Subjects: Mechanics >> Basic Mechanics submitted time 2024-02-07 Cooperative journals: 《应用力学学报》
Abstract：
Ship wall climbing robots differ from land robots in that the former have both moving and adsorption functions,and can complete wall climbing motion on the inclined ship wall and complete the corresponding tasks by equipping high-pressure water guns,welding guns,image recognition and other devices required for rust removal,cleaning and welding.This paper introduces wall climbing robots and their wall climbing platforms designed and manufactured in recent years.Wall climbing platform design methods are classified into magnetic adsorption,negative pressure adsorption,and bionic type according to their adsorption principles and motion characteristics.The paper briefly introduces the mechanical structure design,motion performance,and application scope of various types of wall climbing platforms,in hope of providing inspirations for future design and manufacturing of marine robots and technology development.
Subjects: Mechanics >> Basic Mechanics submitted time 2024-02-07 Cooperative journals: 《应用力学学报》
Abstract： The fracture performance of concrete directly affects the safety and durability of the structure.The study on the law of crack propagation in concrete is the basis of analyzing the fracture performance of concrete.The fracture mechanism of concrete is very complicated and there are many influencing factors because concrete is heterogeneous,non-linear,polyphase,and has multiple initial cracks.At present,the fracture performance analysis method of ordinary cement concrete is relatively mature.According to its nonlinear characteristics,cohesive crack models and equivalent elastic fracture models have been established.Geopolymer is a kind of low-carbon and environmentally friendly building material with excellent mechanical properties,durability and high temperature resistance.Researchers carried out a study on the fracture properties of GPC based on the analytical methods of fracture mechanics of ordinary concrete.In this review,the development history of concrete fracture mechanics and the main factors affecting GPC properties are summarized.In addition,the factors affecting fracture properties of GPC are reviewed respectively,including raw material composition,alkali activators and fibers.Furthermore,the future work on the fracture properties of GPC is recommended.
Subjects: Mechanics >> Basic Mechanics submitted time 2024-01-03
Abstract： The proofs of the theorems of velocity and acceleration for synthetic motions of points in the existing textbooks are complicated, which bring more difficulties to classroom teaching and students’ learning. This paper proposes a new theorem proof method based on the rotation transformation matrix, in order to help students to grasp, understand and apply the velocity and acceleration synthesis theorem faster. This paper utilizes the theorem
of composition and the rotational transformation matrix methods to establish the analytical relationship equation of the absolute motion, transport motion and the relative motion of a particle. The theorem of composition of velocity for a point in plane motion, translation and rotation about the fixed axis are obtained by used the first order derivative of the analytic relationship equation with respect to time. Further, the acceleration synthesis theorem of particle in plane motion, translation and rotation about the fixed axis are obtained by used the second order derivative of the analytic relationship equation with respect to time. The proof process of this paper is mathematically simple and fluent, the physical concepts are clear and concise, and it is very suitable for teaching.
Peer Review Status:
Awaiting Review
Subjects: Mechanics >> Basic Mechanics submitted time 2023-11-09 Cooperative journals: 《应用力学学报》
Abstract：
Topological interlocking structures/materials is an emerging design concept.By the shape and size of the same blocks engaged with each other to form a structure with special properties,the elements are mutually constrained but not firmly bonded together,and which is called a topological interlocking structures/materials.Owing to its superior mechanical properties,such as outstanding toughness of structure,energy absorption capacity,resistance to local damage,and so on,it has received wider attention from more and more fields in recent years.Many researchers have carried out innovative studies on various aspects,so great research progress has been made in both theory and application.Its application covers many fields such as cushioning and damping,sound and energy absorption,and architectural design.This paper reviews the research progress and current status of topological interlocking structures/materials at home and abroad in recent years from the advantages,structure types and applications.Based on the analysis of the research status,this paper also looks forward to the future development trend and possible engineering applications of topological interlocking structures/materials.
