Mechanical simulation method for ice-pavement interlayer contact of ice suppression material

Abstract

The invention discloses a mechanical simulation method for ice-pavement interlayer contact of an ice suppression material, and relates to the technical field of road engineering. ABAQUS software is used for establishing a two-dimensional expansion finite element model of an ice-pavement combined structure; the model parameters comprise a hypothesis foundation, an initial external force, a model structure, a grid type, a grid density, a material attribute, a displacement boundary condition and a contact type; the numerical influence on the icing strength under the conditions of pavement macroscopic texture (aggregate exposure height and aggregate gaps), ice forming process (ice layer thickness and environment temperature) and the like is analyzed, the optimal icing strength value is determined, and the ice suppression efficiency is improved.

Description

Technical Field

[0001] The invention relates to the technical field of road engineering, and in particular to a mechanical simulation method for contact between ice-road surface layers and an ice-suppressing material. Background Art

[0002] In autumn and winter, snowfall usually occurs in the form of 0-4℃ ice-water paste at the beginning. Once the temperature drops sharply at night, it immediately turns into a hard ice body. Ice on the road surface will greatly weaken the road's anti-skid ability. Relevant studies have shown that the friction coefficient of dry asphalt pavement during driving and braking is 0.6, the friction coefficient of snowy asphalt pavement drops to 0.28, and the friction coefficient of icy asphalt pavement drops to 0.18, which are 68% and 76% lower than dry asphalt pavement, respectively. If these unfavorable factors happen to occur in special terrains such as bridges, tunnels, long downhills, and curves, the disadvantages will be greatly magnified, threatening people's personal and property safety. The transportation department shows that about 30% of traffic accidents are related to road icing. Traditional passive deicing technology has hysteresis, and active deicing technology is mostly used for newly built roads. Salt loss cannot be replenished and the cost is high. Spray the deicing material on the road surface before the arrival of low temperatures. Under the action of driving load, the deicing agent is released to directly melt thin ice or reduce the adhesion between ice and road surface, which is convenient for mechanical removal.

[0003] Ice bonding strength is affected by mechanical bite force, chemical bond force, and intermolecular force. The difference is that the proportion of each factor in different ice bonding systems is different, and the strength of the action is different. In the freezing of ice-road surface, because the asphalt surface is rough and has a certain structural depth, the mechanical force has a greater influence. In addition, the formation process of ice is also an important part affecting strength. The lattice and strength of ice materials vary greatly at different temperatures. At lower temperatures, the lattice is stronger. From the microscopic structure of ice, when the water temperature is lower than 0℃, this state of water is called supercooled water. The freezing process is divided into three stages: nucleation-nucleus growth-freezing. Temperature change is an important factor affecting the transformation of ice nuclei. It is generally believed that the thickness of the ice layer is proportional to the ice bonding strength. The thicker the ice layer, the greater the ice bonding strength. The freezing of the ice layer is in the order of internal freezing first and external freezing later. The ice molecules that freeze first have a long binding time, are close to each other, are close to each other, and have strong intermolecular forces. The ice molecules that freeze later have a short binding time, are far away, and have weak intermolecular forces.

[0004] Finite element analysis can be divided into three steps: pre-processing, calculation, and post-processing. Pre-processing is to establish a model, define materials, define constraints, and divide the mesh. Post-processing is to submit the job, output the results, provide animation, cloud map, and the results at a certain node. The following steps are generally used to solve the problem: (1) Determine the problem and the solution domain. Determine the geometric size and physical properties of the solution domain based on the actual object being simulated. (2) Discretize the continuous solution domain. Generally speaking, the solution domain is composed of a finite number of discrete domains of different shapes and sizes but connected to each other. The discretization process is called meshing. The smaller the unit, the greater the similarity of the discrete domain, the finer the calculation accuracy, but the amount of calculation increases accordingly. (3) Determine the boundary conditions and control methods. Converting the actual problem into a differential equation with different material parameters, state variables, and boundary conditions is the basis of finite element software. The differential equation is expressed in an equivalent functional form. (4) Establish the unit stiffness matrix. Construct an approximate solution for the unit, give the discrete relationship of each state variable by a specific method, and establish the unit stiffness matrix. (5) General assembly solution. According to the principle of static equivalence, the total stiffness matrix of the discrete domain is formed so that the continuity meets the specified conditions. (6) Establishment and solution of the equilibrium equations. The simultaneous equations can obtain the results of the state variables at the unit nodes. The finite element method is mostly implemented using Abaqus software. Abaqus software can solve simple linear analysis and can also simulate nonlinear problems. It contains a rich data unit library (which can simulate any geometric shape).

