$ (MeV) and compared with the experimental data. This study has been carried out using two different sets of Skyrme force parameters (SIII and SSk), which are employed within the semiclassical approach of Skyrme Energy Density Formalism. Unlike for energies below and near the barrier, a significant difference has been observed between calculated ($\sigma_{\textrm{fis}}^{\textrm{Theo}}$) and experimental ($\sigma_{\textrm{fis}}^{\textrm{Expt}}$) cross-sections for above barrier energies, with independent choice of Skyrme forces. Such discrepancy noticed has been addressed with the presence of quasi-fission (\emph{QF}) event. Similar phenomena has also been seen for $^{19}$F-induced reaction forming the same CN ($^{228}$U$^*$), for excitation energy $E_{\textrm{CN}}^*>$ 42 MeV.

Basic properties of ferromagnetic vector hysteresis play models and their validation by finite element method

Purpose Magnetic hysteresis holds significant technical and physical importance in the design of electromagnetic components. Despite extensive research in this area, modeling magnetic hysteresis remains a challenging task that is yet to be fully resolved. The purpose of this paper is to study vector hysteresis play models for anisotropic ferromagnetic materials in a physical, thermodynamical approach. Design/methodology/approach In this work, hysteresis play models are implemented to interpret magnetic properties, drawing upon classical rate-independent plasticity principles derived from continuum mechanics theory. By conducting qualitative and quantitative verification and validation, various aspects of ferromagnetic vector hysteresis were thoroughly examined. By directly incorporating the hysteresis play models into the primal formulations using fixed point method, the proposed model is validated with measurements in a finite element (FE) environments. Findings The proposed vector hysteresis play model is verified with fundamental properties of hysteresis effects. Numerical analysis is performed in an FE environment. Measured data from a rotational single sheet tester (RSST) are validated to the simulated results. Originality/value The results of this work demonstrates that the essential properties of the hysteresis effects by electrical steel sheets can be represented by the proposed vector hysteresis play models. By incorporation of hysteresis play models into the weak formulations of the magnetostatic problem in the h-based magnetic scalar potential form, magnetic properties of electrical steel sheets can be locally analyzed and represented.

Cyclic R‐Curve Measurements for Structural Metallic Alloys

Fractures nucleated from defects and subjected to cyclic loading can experience propagation for a range of stress intensity factor ΔK well below the so‐called long crack threshold. This phenomenon is attributed to the development of crack closure mechanisms which may differ from those observed in laboratory tests conducted in accordance with current standards. Cracks originating from material defects require a specific degree of extension to develop the plastic wake, thus achieving a stabilized condition called the long crack threshold. However, in certain materials, this stabilization length can extend up to several millimeters, effectively encompassing a significant portion of the component's fatigue life. Therefore, understanding and quantifying the development of ΔKth with crack extension is important for implementing a reliable assessment procedure based on the fracture mechanics theory. Herein, R‐curve measurements are presented for five distinct structural metallic alloys widely used in various industrial applications. Additionally, the impact of load ratio is investigated, providing a comprehensive analysis of fatigue crack resistance in terms of the R‐curve concept. This study underscores the necessity of ruling new experimental techniques to measure and implement the long crack threshold, thereby ensuring the development of a reliable and robust framework for fatigue assessment.

Multi-condition simulation analysis of a sliding hydraulic support system based on elastoplastic mechanics

In response to the challenges of supporting fractured and weak surrounding rock in deep coal mines in the Huainan region of China, a self-moving hydraulic support system for roof support was designed and developed. This innovative solution addresses the difficulties encountered in providing continuous support to roof structures. Based on the theory of elastoplastic mechanics, a numerical analysis model was established to calculate the mechanical parameters such as the displacement, stress, and strain of hydraulic supports during the stepping process under multiple operating conditions. The results of the numerical simulation were compared and verified with those from an actual working site. The results show that the maximum equivalent stress is 245.33 MPa for operating condition 1, 246.82 MPa for operating condition 2, and 245.27 MPa for operating condition 3. The maximum stress values under the three working conditions do not exceed the yield strength of the material, satisfying the requirements for normal bracket support operations. These research findings can establish a theoretical framework for the comprehensive assessment of the reliability and stability of hydraulic supports and the optimization of construction processes.

