Deformation Problems Research Articles

Quality control of NiCr-Cr3C2-hBN@Ni coating on thin-walled GH4169 alloy surface prepared by plasma spraying

As equipment lightweight trends progress, thin-walled structures have seen extensive application in critical aerospace components. Nevertheless, the aero-engine tail nozzle flaps are exposed to the harsh operating conditions of high-temperature friction, so there is an urgent requirement to prepare wear-resistant, self-lubricating coatings with a wide range of temperatures for their protection. Due to the poor rigidity and weak strength of thin-walled workpieces and complex forms of structural stresses, the processing is extremely difficult. In order to solve the thermal deformation problem of coating workpieces prepared by spraying on the surface of thin-walled workpieces, the effects of spraying path, cooling airflow, and spraying interval on the thermal force field of thin-walled workpieces to prepare NiCr-Cr3C2-hBN@Ni coating are investigated in this study using finite element simulation. As a result, the deformation and stress of thin-walled workpieces can be minimized by adding back-side cooling air during the spraying process and moving the cooling air with the gun in a set interval, with the maximum warpage and maximum stress being less than 2.366 mm and 0.177 GPa, respectively. During the spraying process by simulating the optimum spraying process, no significant warpage of the substrate occurred and the coating was sprayed with uniform thickness. Typically, the thickness error rate is 16.7 %, and the coating hardness reaches 15–20 GPa, with excellent tribological properties in a wear rate of 10−5 mm3·N−1·m−1 and 10−6 mm3·N−1·m−1, which protects the workpiece effectively.

Analysis of the stress-strain state of the rotary device fastening part by the semi-analytical finite element method

The possibilities of the numerical apparatus developed on the basis of the semi-analytical finite element method are shown on the example of solving a specific problem. In the areas of maximum values, the parameters of the stress-strain state of the re-device fastening part were compared. It is worth noting the relatively complex configuration of the cross-section of the object, which led to a thorough study of the principles of constructing a grid area. The surface of interaction between the axis and the hull was modeled by a fairly thin layer of elements in relation to their thickness, which absorb only normal stresses. Analysis of the stress-strain state of the rotary device fastening part should be carried out from the standpoint of a spatial problem. Moreover, according to the results of the elastic calculation, the transition section between the body and the base plate turned out to be more loaded compared to the zone of contact interaction between the body and the axle. The data of the calculation performed in the elastic-plastic formulation made it possible to clarify the idea of the operating conditions of individual sections of the object and to draw a conclusion about the uniformity of the hull. The carried out studies confidently demonstrated the wide possibilities of the developed approach in solving new, practically important problems of elastic deformation of prismatic bodies of complex shape in the spatial formulation of new ones. To substantiate the reliability of the results of the calculation of the elements under consideration, a sequential increase in the number of FE in the cross-section and the number of retained terms of the decomposition along the length of the body, as well as an increase in the accuracy of solving systems of equations, are given. In addition, an assessment of the satisfaction of natural boundary conditions on the surface of the body and the conditions of equilibrium in the integral sense is given according to the characteristic sections within the region, which showed their fairly good performance. New data on the regularities of behavior of critical structures in the process of loading, due to the consideration of their physical and geometric parameters, have been obtained.

High-precision modelling of deformation of sandwich structures under bilateral symmetric and oblique-symmetric loading