Subjects: Mechanics >> Basic Mechanics submitted time 2023-11-09 Cooperative journals: 《应用力学学报》
Abstract： To develop and validate a 3D comprehensive finite element(FE)coupled model of the foot-shoe complex for revealing their biomechanical interaction and providing scientific basis for running shoe design optimization and related foot injury prevention.The collected CT images were used for establishment of the subject-specific coupled FE model.Boundary and loading conditions were quantitatively defined through 3D gait measurement.Both plantar and shoe sole regions were further divided for model verification.The Bland-Altman plot,Pearson correlation analysis,and T test were used for the reliability and effectiveness analyses between methods.Based on the established model,the effects of barefoot/shoed conditions and shoe sole stiffness on metatarsal stress were further studied.Results are as follows:1)The simulated peak pressure showed great consistency with the experimental data except for forefoot regions.Statistical analysis found that there was a significant correlation between the two methods(r=0.986; P<0.001),and that all the pressure difference points were scattered in the 95% limits of agreement,and the data had no significant difference(P=0.202),indicating a great agreement between the approaches.2)The stress was mainly distributed at the 2nd and 3rd metatarsal bones,with the 3rd one being the most stressed,and it increased in most metatarsal bones while barefoot standing compared to shoed condition.3)As the sole stiffness increased,the peak stress difference between the metatarsal bones increased,and the stress tended to concentrate on the 2nd and 3rd metatarsal bones.Conclusions are as follows:1)The insufficient simulated forefoot pressure may be related to its excessive longitudinal strain,and subsequent research should consider further optimization of the constraints.2)Barefoot and increased sole stiffness can lead to abnormal changes in metatarsal stress; thus in terms of running shoe design,it is suggested to consider adding a buffer structure at the metatarsal region for optimizing the metatarsal stress distribution and further reducing any potential injury risk.
Subjects: Mechanics >> Basic Mechanics submitted time 2023-11-09 Cooperative journals: 《应用力学学报》
Abstract： Wormlike micellar fluids formed by dissolving surfactants in water have unique mechanical responsesdue to its high surfactivity and strong viscoelasticity.These properties enable wormlike micellar fluids rich and complicated flow behaviors.By considering the breakage of long chains and the reforming of short chains,a two species VCM model is introduced in this study to numerically investigate the effect of the chain scission on the flow instability.First,the rheological properties are obtained by directly solving the VCM constitutive equation set numerically.The fluid exhibits a strong nonlinear thickening-thinning-thickening phenomenon under the uniaxial tension.The flow passing by a confined cylinder is investigated.The flow becomes significantly unstable at very low Reynolds numbers(Re～0.01)when the Weissenberg number is larger than 1.The fluid velocity in the downstream wake of the cylinder presents a fluctuation with the time.The flow fluctuation is quasi-periodic according to the power spectrum analysis.The flow fluctuation becomes more irregular when the nonlinearity of the variation of the tension stress with the elasticity becomes stronger.A pair of symmetrical vortexes behind the cylinder changing with time are also observed,indicating that the elasticity promotes the flow separation on the cylinder surface.The flow instability is due to the strong nonlinear response of the tension stress within the bulk fluid to the elasticity of the fluid.
Subjects: Mechanics >> Basic Mechanics submitted time 2023-11-09 Cooperative journals: 《应用力学学报》
Abstract： The three dimensional bar element was used to simulate the structural members.A single element model suitable for creep analysis of CFST spatial truss arch was established and the program was developed based on the characteristics of strain compatibility resulted from the good bond between steel tube and core concrete,and the time step incremental analysis method of creep was accommodated.The comparative analysis about the deflection of the arch rib,the section stress and the redistribution of the internal force of the member were carried out for the Maocaojie Bridge in Hunan Province(CFST arch with a main span of 368 m),in which the two creep modes specified in code for design of highway concrete filled steel tubular arch bridges(JTG-TD65-2015)and code for design of highway reinforced concrete and prestressed concrete bridges and culverts(JTG D62-2004)were used.The results show that the single element model for CFST member studied in this paper can improve the calculation efficiency compared with the conventional dual elements model.The deflection change of arch rib and the redistribution of section stress for steel tube and core concrete caused by creep are very obvious,and the redistribution of internal force of members is not obvious under the two creep modes,while the influence of creep on the behavior of arch rib is stronger under the latter creep mode.