Three-dimensional micro-force measurement method based on broadband optical coherence

In response to the high-precision and multi-dimensional force measurement requirements in the fields of biology and medicine, this paper proposes a novel three-dimensional microforce measurement method based on the broadband optical coherence. A novel, compact, and low-coupling elastic element was designed, with a maximum outer diameter of 26 mm and a capacity of 50 g in the X-, Y-, and Z-directions, respectively. The functional relationship between the displacements of the three detecting points on the elastic element and the applied external force was derived based on the elastic mechanics theory. And it was also verified by the finite element method. A self-built optics system was set up to sense the displacements of the three points on the elastic element. The experiments results showed that the resolution in the X-, Y-, and Z-directions was 0.10 mN, 0.11 mN and 0.13 mN, respectively. In the measuring range of (10–50) g, the maximum coupling rate was 4.55 %, and the maximum linear error was 4.70 %. The maximum repeatability error was only 0.615 %. The method and sensor were verified with good characteristics of high resolution, low coupling rate, high linearity and high accuracy, comparing to other reported researches. The multi-dimensional force measuring method could be used in the fields of biology and medicine.

Computational study on the endocrine-disrupting metabolic activation of Benzophenone-3 catalyzed by cytochrome P450 1A1: A QM/MM approach

Predicting the metabolic activation mechanism and potential hazardous metabolites of environmental endocrine-disruptors is a challenging and significant task in risk assessment. Here the metabolic activation mechanism of benzophenone-3 catalyzed by P450 1A1 was investigated by using Molecular Dynamics, Quantum Mechanics/Molecular Mechanics and Density Functional Theory approaches. Two elementary reactions involved in the metabolic activation of BP-3 with P450 1A1: electrophilic addition and hydrogen abstraction reactions were both discussed. Further conversion reactions of epoxidation products, ketone products and the formaldehyde formation reaction were investigated in the non-enzymatic environment based on previous experimental reports. Binding affinities analysis of benzophenone-3 and its metabolites to sex hormone binding globulin indirectly demonstrates that they all exhibit endocrine-disrupting property. Toxic analysis shows that the eco-toxicity and bioaccumulation values of the benzophenone-3 metabolites are much lower than those of benzophenone-3. However, the metabolites are found to have skin-sensitization effects. The present study provides a deep insight into the biotransformation process of benzophenone-3 catalyzed by P450 1A1 and alerts us to pay attention to the adverse effects of benzophenone-3 and its metabolites in human livers.

No-go theorem for static spherically symmetric configurations composed of two charged pressureless fluid species

We present a no-go theorem for spherically symmetric configurations of two charged fluid species in equilibrium. The fluid species are assumed to be dusts, that is, perfect fluids without pressure, and the equilibrium can be attained for a single dust from the balance of electrostatic repulsion and gravitational attraction. We show that this is impossible for two dust species unless both of them are indistinguishable in terms of their electric charge density to matter density ratio. The result is obtained in the main three theories of mechanics, that is, in Newtonian Mechanics, in Special Relativity and in General Relativity. In particular, as charged dust solutions have been used to study the possibility of black hole mimickers, this result shows that such mimickers can not be constructed unless the underlying charged particle has the correct charge to mass ratio.