The analysis and assessment of the stress-strain state (STS) of multilayer plates with orthotropic layers under the action of stationary transverse and tangential loads is an urgent task. It includes calculations on the strength and deformability of various homogeneous and multi-layered plates with layers of constant thickness but arbitrary structure according to the thickness of the plate. Combining materials with isotropic and transversely isotropic physical characteristics into a multilayer package allows you to create multifunctional structures. The SSS of such structures, due to their structural heterogeneity and relatively low transverse stiffness of the individual layers, is significantly associated with the influence of transverse shear deformations and transverse compression deformations. Therefore, the problem of refined modeling of SSS plates, which would take into account these types of deformations, is urgent. Based on the decomposition of the SSS plate into flexural and unflexural components, it is proposed to optimize the design scheme of deformation of a rectangular multilayer plate. This significantly simplifies its modeling. For unflexural and exclusively flexural SSS, a two-dimensional, high-degree iterative approximation, but three-dimensional models of deformation of multilayer rectangular plate on a rigid foundation with isotropic, transverse-isotropic and orthotropic layers are constructed in an elastic formulation. That models takes full account deformation of transverse shear and transverse compression at transverse and the tangential loading of a plate. The model is continuous, that is, the number of equations and the order of differentiation of the calculation system of equations does not depend on the number of layers in the slab. This order of differentiation and the number of calculation equations can depend only on the order of iterative approximation of the model. A way of precise satisfaction of all defining correlations of the layers of material under keeping the conditions of their contact is found, while in the known continual models the dependence between the cross normal stress and cross deformation is only integral.The results of the analytical solution of the problem of deformation of a rectangular plate under boundary conditions of the Navier type under the action of transverse and tangential loads are given. By solving the test problems of the deformation of two-layer plates with transversally isotropic layers and three-layer plates with orthotropic layers and comparing the solutions with the exact three-dimensional solutions of these problems obtained by known methods, an assessment of the accuracy of the proposed refined models is given. The limits of admissible parameters of elastic characteristics of transversely isotropic and orthotropic plates for application of the offered models are established.

Mechanical behavior of ECC-reinforced coupled shear wall

PurposeBased on the weak seismic performance and low ductility of coupled shear walls, engineered cementitious composites (ECC) is utilized to strengthen it to solve the deformation problem in tall buildings more effectively and study its mechanical properties more deeply.Design/methodology/approachThe properties of reinforced concrete coupled shear wall (RCCSW) and reinforced ECC coupled shear wall (RECSW) have been studied by numerical simulation, which is in good agreement with the experimental results. The reliability of the finite element model is verified. On this basis, a detailed parameter study is carried out, including the strength and reinforcement ratio of longitudinal rebar, the placement height of ECC in the wall limb and the position of ECC connecting beams. The study indexes include failure mode and the skeleton curve.FindingsThe results suggest that the bearing capacity of RECSW is significantly affected by the ratio of longitudinal rebar. When the ratio of longitudinal rebar increases from 0.47% to 3.35%, the bearing capacity of RECSW increases from 250 kN to 303 kN, an increase of 21%. The strength of longitudinal rebar has little influence on the bearing capacity of RECSW. When the strength of the longitudinal rebar increases, the bearing capacity of RECSW increases little. The failure mode of RECSW can be improved by lowering the casting height of the ECC beam in a certain range.Originality/valueIn this paper, ECC is used to strengthen the coupled shear wall, and the accuracy of the finite element model is verified from the failure mode and skeleton curve. On this basis, the casting height of the ECC casting wall limb, the strength and reinforcement ratio of longitudinal rebar and the position of the ECC beam are studied in detail.

Analysis of the Curing Deformation of Polyurethane Composite Solar Cell Bezels

In the present study, we investigated the deformation of polyurethane composite solar cell bezels during the curing process. To address the problem of deformation, thermochemical and curing kinetics models were developed to investigate the mechanical behavior of the resin during the curing process. The importance of the influencing factors was determined through orthogonal experiments and simulation analysis. The results showed that holding pressure had a significant effect on the amount of deformation of the bezel, followed by curing temperature, pultrusion speed, and holding time. The optimal combination of process parameters was a curing temperature of 150 °C, a pultrusion speed of 50 cm/min, a holding time of 12 s, and a holding pressure of 0.14 MPa, which aided in significantly reducing the deformation of the bezel and achieving effective control of curing deformation.