Subjects: Mechanics >> Basic Mechanics submitted time 2023-11-09 Cooperative journals: 《应用力学学报》
Abstract：
Focusing on the creep behavior of concrete,the fractional-order model simulation and the corresponding multi-parameter identification are studied and analyzed in this paper.Both the modified fractional Maxwell model and the fractional Poynting-Thomson model are proposed to simulate experimental data of concrete creep.The results are compared,and the validity of the two models is verified by data fitting and error analysis.As for the corresponding multi-parameter identification,both the Bayesian algorithm and the cuckoo search algorithm are used to identify the multiple parameters in the two models.Results show that the modified fractional Maxwell model and fractional Poynting-Thomson model are both effective in describing the creep characteristics of concrete.Both the Bayesian algorithm and the cuckoo search algorithm are feasible in the fractional multi-parameter estimation problem,but the cuckoo algorithm has higher search speed,smaller error,higher efficiency,and better performance in the multi-parameter identification problem of the fractional order model.
Subjects: Mechanics >> Basic Mechanics submitted time 2023-11-09 Cooperative journals: 《应用力学学报》
Abstract： A three-dimensional crackable continuous-discontinuous method mainly suitable for cube elements is proposed to simulate deformation and tensile cracking processes of rocks.Its essence is a hybrid method of the three-dimensional Lagrangian element method and the fictitious crack model in fracture mechanics.Introduction of the fictitious crack model into the three-dimensional Lagrangian element method consists of three key steps.First,the nodal stress is obtained by averaging stresses of elements around the node,and the nodal separation is assessed according to the maximum principal stress of the node and the uniaxial tensile strength.Then,the element boundary closest to the plane perpendicular to the maximum principal stress of the node is selected.Finally,the fictitious fracture model is introduced to simulate the processes of crack initiation and propagation.Deformation and tensile cracking processes of specimens in uniaxial tension and three-point bending are simulated by using the present method.The effects of I-type fracture energy,rock specimen height and elements size on the direct tension processes are analyzed.Meanwhile,through comparing the present results with the theoretical peak stress and critical displacement of the specimen in direct tension and the numerical load-displacement curve of the specimen in three-point bending,the correctness of the proposed method is verified,laying a good foundation for future work.
Subjects: Mechanics >> Basic Mechanics submitted time 2023-11-09 Cooperative journals: 《应用力学学报》
Abstract： The method of combining theoretical analysis and numerical simulation is used to study the deformation law and energy absorption performance of multi-layer gradient sandwich panels under out-of-plane compressive loading.Based on the theory of super-folded elements,a theoretical analysis model of the mean compressive force(MCF)of single-layer,double-layer and three-layer trapezoidal sandwich panels was established.On this basis,a finite element model of the multilayer trapezoidal sandwich panel was established,and the influence of the thickness of the panel,the thickness of the core layer and the bottom angle of the core layer on the mechanical properties of the three-layer trapezoidal sandwich panel was studied.The research results show that the theoretical prediction is in good agreement with the numerical simulation results; the thickness of the panel in the three-layer trapezoidal sandwich panel has less influence on the specific energy absorption of the structure,and the thickness and bottom angle of the core layer have a greater influence.The panel thickness increases from 0.5 mm to 1.0 mm,the specific energy absorption increases from 10.93 J/g to 10.98 J/g,and when the panel thickness becomes 1.5 mm,the specific energy absorption decreases to 7.54 J/g.As the core layer thickness and bottom angle increase,the specific energy absorption of the structure increases.When the core layer thickness increases from 0.5 mm to 1.5 mm,the specific energy absorption becomes 4.69 times the original; when the core layer bottom angle is 63°.The energy absorption of the structure is 4.29 times that of the base angle of 30°.