[0005] Due to the fast calculation and analysis speed of ABAQUS software and its certain reliability in processing complex systems, it is widely used in the field of engineering design. In recent years, ABAQUS software has been successfully used in asphalt concrete research. The simulation of the mechanics of ice suppression materials in contact between ice and pavement layers can accurately judge the changes in the structure between ice and pavement layers, improve the ice suppression efficiency to a certain extent, and can also be used in various forms and methods of ice suppression pavement research. Summary of the invention

[0006] The technical problem to be solved by the present invention is to provide a mechanical simulation method for the contact between ice-road surface and ice-road surface, to make an accurate judgment on the structural changes between ice-road surface and ice-road surface, to determine the optimal icing strength parameter value, and to improve the ice suppression efficiency.

[0007] The technical problem to be solved by the present invention is achieved by adopting the following technical solutions:

[0008] A mechanical simulation method for the contact between ice-pavement and anti-icing materials is proposed. A two-dimensional extended finite element model of the ice-pavement composite structure is established using ABAQUS software. The model parameters include assumed basis, initial external force, model structure, mesh type, mesh density, material properties, displacement boundary conditions and contact type. The numerical influence of pavement macro texture (aggregate exposure height, aggregate gap) and ice formation process (ice layer thickness, ambient temperature) on icing strength is analyzed to determine the optimal icing strength value and improve ice suppression efficiency.

[0009] In order to facilitate the calculation and analysis of the mechanical response of road ice suppression, the assumptions are as follows:

[0010] ① Asphalt mortar, aggregate and ice layer are all continuous, isotropic linear elastic materials. The stress and deformation are all within the elastic range. Their elastic parameters are characterized by elastic modulus E and Poisson's ratio μ, and their mechanical properties obey Hooke's law.

[0011] Hooke's law states that when an object is subjected to an external force and the stress is not greater than the yield stress σ0, the stress σ1 and the strain ε1 are in a positive linear relationship.

[0012] σ1=Eε1

[0013] Wherein, E is the elastic modulus (or Young's modulus).

[0014] ②The fixed contact between aggregate and asphalt mortar is completely continuous.

[0015] ③ The ice surface and the road surface will not invade each other when in contact, and the layers will maintain contact without gaps.

[0016] ④ Ignore minor factors such as the vehicle's lateral force and impact force, and focus on vertical loads and horizontal loads.

[0017] The initial external force is divided into vertical load and horizontal load. The vertical load acts on the road surface according to the standard single-axle double-wheel uniform load, and the direction is vertically downward; the horizontal load is determined by the friction coefficient of the road surface when icy, and the horizontal pressure is obtained according to the formula q=fp.

[0018] The model structure is a layered structure, which includes a thin ice layer and an asphalt surface layer from top to bottom.

[0019] The mesh type is an eight-node quadratic plane strain reduced integration element.

[0020] The grid density is determined by the contact position between the aggregate, the ice layer and the asphalt surface, and is freely divided by a non-homogeneous grid, with a denser division at the aggregate and a gradually sparser division at other positions.

[0021] The model material properties are aggregate parameters, asphalt mixture and ice layer parameters.