Modelling ductile damage in metals and alloys through Weyl condition exploiting local gauge symmetries

Local translational and scaling symmetries in space–time is exploited for modelling ductile damage in metals and alloys over wide ranges of strain rate and temperature. The invariant energy density corresponding to the ductile deformation is constructed through the gauge invariant curvature tensor by imposing the Weyl like condition. In contrast, the energetics of the plastic deformation is brought in through the gauge compensating field emerged due to local translation and attempted to explore the geometric interpretation of certain internal variables often used in classical viscoplasticity models. Invariance of the energy density under the local action of translation and scaling is preserved through minimally replaced space–time gauge covariant operators. Minimal replacement introduces two non-trivial gauge compensating fields pertaining to local translation and scaling. These are used to describe ductile damage, including plastic flow and micro-crack evolution in the material. A space–time pseudo-Riemannian metric is used to lay out the kinematics in a finite-deformation setting. Recognizing the available insights in classical theories of viscoplasticity, we also establish a correspondence of the gauge compensating field due to spatial translation with Kröner’s multiplicative decomposition of the deformation gradient. Thermodynamically consistent coupling between viscoplasticity and ductile damage is ensured through an appropriate degradation function. Non-ordinary state-based (NOSB) peridynamics (PD) discretization of the model is used for numerical implementation. We conduct simulations of uniaxial deformation to validate the model against available experimental evidence and to assess its predictive features. The model’s viability is tested in reproducing a few experimentally known facts, viz., strain rate locking in the stress–strain response, whose origin is traced to a nonlinear microscopic inertia term arising out of the space–time translation symmetry. Finally, we solved 2D and axisymmetric deformation problems for qualitatively validating the model’s viability. NOSB peridynamics axisymmetric formulation in finite deformation setup is also presented.

Mapped material point method for large deformation problems with sharp gradients and its application to soil‐structure interactions

AbstractThe material point method (MPM) is often applied to large deformation problems that involve sharp gradients in the solution field. Representative examples in geomechanics are interactions between soils and various “structures” such as foundations, penetrometers, and machines, where the displacement fields exhibit sharp gradients around the soil‐structure interfaces. Such sharp gradients should be captured properly in the MPM discretization to ensure that the numerical solution is sufficiently accurate. In the MPM literature, several types of locally refined discretizations have been developed and used for this purpose. However, these local refinement schemes are not only quite complicated but also restricted to certain types of basis functions or update schemes. In this work, we propose a new MPM formulation, called the mapped MPM, that can efficiently capture sharp gradients with a uniform background grid compatible with every standard MPM basis function and scheme. The mapped MPM is built on the method of auxiliary mapping that reparameterizes the given problem in a different domain whereby sharp gradients become much smoother. Because the reparameterized problem is free of undesirably sharp gradients, it can be well solved with the standard MPM ingredients including a uniform background grid. We verify and demonstrate the mapped MPM through several numerical examples, with particular attention to soil‐structure interaction problems.

Pressure-relief joints of initial support structural system used in tunnels with high-stress surrounding rock.

To address the problem of large deformations in weak surrounding rock tunnels under high ground stress, which cause damage to initial support structures, this study proposes a novel type of circumferential pressure-relief joint based on the concept of relieving deformation pressure of the surrounding rock. Key parameters of the pressure-relief joint, such as initial bearing capacity peak, constant bearing capacity, and allowable pressure-relief displacement, were obtained through numerical simulations and laboratory experiments. A comparison was made between the mechanical characteristics of rigid joints and the new type of pressure-relief joint. The applicability of the pressure-relief joint was verified through field tests, monitoring the surrounding rock pressure, internal forces in the steel frames, and the convergence displacement of the support structure. The results show that: (1) In the elastic stage, the stiffness of the new pressure-relief joint is similar to that of rigid joints. In the plastic stage, rigid joints fail directly, whereas the pressure-relief joint can control deformation and effectively release the deformation pressure of the surrounding rock while providing a constant bearing capacity. (2) The right arch foot in the experiment had poor rock quality, leading to high stress in the steel frame and significant horizontal displacement. After the deformation of the pressure-relief joint, the stress in the surrounding rock and steel frame significantly reduced, and the rate of horizontal deformation of the support structure slowed down. (3) The vertical and horizontal final displacements of the pressure-relief joint in the experiment were 61mm and 15mm, respectively, which did not exceed the allowable deformation values. The components of the support structure remained intact, ensuring safety. However, this study has limitations: the design of the new pressure-relief joint only allows for a vertical deformation of 150mm and a horizontal deformation of 50mm, limiting the range of pressure-relief deformation.