Subjects: Mechanics >> Basic Mechanics submitted time 2023-11-09 Cooperative journals: 《应用力学学报》
Abstract：
The average orientation coefficient of steel fiber is an important factor to characterize the influence of fiber comprehensive orientation on concrete performance.In order to explore the influence of average orientation coefficient of steel fiber on the damage and cracking of steel fiber reinforced concrete composites in microscopic level,in this paper,a two-dimensional finite element model of steel fiber reinforced concrete composed of steel fiber,cement mortar and interface transition zone of three-phase materials was established based on the parametric language,and the whole process of uniaxial tensile failure of steel fiber reinforced concrete under different average orientation coefficient was simulated.Results show that the tensile strength of concrete increase with the average orientation coefficient; the crack resistance and toughening effect of steel fiber on concrete is also enhanced,which further reveals the damage mechanism of steel fiber reinforced concrete under uniaxial tension.
Subjects: Mechanics >> Basic Mechanics submitted time 2023-11-09 Cooperative journals: 《应用力学学报》
Abstract：
It is difficult to carry out laboratory and field mechanical tests on engineering-scale dissolution rock mass,which leads to great difficulty in obtaining mechanical parameters of the dissolution rock mass.Therefore,based on the characteristics of rock mineral content,laboratory mechanical tests,and rock mass structural plane characteristics,three-dimensional particle flow of discrete element method was adopted to conduct a uniaxial compression numerical test by establishing an equivalent dissolution rock mass model.Finally,the mechanical properties and deformation failure mechanism are analyzed.Based on the characteristics of meso-minerals and macro-structural planes,the research shows that the establishment of an equivalent dissolution rock mass model can truly reflect the mechanical behavior of it.In the early stage of loading,the structural plane of rock mass was quickly destroyed to produce micro-cracks mainly of shear.However,with the loading progressing,tensile failure occurred gradually in the rock mass,and its micro-cracks increased exponentially,while the micro-cracks of the structural plane surged first and then stabilized.Under the same axial strain,the internal tensile cracks in the rock block increase by the dissolution rate,but the shear microcracks on the structural plane decrease.The deformation and failure of the rock mass can be divided into four stages:rapid failure of the structural plane,elastic deformation of the rock,plastic deformation of the rock,and complete failure of the rock mass.The failure form of the rock mass transitions from the overall-uniform failure to the local-structural failure with the increase of the dissolution rate.dissolution reduces the strength of rock mass.The dissolution rate is inversely proportional to the uniaxial compressive strength,and has a negative exponential relationship with the deformation modulus.
Subjects: Mechanics >> Basic Mechanics submitted time 2023-11-09 Cooperative journals: 《应用力学学报》
Abstract： To study the fatigue crack growth rate(FCGR)of X56 pipe-in-pipe submarine pipeline steel after service,the fatigue crack growth tests under different maximum fatigue loads(Pmax=9 kN,10 kN,12 kN)were carried out on standard compact tensile(CT)specimens taken from the outer pipe of pipe-in-pipe in air and seawater,respectively.Compared with the fatigue crack growth rates of the CT specimens in air,when the crack grows to 15.38 mm,the fatigue crack growth rates of the CT specimens in seawater under the load of 9 kN,10 kN and 12 kN are increased by 1.82 times,1.54 times and 1.43 times,respectively.As the crack growth length increases,fatigue load plays a leading role,and the influence of seawater decreases gradually.A comprehensive analysis of the influence of the maximum fatigue load on fatigue crack growth is conducted.It is found that under the premise of the same crack length,the fatigue load increases,the stress intensity factor amplitude(ΔK)and the fatigue crack growth rate(da/dN)increase,and the influence of seawater corrosion gradually decreases.The maximum fatigue load applied in the fatigue crack growth test has a more significant impact on the fatigue life of the CT specimens,but has a negligible effect on the Paris constant.The fatigue fracture faces of different CT specimens observed by scanning electron microscope are all transcrystalline fractures.The fatigue fracture faces of CT specimens in seawater show more secondary cracks and higher tear ridges.With the increase of the maximum load,the crystal face area and the height difference of the cleavage steps formed by cleavage fracture gradually increase,and the rougher the fatigue fracture,the more pronounced the cleavage characteristics.