Simulation study on hydraulic characteristics of Changzhou fishway based on FLUENT

Guangxi Changzhou Fishway is the first significant water conservancy project above the mouth of the Pearl River and also the first large fishway independently designed in China. It is the primary migration channel for six kinds of state-level protected fish, such as Chinese sturgeon and a typical vertical slit fishway. This paper takes the Changzhou fishway as the research object, based on the theory of fluid mechanics, and adopts the method of combining theoretical analysis, experimental research, and numerical simulation to study the flow field of different water depths in the pond. The analysis results show that the upper water flow has a larger resting area than the lower water flow, and the fishway has a rich flow field distribution and can produce “S” shaped meandering flow characteristics. The research results provide some reference for the design of vertical fishways.

Optimization design of plugging agent dosage and application of deep shale gas inner-diversion fracturing

China boasts abundant deep shale gas resources with considerable development potential. However, the weak brittleness and large horizontal stress contrast of deep shale rock may restrain the complex fractures network extension during hydraulic fracturing. To address this challenge, the inner-diversion fracturing technique is widely employed, facilitating the formation of a complex fractures network. Numerous theoretical studies emphasize the pivotal role of plugging pressure exerted by temporary plugging agents within fractures in enhancing deep shale stimulation performance. However, various types of temporary plugging agents with different plugging performances make it difficult to determine the optimal dosage of temporary plugging agents before fracturing operation. This study considered the dynamic propagation of fractures affected by the coupling of the induced stress from clustered fractures and the fluid pressure within the fractures into the mathematical model, based on rock mechanics theory. Subsequently, the inner-diversion capability testing instrument was utilized to evaluate the critical plugging pressure of several common temporary plugging materials. By integrating on-site data from temporary plugging and inner-diversion fracturing operations in the Southern Sichuan deep shale gas reservoir with this approach, the optimal dosage of temporary plugging agents in the operational scheme was refined. The fracturing operation curves demonstrate that the temporary plugging and inner-diversion pressure significantly increased after pumping the temporary plugging agent, indicating the hydraulic fractures successful plugging and a large-scale complex fractures network extension. This underscores the potential effectiveness of the temporary plugging dosage optimization method for inner-diversion fracturing. Furthermore, this study not only provides important guidance for optimal design but also mitigates the operational risks of inner-diversion fracturing in deep shale gas horizontal wells.

A Comprehensive Review of Indentation of Gels and Soft Biological Materials

Abstract Indentation measurement has emerged as a crucial technique for elucidating the mechanical properties of soft hydrated materials. These materials, encompassing gels, cells, and biological tissues, possess pivotal mechanical characteristics crucial for a myriad of applications across engineering and biological realms. From engineering endeavors to biological processes linked to both normal physiological activity and pathological conditions, understanding the mechanical behavior of soft hydrated materials is paramount. The indentation method is particularly suitable for accessing the mechanical properties of these materials as it offers the ability to conduct assessments in liquid environment across diverse length and time scales with minimal sample preparation. Nonetheless, understanding the physical principles underpinning indentation testing and the corresponding contact mechanics theories, making judicious choices regarding indentation testing methods and associated experimental parameters, and accurately interpreting the experimental results are challenging tasks. In this review, we delve into the methodology and applications of indentation in assessing the mechanical properties of soft hydrated materials, spanning elastic, viscoelastic, poroelastic, coupled viscoporoelastic, adhesion properties, and fracture toughness. Each category is accomplished by the theoretical models elucidating underlying physics, followed by ensuring discussions on experimental setup requirements. Furthermore, we consolidate recent advancements in indentation measurements for soft hydrated materials highlighting its multifaceted applications. Looking forward we offer insights into the future trajectory of the indentation method on soft hydrated materials and the potential applications. This comprehensive review aims to furnish readers with a profound understanding of indentation techniques and a pragmatic roadmap of characterizing the mechanical properties of soft hydrated materials.