ПРОБЛЕМЫ ПРИМЕНЕНИЯ СОВРЕМЕННЫХ НОРМАТИВНЫХ ДОКУМЕНТОВ ДЛЯ РАСЧЕТА ТРАНСПОРТНЫХ СООРУЖЕНИЙ

About 400 normative documents were developed in the field of transportation construction, but the correctness and relevance of some of them is questionable. The lack of a unified terminology, the presence of contradictions and the increasing volume of documentation significantly complicate its use. In addition to general disadvantages, there are a number of private problems. For example, the authors point out the incorrect use of the limit states methodology for the calculation of structures, since this methodology considers limit (extreme) loads, and the regularities of the real behavior of the structure at lower levels of loads are unknown. In addition, the calculation according to limit states methodology does not take into account durability (it is not defined). When calculating using this methodology for the action of only loads with other unknown operating influences, the limit state is realized by reaching a certain limit value by this load. In reality, the limit state may occur due to changes in the shape of the structure, dimensions of cross-sections of structural elements and, more often, due to degradation of its material properties under the influence of service conditions. For the calculation of structures, it is necessary to apply the deformation approach more widely. According to it, both strength and deformation problems of structural calculation are correctly interrelated, and their hypotheses do not conflict with each other.

Study on the Influence of Mining Stress on the Sustainable Utilization of Floor Roadway in Qinan Coal Mine

Aiming at the problem of large deformations and difficult maintenance of cross-mining floor roadways, taking the track transportation roadway of the cross-mining east wing floor in Qinan Coal Mine as the engineering background, the stress field distribution of mining stress in floor strata and surrounding rock of floor roadway during the cross-mining process of the working face is studied by combining theoretical analysis with numerical simulation. The results show that the influence of mining stress on the vertical stress of floor strata is reflected in the stress-increasing area in front of the coal wall and the stress-decreasing area in the rear of the coal wall. With the increase in the depth of the floor strata, the peak value of the vertical stress gradually decreases, and the distance from the peak value of the vertical stress to the coal wall and the influence range of the vertical stress gradually increases. When the width of the coal pillar is greater than the influence range of advance abutment pressure of the working face, the development speed of the plastic zone is slow. When the roadway is located in the influence range of advance abutment pressure, the plastic zone of the roadway’s surrounding rock develops rapidly. When the working face crosses the floor roadway more than 10 m, the depth of the plastic zone of the surrounding rock of the roadway is no longer increased; the siltstone above the roadway is the key layer of fracturing, and the deformation of the roadway has been effectively improved after hydraulic fracturing. Through the analysis of numerical simulation results, the fracturing scheme has a significant effect on the stability control of the surrounding rock of the cross-mining floor roadway. This study has certain guiding significance for the maintenance and sustainable utilization of floor roadways in the cross-mining process, which is conducive to ensuring the sustainable mining of underground coal and the safety of personnel and equipment and is of great significance to the sustainable development of the coal mining industry.