[0022] The displacement boundary conditions are that there is no displacement in the X and Y directions at the bottom of the model and it is fully constrained; there is no displacement in the X direction on both sides of the model and it is fully constrained.

[0023] The contact type adopts a penalty friction formula that allows relative sliding (called elastic sliding) between surfaces in the "bonded" state to simulate the contact surface, ensuring that the displacement and vertical stress on the contact surface can be continuously transmitted. Coulomb friction is used to simulate the tangential action between the contact surfaces, and the friction coefficient μ defines the contact state. The friction coefficient μ = ∞, indicating that the ice layer is embedded in the road surface in a tightly connected state without spraying ice suppression materials, and the interlayer state is continuous. The friction coefficient μ = 0, the state of approximately free sliding between the ice and the road surface, and other contact states in the two ideal states are simulated using the friction coefficient μ variable parameter.

[0024] The beneficial effects of the present invention are:

[0025] 1. The present invention adopts the perspective of mechanical simulation to more essentially explain the dynamic interaction of interlayer contact on ice bonding strength, and more intuitively makes accurate judgments on the changes in the contact structure between ice and road surface layers, thus overcoming the shortcomings of traditional test evaluation methods, such as large errors, high costs, and a certain degree of waste of resources.

[0026] 2. The present invention can provide a reference for determining the optimal icing strength value of the ice suppression material in contact with the ice-pavement layer by setting different aggregate discharge heights, aggregate gaps, ambient temperatures, and ice thicknesses, thereby improving the ice suppression efficiency.

[0027] 3. The method provided by the present invention can provide a variety of forms and methods for the study of ice-suppressing pavement. BRIEF DESCRIPTION OF THE DRAWINGS

[0028] Figure 1 It is a schematic diagram of the mechanical model of the present invention;

[0029] Figure 2 It is the displacement boundary condition and force analysis diagram of the present invention;

[0030] Figure 3 It is a schematic diagram of grid division of the present invention;

[0031] Figure 4 The strain cloud diagram of the ice layer when the interlayer friction coefficient μ=∞ in the present invention; wherein (a) is the tensile strain in the X direction of the ice layer; (b) is the tensile strain in the Y direction of the ice layer; (c) is the maximum shear strain in the ice layer;

[0032] Figure 5 The strain cloud diagram of the ice layer when the interlayer friction coefficient μ=0 of the present invention; wherein (a) is the tensile strain in the X direction of the ice layer; (b) is the tensile strain in the Y direction of the ice layer; (c) is the maximum shear strain in the ice layer;

[0033] Figure 6Schematic diagram of strain values ​​in ice layers at different contact states of the present invention;

[0034] Figure 7 This is a diagram showing the influence of aggregate distribution on shear strain in ice layer according to the present invention;

[0035] Figure 8 This is a diagram showing the influence of ambient temperature and ice layer thickness on the shear strain in the ice layer according to the present invention. DETAILED DESCRIPTION

[0036] In order to make the technical means, creative features, objectives and effects achieved by the present invention easy to understand, the present invention is further described below in conjunction with specific embodiments and diagrams.

[0037] The present invention provides a mechanical simulation method for the contact between ice and road surface layers of an ice suppression material. A two-dimensional extended finite element model of an ice-road surface composite structure is established by using ABAQUS software. The model parameters include an assumed basis, an initial external force, a model structure, a mesh type, a mesh density, material properties, a displacement boundary condition, and a contact type. The numerical influence of the pavement macro texture (exposed height of aggregate, gap between aggregates), the ice formation process (thickness of ice layer, ambient temperature), etc. on the icing strength is analyzed to determine the optimal icing strength value and improve the ice suppression efficiency.

[0038] In order to facilitate the calculation and analysis of the mechanical response of road ice suppression, the assumptions are as follows:

[0039] ① Asphalt mortar, aggregate and ice layer are all continuous, isotropic linear elastic materials. The stress and deformation are all within the elastic range. Their elastic parameters are characterized by elastic modulus E and Poisson's ratio μ, and their mechanical properties obey Hooke's law.