From minimal strings towards Jackiw–Teitelboim gravity: on their resurgence, resonance, and black holes

Abstract Two remarkable facts about Jackiw–Teitelboim (JT) two-dimensional dilaton-gravity have been recently uncovered: this theory is dual to an ensemble of quantum mechanical theories; and such ensembles are described by a random matrix model which itself may be regarded as a special (large matter-central-charge) limit of minimal string theory. This work addresses this limit, putting it in its broader matrix-model context; comparing results between multicritical models and minimal strings (i.e. changing in-between multicritical and conformal backgrounds); and in both cases making the limit of large matter-central-charge precise (as such limit can also be defined for the multicritical series). These analyses are first done via spectral geometry, at both perturbative and nonperturbative levels, addressing the resurgent large-order growth of perturbation theory, alongside a calculation of nonperturbative instanton-actions and corresponding Stokes data. This calculation requires an algorithm to reach large-order, which is valid for arbitrary two-dimensional topological gravity. String equations—as derived from the Gel’fand–Dikii construction of the resolvent—are analyzed in both multicritical and minimal string theoretic contexts, and studied both perturbatively and nonperturbatively (always matching against the earlier spectral-geometry computations). The resulting solutions, as described by resurgent transseries, are shown to be resonant. The large matter-central-charge limit is addressed—in the string-equation context—and, in particular, the string equation for JT gravity is obtained to next derivative-orders, beyond the known genus-zero case (its possible exact-form is also discussed). Finally, a discussion of gravitational perturbations to Schwarzschild-like black hole solutions in these minimal-string models, regarded as deformations of JT gravity, is included—alongside a brief discussion of quasinormal modes.

Direct esterification of amides by the dimethylsulfate-mediated activation of amide C–N bonds

Amides are important intermediates in organic chemistry and the pharmaceutical industry, but their low reactivity requires catalysts and/or severe reaction conditions for esterification. Here, a novel approach was devised to convert amides into esters without the use of transition metals. The method effectively overcomes the inherent low reactivity of amides by employing dimethylsulfate-mediated reaction to activate the C-N bonds. To confirm the proposed reaction mechanism, control experiments and density functional theory (DFT) calculations were conducted. The method demonstrates a wide array of substrates, including amides with typical H/alkyl/aryl substitutions, N,N-disubstituted amides, amides derived from alkyl, aryl, or vinyl carboxylic acids, and even amino acid substrates with stereocentres. Furthermore, we have shown the effectiveness of dimethylsulfate in removing acyl protective groups in amino derivatives. This study presents a method that offers efficiency and cost-effectiveness in broadening the esterification capabilities of amides, thereby facilitating their increased utilization as synthetic compounds in diverse transformations.

Experimental and Numerical Studies on the Vibration of Hybrid Composite with an Edge Crack

The hybrid composite plate is increasingly used in marine, robotic arm, and other applications. Edge crack is the greatest common fault in the structural systems during its working time. In this research, the successful fabrications of a hybrid composite of epoxy-based composites reinforced with bamboo and glass fibers have been done to examine the vibration characteristics under free vibration. First-order shear deformation theory is used to study the fundamental natural frequencies of asymmetrically hybrid composite beam with edge cracks for cantilever beam boundary conditions. Both numerical (FEM) using ABAQUS software and experimental investigations are done for the vibration analysis of unidirectional bamboo/glass fiber epoxy hybrid composite (BGHC) beam with edge cracks using fracture mechanics theory. It is observed that implications edge crack with different crack depth and various fiber weight ratio parameters have a major effect on vibration analysis. Also, it is clear that the natural frequencies of the hybrid composite are significantly affected due to the fiber weight ratio and crack depth of the hybrid composite materials. So, crack lengths are playing a vital role in the dynamic or vibration characteristics of the hybrid composite materials. The results of natural frequencies have been shown that they are decreased with an increase in crack depth and an increase in the bamboo fiber weight. Thus, BGHC-2 made from 30% bamboo and 10% glass fiber can be a viable candidate for applications that will produce good vibration properties. Generally, the first-third natural frequency of the hybrid composite beam decreases within the increase of bamboo fiber and decreases in glass fiber. The composite materials having 60% of epoxy with 20% bamboo and 20% glass fiber, and 60% of epoxy with 10% glass and 30% bamboo fibers, are observed with a gradual decrease in the values of natural frequencies with respect to increasing in crack depth. A fine agreement was accomplished between the simulation and experimental results. Therefore, the present approach can be used to identify cracks for mechanical health monitoring by linking the variation in natural frequencies of the hybrid composite beams.