Nonlinear Deformation of Cylinders from Materials with Different Behavior in Tension and Compression

A new numerical-analytical method for solving physically nonlinear deformation problems of axisymmetrically loaded cylinders made of materials with different behavior in tension and compression has been developed. To linearize the problem, the uninterrupted parameter continuation method was used. For the variational formulation of the linearized problem, a functional in the Lagrange form, defined on the kinematically possible displacement rates, is constructed. To find the main unknowns of the problem of physically nonlinear cylinder deformation, the Cauchy problem for the system of ordinary differential equations is formulated. The Cauchy problem was solved by the Runge-Kutta-Merson method with automatic step selection. The initial conditions were established by solving the problem of linear elastic deformation. The right-hand sides of the differential equations at fixed values of the load parameter corresponding to the Runge-Kutta-Merson’s scheme are found from the solution of the variational problem for the functional in the Lagrange form. Variational problems are solved using the Ritz method. The test problem for the nonlinear elastic deformation of a thin cylindrical shell is solved. Coincidence of the spatial solution with the shell solution was obtained. Physically nonlinear deformation of a thick-walled cylinder was studied. It is shown that failure to take into account the different behavior of the material under tension and compression leads to significant errors in the calculations of stress-strain state parameters.

The influence of geometrical shape on the buckling of thin-walled axisymmetric shells

The most economical for long span structures are thin-walled covering consisting of shell elements. These include shells of cylindrical, spherical, conical and other shapes. Buckling analysis of thinwalled structures is important in the design of buildings and structures. In this case, the geometric shape of the shell used has a great effect on the critical load. A comparative analysis of the geometrically nonlinear deformation, buckling, and postbuckling behavior of rotation panels of the same v olume under static thermomechanical loading is carried out. Spherical and conical shells having the same thickness, rise and weight are considered. Preheated shells are loaded with uniform external pressure. The calculation method is based on geometrically nonlinear relations of the three-dimensional theory of thermoelasticity without the use of simplifying hypotheses of shell theory and the use of a moment finite element scheme. A universal 3D isoparametric finite element is used. The element allows you to model shells of stepwise variable thickness, with breaks in the middle surface and with other geometric features in thickness. The problem of nonlinear deformation, buckling, and postbuckling behavior of inhomogeneous shells is solved by a combined algorithm that employs the parameter continuation method, a modified Newton–Kantorovich method, and a procedure for automatic correction of algorithm parameters. The method has been justified numerically in the authors' articles. Research has revealed the behavioral features of the compared shallow panels.

An explicit material point and finite volume sequentially coupled method for simulating large deformation problems in saturated soil

An explicit material point and finite volume sequentially coupled method (MPM-FVM) is developed using u-p form coupling formulations for the simulation of large deformations in saturated soil. In MPM-FVM, the momentum conservation equation is solved by MPM under the updated Lagrange framework, and the mass conservation equations are solved by FVM under the Euler framework. The numerical implementation of an explicit sequentially coupled algorithm is developed considering the tradeoffs between computational cost and numerical stability. The critical time step of u-p form governing equations is derived using the Von Neumann method, which is found to be much greater than the u-U form explicit MPM at low permeability, allowing for high numerical stability. Three numerical cases are presented to demonstrate the stability, efficiency, and effectiveness of the developed MPM-FVM method. The simulation of a saturated one-dimensional soil column subjected to quasi-static and dynamic loads validates the method, and highlights its greater efficiency and accuracy compared to standard solid–fluid coupled MPM methods. The large deformation simulation capability of the method is exhibited via simulation of a saturated slumping block. In real-world application, simulation results obtained using method achieves excellent agreement with the experiment measurements and observations of the Selborne landslide experiment.