[0040] Hooke's law states that when an object is subjected to an external force and the stress is not greater than the yield stress σ0, the stress σ1 and the strain ε1 are in a positive linear relationship.

[0041] σ1=Eε1

[0042] Wherein, E is the elastic modulus (or Young's modulus).

[0043] ②The fixed contact between aggregate and asphalt mortar is completely continuous.

[0044] ③ The ice surface and the road surface will not invade each other when in contact, and the layers will maintain contact without gaps.

[0045] ④ Ignore minor factors such as the vehicle's lateral force and impact force, and focus on vertical loads and horizontal loads.

[0046] In this embodiment, the initial external force is divided into vertical load and horizontal load. The vertical load acts on the road surface in accordance with the standard single-axle double-wheel BZZ-100 uniform load, with the direction vertically downward, vertical axle load P = 100 / 4 = 25kN, single wheel ground pressure p = 0.7MPa, equivalent circle diameter d = 213mm, and wheel load spacing is 1.5d. According to the area equivalence principle, the contact surface close to the ellipse is equivalent to a square contact surface, and the formula is: Calculation shows that the side length of the equivalent square is 189mm.

[0047] While fully considering the vertical load, the horizontal friction force during driving and braking should also be considered. The magnitude of the force is determined by the friction coefficient of the road surface when it is icy. The friction coefficient f of the icy road surface is 0.15. According to the formula q=fp, the horizontal pressure q is 0.105MPa.

[0048] The wheel-road contact area is an equivalent square with a side length of L = 189mm. When analyzing the road force, the road needs to be simplified due to modeling limitations. Therefore, the single wheel uniform load area is taken as the asphalt road model size. The conclusion of the study on the influence of the overall size of the asphalt road on the microstructural stress shows that the calculation results of various stress values ​​in different model sizes only differ by about 5%, and the size effect has no significant effect on the model calculation results. In order to calculate and ensure accuracy, the two-dimensional model size is taken as 200mm (length) × 40mm (depth), and in terms of depth, only the asphalt upper layer is taken as the main body of the investigation.

[0049] According to the conclusion of the numerical analysis of the microstructure of the texture characteristics of asphalt pavement (using multiple square aggregates with a size of 10mm×10mm), aggregates have the function of dispersing stress loads and are the skeleton foundation of asphalt mixtures. The multiple aggregate model is more in line with the actual situation than the single aggregate model. For multiple aggregates, the number of aggregates has little effect on the stress and strain inside the ice layer. Therefore, three square aggregates are used, with a side length of 10mm and an exposed height of 0.5-2mm. The thickness of the ice layer is analyzed and calculated using early morning thin ice, which is generally 3-9mm thick.

[0050] The mesh type is eight-node quadratic plane strain reduced integration element CPE8R.

[0051] The grid density is determined by the contact position between the aggregate, ice layer and asphalt surface. A non-homogeneous grid is used for free division, with a denser division at the aggregate and a gradually sparser division at other locations. The specific division is shown in Table 1.

[0052] Table 1 Model grid parameters

[0053]

[0054] The model parameters are divided into aggregate parameters, asphalt mixture and ice layer parameters. Asphalt mixture is a three-phase composite material composed of asphalt mortar, aggregate and voids. Studies have shown that the strength and elastic strength of aggregate itself are much higher than that of asphalt mixture and the volume proportion of aggregate in asphalt mixture is relatively large, so it is necessary to determine the parameters of aggregate separately. The corresponding mechanical parameters can be determined by the uniaxial compression deformation test of aggregate rock. According to certain experience, most of the rocks selected in asphalt mixture are granite, basalt and other rocks with high strength. After comprehensive consideration, the elastic modulus of the selected aggregate is 60000MPa and the Poisson's ratio is 0.15. Asphalt mixture and ice layer are highly sensitive to temperature. When affected by solar radiation and climate change, the elastic modulus fluctuates greatly. In the coupling of structure and temperature, in order to reflect the changes of materials at different temperatures, different parameters of materials at different temperatures need to be input in the structural analysis. The parameters of asphalt mixture and ice layer are comprehensively determined by referring to the material design parameters in Appendix E of "Highway Asphalt Pavement Design Specification" (JTG D50-2006) and related research, as shown in Table 2.