Experimental Study and Creep-Fatigue Life Prediction of Turbine Blade Material DZ125 Considering the Nonholding Effect and Coupling Effect of Stress and High Temperature

Abstract In response to the problem of creep-fatigue interaction damage failure of aero-engine turbine blade material, based on the modified damage evolution model of Kachanov-Rabotnov and Chaboche, a creep-fatigue life prediction model for nickel-based superalloy DZ125 is constructed considering the nonholding effect and coupling effect of stress and high temperature with the nonlinear interaction and superposition of creep damage and fatigue damage according to the continuum damage mechanics theory. Simultaneously, the microfracture morphology of DZ125 was analyzed using a scanning electron microscope, revealing the micromechanism of creep-fatigue interaction. The research results manifest that the creep-fatigue life prediction model has a high life prediction ability within ±2.0 times the dispersion band of the prediction results. Concurrently, a large number of intertwined tearing edges, microcracks, and microvoids appear in the fracture morphology, and creep and fatigue interact with each other in the form of effective stress. The above research can provide theoretical support for predicting the lifespan of mechanical structures in a high-temperature environment.

The whole-life ratcheting behavior of internal pressurized elbow subjected to force and displacement cycling with a damage-coupled kinematic hardening model

In this paper, a study was conducted on the ratcheting-fatigue tests of internal pressurized elbow in the primary circuit of nuclear power plant under force and displacement cycling, and the ratcheting effects at the critical locations of the elbow were evaluated. Based on thermodynamics and continuous damage mechanics theory, the damage evolution rule of the material was derived according to the derivative relationship between damage dissipation potential and damage related variable. A cyclic plastic constitutive model with damage was established by combining the damage evolution rule with Chen-Jiao-Kim (CJK) kinematic hardening rule. The subroutine of this constitutive model was embedded in ANSYS finite element software to numerically evaluate the evolution law of the whole-life ratcheting of the elbow. The results indicate that this damage-coupled kinematic hardening model can describe the whole-life ratcheting behavior of the elbow, and the numerical calculation results and experimental data are basically identical.

Recurrence of ventricular fibrillation in out-of-hospital cardiac arrest: Clinical evidence and underlying ionic mechanisms.

Defibrillation remains the optimal therapy for terminating ventricular fibrillation (VF) in out-of-hospital cardiac arrest (OHCA) patients, with reported shock success rates of ∼90%. A key persistent challenge, however, is the high rate of VF recurrence (∼50-80%) seen during post-shock cardiopulmonary resuscitation (CPR). Studies have shown that the incidence and time spent in recurrent VF are negatively associated with neurologically-intact survival. Recurrent VF also results in the administration of extra shocks at escalating energy levels, which can cause cardiac dysfunction. Unfortunately, the mechanisms underlying recurrent VF remain poorly understood. In particular, the role of chest-compressions (CC) administered during CPR in mediating recurrent VF remains controversial. In this review, we first summarize the available clinical evidence for refibrillation occurring during CPR in OHCA patients, including the postulated contribution of CC and non-CC related pathways. Next, we examine experimental studies highlighting how CC can re-induce VF via direct mechano-electric feedback. We postulate the ionic mechanisms involved by comparison with similar phenomena seen in commotio cordis. Subsequently, the hypothesized contribution of partial cardiac reperfusion (either as a result of CC or CC independent organized rhythm) in re-initiating VF in a globally ischaemic heart is examined. An overview of the proposed ionic mechanisms contributing to VF recurrence in OHCA during CPR from a cellular level to the whole heart is outlined. Possible therapeutic implications of the proposed mechanistic theories for VF recurrence in OHCA are briefly discussed.