Calculation and numerical modeling of the effect of heat and mass transfer on the properties of pile foundations in seasonally freezing soils

The phenomenon of heat and mass transfer in seasonally freezing soils has a significant impact on the condition of pile foundations. Building structures constructed in such soils experience extremely negative consequences: frost heave, vibration dynamics, moisture mass transfer and soil weakening during the thawing. Seasonally freezing soils occupy most of the territory of Kazakhstan, and in most regions the depth of soil freezing exceeds 1.5 m, there are settlements where the index reaches 1.97 m (Semiyarka, East Kazakhstan region) and in the north of the country - 2.74 m (Arshaly, Akmola region). Arrangement of foundation bases below the frost depth leads to increased construction costs, requires additional costs for thermal insulation, ventilation, other materials and structures, and, in addition, does not always lead to a full levelling of the negative impact of heat and mass transfer on the term and conditions of operation of buildings, structures, railways and roads. Therefore, the efforts of engineers and specialists in the field of thermal physics are aimed at finding effective ways to solve the problems of deformation and destruction of foundations in seasonally freezing soils. In the article an attempt is made to reveal the character of heat and mass transfer influence on pile foundations in seasonally freezing soils on the basis of a thermomechanical model.

Thermohyperelastic constitutive response for semilinear materials with application to deformation of a rotating thin disk

Constitutive modeling of soft elastomers is a well researched subject due to its numerous engineering applications. This study derives a thermodynamically consistent constitutive model for semilinear thermoelastic solids for which the strain energy density depends on the deformation gradient through the Biot stretch tensor. The Frechet derivatives, Coleman-Noll procedure, and product decomposition-based technique are employed to formulate the constitutive model. The combination of the derived model and thermomechanical field equations is specialized for application to problem of radial deformation of a rotating thin disk. The formulated model provides simple closed-form expressions for simulating thermomechanical responses of solids. Under suitable conditions, the derived three-configuration-based constitutive model reduces to the two-configuration-based constitutive equations. Finally, and among other things, the numerical solutions illustrate the effects of angular speed of rotation on thermal stress and displacement fields at points within the radially deforming rotating disk.

Prosthetic Rehabilitation of Post Covid Mucormycosis of Maxilla with Definitive Obturator Prosthesis- A 24 Month Follow Up Case Report

The second wave of COVID-19 in April 2021 witnessed a new mutated variant of SARS-CoV2 known as B.1.617 resulting in Mucormycosis. Inhalation, ingestion, or contamination of ulcerated mucosa by fungal spores results in infection and cause Mucormycosis. Objective: To highlight how a complex case of oral mucormycosis can be misdiagnosed due to its similar clinical presentations with other periodontal diseases and benefits of prosthetic rehabilitation of surgical defects with definitive obturator which improves the quality of life by restoring oral function and aesthetics. Case report: A 35-year-old female reported with chief complaint of pain, pus and mobility in upper front teeth region of 2 months and swelling of mid-face. Darkening of skin, swelling with tenderness over bilateral malar- infraorbital regions with epiphora and blurred vision in right eye and discharge from right nostril. She had multiple abscess in attached gingiva in incisor and premolar region of maxilla having probing depths ≤ 4mm with mobility. Conclusion: A precise diagnosis is prerequisite to specific treatment of any disease. Treatment often requires an extensive surgical resection causing facial deformation, masticatory, swallowing and speech problems. It is important to rehabilitate these patients by correcting the defects with the help of obturators and improve their lifestyle.

Stabilizing nodal integration in dynamic smoothed particle finite element method: A simple and efficient algorithm

The Smoothed Particle Finite Element Method (SPFEM) is a powerful numerical tool for the modelling of large deformation problems in the field of geomechanics. However, the standard SPFEM with nodal integration suffers from the rank deficiency problem due to under-integration. In this study, an hourglass-control based stabilization scheme is presented to overcome the rank deficiency in standard SPFEM with nodal integration. By introducing the hourglass-control based correction forces, the spurious low-energy models in standard SPFEM with nodal integration can be effectively suppressed. The presented stabilization scheme is simple and computationally efficient compared to the existing strain gradient-based stabilization approaches in SPFEM. The proposed hourglass-control based stabilized SPFEM is firstly validated by means of three benchmark examples and the results show that the stabilization scheme based on the hourglass-control can eliminate the rank deficiency instability in standard SPFEM and free of volumetric locking. Finally, two numerical examples related to the cohesive soil flow and the progressive failure of sensitive clay slopes are studied to highlight the robustness of the proposed stabilized SPFEM in solving large deformation geotechnical problems.