Subjects: Mechanics >> Basic Mechanics submitted time 2023-11-09 Cooperative journals: 《应用力学学报》
Abstract： In order to explore the flexural performance of grouted micro steel pipe piles,12 specimens with different steel pipe diameters,wall thicknesses and mortar strengths were subjected to pure bending tests using orthogonal test schemes,and the ultimate flexural bearing capacity expression was proposed based on the test results.Formula,and use the finite element software ANSYS to establish a model for verification.The results show that the whole bending process of grouting micro steel pipe pile can be divided into three stages,namely:elastic stage,elastoplastic stage and strengthening stage; the sensitivity to the ultimate load of grouting micro steel pipe is steel pipe diameter > steel pipe wall thickness >mortar strength grade; the ultimate flexural bearing capacity calculated by different regulations is quite different from the test.The expression of the ultimate flexural bearing capacity of the grouted micro steel pipe pile proposed in this paper is in good agreement with the test results.The flexural bearing capacity of the steel pipe It accounts for about 78% of the total flexural bearing capacity of the grouted micro steel pipe piles,and the mortar in the pipe accounts for about 22%.The finite element simulation results show that the mortar in the pipe greatly improves the flexural performance of the micro steel pipe piles.The correctness of the expression of the flexural bearing capacity of the grouted micro-steel piles proposed is recommended to be promoted.
Subjects: Mechanics >> Basic Mechanics submitted time 2023-11-09 Cooperative journals: 《应用力学学报》
Abstract： In order to investigate the interfacial bond behavior between cold-formed thin-walled steel and fiber reinforced lightweight aggregate concrete and the feasibility of using magnesium phosphate cement(MPC)as interfacial binder,it provides a reference for the future research on enhancing the interfacial bonding strength of composite structure.Through the push-out tests of 8 groups of specimens,the failure phenomenon,load-slip curve,interfacial bond energy index and interfacial damage were analyzed.The test results show that the cracking load,peak load and residual bearing capacity of the specimen will increase with the addition of fiber; after the bond interface is smeared with MPC,the bond bearing capacity will be further increased,and the yield platform corresponding to the load-slip curve becomes more obvious.The application of MPC has a greater effect on the bond energy index of the specimen than that of fiber,in which the increase of elastic deformation energy is more obvious,which greatly delays the speed of the specimen reaching the failure state,and restrains the damage development of the whole loading process.The application of MPC in LC30 lightweight aggregate concrete and steel fiber lightweight aggregate concrete will achieve better results.
Subjects: Mechanics >> Basic Mechanics submitted time 2023-11-09 Cooperative journals: 《应用力学学报》
Abstract： There are multiple cracks of different sizes in rock mass,forming cracked rock masses of different structural forms.The existence of cracks not only reduces the mechanical properties of rock mass,but also significantly affects the overall stability of rock mass engineering.Based on the sliding wing crack model,this paper theoretically deduces and analyzes the creep deformation of rock mass with single fracture under constant load.Based on the MAPLE software,the impact of the crack angle and length on the creep deformation under constant load is intuitively given.Apart from that,continuous-discontinuous numerical analysis software GDEM is used to numerically simulate the creep rupture crack propagation of rock mass under different inclination angles and different lengths of prefabricated single fissures.By theoretical analysis and numerical simulation,it can be observed that the creep rate of rock mass increases with the increase of crack length.Moreover,with the increase of crack angle,the creep rate first increases and then decreases,and it is the largest when the crack inclination angle is 30°.In short,the study on creep rupture crack propagation law of rock mass with single fissure can provide certain theoretical basis and reference for research on creep rupture law and creep control of rock mass engineering.