Investigation on A Viscoelastic Creep Damage Constitutive Model for HTPB Propellant and Its Application in Finite Element Analysis

Solid rocket motor (SRM) is typically kept in storage for a significant portion of its lifespan. During storage, the propellant grain creeps under the action of gravity. To investigate the creep properties of hydroyl-terminated polybutadiene (HTPB) propellant under long-term loading, a creep damage constitutive model is developed based on the generalized Kelvin model and continuum damage mechanics theory. Parameters for this model are determined through creep tests conducted on HTPB propellant under various stress levels. Furthermore, to enable the application of the developed propellant constitutive model in the finite element analysis of SRM, the derived constitutive equation is transformed into an incremental form and integrated into the user subroutine UMAT of the finite element analysis platform ABAQUS. Subsequent to this, a three-dimensional SRM model containing the case, the insulator, and the propellant grain is established. The mechanical response of the grain under thermal and gravitational loads is calculated and analyzed. The results indicate that the stress concentration region in the grain is located at the stress release boot in the forward dome of the motor, where damage occurs. The methods employed in this paper and the conclusions drawn can serve as a reference for evaluating the structural integrity and storage lifespan of the SRM.

Effect of Post-Processing Heat Treatment on Micro-Contact Damage of Zirconia-Reinforced Lithium Silicate Dental Materials.

Zirconia-reinforced lithium silicate (ZLS) is utilized as a material for prosthetic tooth crowns, offering enhanced strength compared to other dental glass-ceramics. In this study, we investigate a commercial ZLS material, provided in a fully crystallized form. We examine the effects of an optional post-processing heat treatment on micro-contact damage using controlled indentation tests simulating the primary modes of contact during chewing: axial and sliding. Our findings indicate that the heat treatment does not affect mechanical properties such as the elastic modulus, hardness and indentation fracture toughness. However, it does enhance the resistance to contact damage by fracture and chipping in both axial and sliding modes, as well as the resistance to crack initiation measured from sliding tests. This improvement is attributed to the refinement of the flaw population achieved through the heat treatment. The results are analysed using principles of contact and fracture mechanics theory, discussing their significance in prosthetic dentistry.

Enhancing pore pressure prediction accuracy: A knowledge-driven approach with temporal fusion transformer

Pore pressure plays a crucial role in various fields, including geology, petroleum engineering, hydrology, and carbon capture, utilization, and storage (CCUS). Traditional pore pressure prediction methods, which rely on physical models, often fail to meet the required accuracy standards due to their inflexibility and technical parameterization. Although machine learning methods have been increasingly used for pore pressure prediction, they struggle to integrate domain-specific knowledge and capture the inherent temporal dynamics of the data, resulting in suboptimal prediction accuracy. To address these limitations, this study introduces the Knowledge-Aware TFT model, which determines the key parameter attributes for pore pressure prediction by comprehensively analyzing well logging data, rock mechanics theory, and pore pressure evolution theory. Additionally, the model effectively captures the temporal dynamic characteristics of the data, thereby enhancing the accuracy of pore pressure prediction. To validate the model's accuracy, uncertainty theory is employed to evaluate the experimental results, providing a description of the uncertainty associated with pore pressure prediction and supporting credibility assessment. A case study involving three vertical wells in Block X, China, compares the Knowledge-Aware TFT model with SVM, XGBoost, MLP, and LSTM models, further confirming its superior prediction accuracy (R^2 = 0.997, RMSE = 0.135) and demonstrating its practicality in pore pressure prediction. In conclusion, the proposed pore pressure prediction model not only improves prediction accuracy but also achieves excellent results in practical applications, making it a viable alternative to traditional technologies.