An ANS/ATFs‐based unsymmetric solid‐shell finite element algorithm for high‐quality finite deformation analysis of hyper‐elastic shell

AbstractAn effective updated Lagrangian (UL) algorithm is designed for extending the recent distortion‐tolerant unsymmetric 8‐node, 24‐DOF hexahedral solid‐shell element, US‐ATFHS8, to finite deformation analysis of hyper‐elastic shell structures. The distinguishing feature of this unsymmetric element is that two different interpolation schemes are employed for virtual displacement and real stress calculations, respectively. The assumed natural strain (ANS) method with shell assumptions, referring to the current configuration, is introduced to modify the strain tensors derived from the assumed virtual displacement fields in terms of isoparametric coordinates, thereby mitigating shear locking and trapezoidal locking. On the other hand, the analytical trial functions (ATFs) derived from the general solutions of homogenous governing equations for linear elasticity are updated in each increment step to obtain the incremental deformation gradient, which is then utilized for calculating the real stresses for curing the numerical difficulties in large deformation problems. Numerical examples show that the proposed algorithm enables the hyper‐elastic solid‐shell element US‐ATFHS8 to exhibit excellent performance in both regular and distorted meshes and yield considerable results even when other models cannot work.

Review of tunnels and tunnelling under unfavourable geological conditions

Considering the rapid expansion of the economy and the increasing demand for infrastructure development, the scale of the tunnelling is expanding, and tunnel is inevitably excavated under unfavourable geological conditions. Consequently, this brings multitude of risks and challenges to tunnels and tunnelling. This paper summarizes the engineering issues associated with five unfavourable geological conditions: soft soil strata, soft and hard composite strata, spatially variable strata, karst strata and subsea conditions. Various analysis methods for deformation problem of tunnel and tunnelling under these unfavourable geological conditions are discussed. The mechanisms of the progressive failure of tunnel faces and collapses of caves in karst tunnels are also presented, as well as the risk assessments and prevention strategies for karst tunnel and water inrush occurrences of subsea tunnel. Furthermore, the analysis of the response of subsea tunnels to dynamic loads such as wave forces and earthquakes is summarized. Additionally, the analysis and prevention techniques for constructing subsea tunnels in fault zones are also considered. Finally, this paper offers a glimpse into potential research directions for future analysis relevant to the topic discussed, aiming to provide guidance for secure construction and maintenance tunnels under unfavourable geological conditions.

Road surface crack detection based on improved YOLOv5s.

In response to the issues of low efficiency and high cost in traditional manual methods for road surface crack detection, an improved YOLOv5s (you only look once version 5 small) algorithm was proposed. Based on this improvement, a road surface crack object recognition model was established using YOLOv5s. First, based on the Res2Net (a new multi-scale backbone architecture) network, an improved multi-scale Res2-C3 (a new multi-scale backbone architecture of C3) module was suggested to enhance feature extraction performance. Second, the feature fusion network and backbone of YOLOv5 were merged with the GAM (global attention mechanism) attention mechanism, reducing information dispersion and enhancing the interaction of global dimensions features. We incorporated dynamic snake convolution into the feature fusion network section to enhance the model's ability to handle irregular shapes and deformation problems. Experimental results showed that the final revision of the model dramatically increased both the detection speed and the accuracy of road surface identification. The mean average precision (mAP) reached 93.9%, with an average precision improvement of 12.6% compared to the YOLOv5s model. The frames per second (FPS) value was 49.97. The difficulties of low accuracy and slow speed in road surface fracture identification were effectively addressed by the modified model, demonstrating that the enhanced model achieved relatively high accuracy while maintaining inference speed.