Subjects: Mechanics >> Basic Mechanics submitted time 2023-11-09 Cooperative journals: 《应用力学学报》
Abstract： The calculation of tunnel support structure is often assumed to be positive circular,but it is different from the actual engineering.Based on the theory of surrounding rock pressure calculation,this paper improves the calculation model of support structure of Japanese Yamamoto method,and puts forward a calculation model of three-center circular support structure of shallow buried tunnel in mountain.The results of the improved method are compared with those of the method,the code of tunnel design and the measured values.The results show that the surrounding rock pressure and axial force of supporting structure are the closest to the measured data,the maximum error is 12.9%,tend to be safe.According to the calculation results,the load concentration is determined and the special reinforcement scheme is made to ensure the safety of tunnel construction and operation.The research results can provide a reference for optimizing the theory of circular tunnel section and a new method for calculating tunnel support structure.
Subjects: Mechanics >> Basic Mechanics submitted time 2023-11-09 Cooperative journals: 《应用力学学报》
Abstract：
Conductor galloping has long been an important factor affecting the winter safety of transmission lines.Based on Fluent and ABAQUS,the aerodynamic coefficients of eight-bundle conductor with crescent-shaped iced are obtained to analyze the galloping stability.The conductor lines with different strain insulator strings are taken as the object to study the torsional stiffness and dynamic characteristics,and analyze the galloping characteristics like amplitude,time history of displacement and motion traces of conductors under different strain insulator string connection forms,wind speeds and initial attack angles.The results show that compared with single string,multiple strain insulator strings increase the torsional stiffness of eight split conductor lines,and change the low-order natural frequency obviously,which makes the vertical and torsional vibration coupled not easily; multiple strain insulator strings obviously change the galloping shape and increase the vertical galloping amplitude,which are great impacts on the galloping characteristics of conductor lines; the higher wind speed is,the higher galloping amplitude is; at the different initial wind attack angle,the galloping characteristics of conductor lines change obviously,which is consistent with the calculation range of galloping stability.The results provide guidance for the analysis of galloping characteristics of conductor lines and the research of anti-galloping technology.
Subjects: Mechanics >> Basic Mechanics submitted time 2023-11-09 Cooperative journals: 《应用力学学报》
Abstract：
Conductor galloping has long been an important factor affecting the winter safety of transmission lines.Based on Fluent and ABAQUS,the aerodynamic coefficients of eight-bundle conductor with crescent-shaped iced are obtained to analyze the galloping stability.The conductor lines with different strain insulator strings are taken as the object to study the torsional stiffness and dynamic characteristics,and analyze the galloping characteristics like amplitude,time history of displacement and motion traces of conductors under different strain insulator string connection forms,wind speeds and initial attack angles.The results show that compared with single string,multiple strain insulator strings increase the torsional stiffness of eight split conductor lines,and change the low-order natural frequency obviously,which makes the vertical and torsional vibration coupled not easily; multiple strain insulator strings obviously change the galloping shape and increase the vertical galloping amplitude,which are great impacts on the galloping characteristics of conductor lines; the higher wind speed is,the higher galloping amplitude is; at the different initial wind attack angle,the galloping characteristics of conductor lines change obviously,which is consistent with the calculation range of galloping stability.The results provide guidance for the analysis of galloping characteristics of conductor lines and the research of anti-galloping technology.
Subjects: Mechanics >> Basic Mechanics submitted time 2023-11-09 Cooperative journals: 《应用力学学报》
Abstract：
In order to improve the ductility performance of railway gravity piers,the design method of local unbonded reinforcement at the bottom of piers is proposed.Five piers with different types of unbonded steel bars are designed.Numerical analysis is used to study the influence of the amount and height of unbonded reinforcement on the seismic performance of railway gravity piers.It is found that the unbonded reinforcement at the bottom of the pier can effectively improve the ductility performance of the railway gravity pier,and it has little influence on the bearing capacity and stiffness of the pier,but it will increase the “pin-ching” effect of the shape of the hysteresis curve of the pier.The ductility performance of piers gets better with the increase of the amount of unbonded reinforcement.The unbonded height of reinforcement has a great influence on the ductility of pier in a certain range.The feasibility of improving ductile seismic performance by installing unbonded reinforcement at the bottom of pier is verified by numerical analysis.The research results can be applied in the research field of seismic design of railway gravity piers.
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