[0055] Table 2 Material performance parameters

[0056]

[0057] The displacement boundary conditions are that there is no displacement in the X and Y directions at the bottom of the model and it is fully constrained (U1=U2=0), and there is no displacement in the X direction on both sides of the model and it is fully constrained (U1=0).

[0058] The contact type uses a penalty friction formula that allows relative sliding (called elastic sliding) on ​​the "bonded" state surface to simulate the contact surface, ensuring that the displacement and vertical stress on the contact surface can be continuously transmitted. Coulomb friction is used to simulate the tangential action between the contact surfaces, and the friction coefficient μ defines the contact state. The friction coefficient μ = ∞, indicating that the ice layer is embedded in the road surface in a tightly connected state without spraying ice suppression materials, and the interlayer state is continuous. The friction coefficient μ = 0, the state of free sliding between the ice and the road surface, and other contact states in the two ideal states are simulated using the friction coefficient μ variable parameter.

[0059] Under the action of the selected standard axle load, the temperature is 0℃, the exposed height of the aggregate is 0.5mm, the thickness of the ice layer is 5mm, and the interval between the aggregates is 5mm. Five contact states between ice and the road surface are proposed: μ = 0 (free sliding), μ = 0.2, μ = 0.5, μ = 0.8, μ = ∞ (completely continuous), and the stress and strain conditions inside the ice layer under different contact states are analyzed, as shown in Table 3.

[0060] Table 3 Internal strain of ice layer under different ice-road contact states

[0061]

[0062] When the contact between the ice and road surface changes from rough to smooth, both the tensile strain and the shear strain increase, with the maximum tensile strain increasing by 390-420% and the shear strain increasing by 610%. This indicates that the shear strain changes greatly under different contact conditions, so when the ice layer is subjected to external force, it is mainly damaged by shear strain. When μ<0.5, the growth rate of both tensile strain and shear strain increases significantly. According to the brittle failure theory of ice layers, the chain strength of ice mainly depends on the strength of the weakest chain. When some cracks appear in the ice layer, a small stress will also cause a large change in strength, and the cracks will spread and cause overall crack damage.

[0063] Compare the maximum tensile strain and shear strain in the XY direction. Figure 6 It can be seen that when subjected to external forces, the shear strain of the ice layer is always greater than the tensile strain and does not change with the interlayer contact state. The damage of the ice layer is mainly caused by the shear strain, which causes the overall change. Studies have shown that the ultimate tensile strain and shear strain of ice are 2.1×10 -4 , 2.3×10 -4 When the ice-road surface is in a continuous state (μ=∞), the maximum tensile strain is 0.675×10 -4 , the maximum shear strain is 0.893×10 -4 , are all less than the ultimate failure strain of ice. Therefore, when the external force is constant and the ice-road surface is in a rough state, it has no ice suppression effect. When the ice-road surface is smooth (μ=0), the maximum tensile strain is 3.518×10 -4 , which is 420% higher than the original road surface, and the maximum shear strain is 6.352×10 -4 , an increase of 610% compared with the original road surface, and both are greater than the ice limit failure strain, which can effectively improve the ice suppression effect.

[0064] Under the selected standard axle load, the temperature is 0℃, the ice layer thickness is 5mm, the interlayer contact state is μ=0, the aggregate exposure height is 0.5~2mm, and the aggregate gap is 2~11mm. After numerical analysis, the influence of aggregate distribution on ice layer strain is shown in Figure 7 .

[0065] from Figure 7 It can be seen that the shear strain in the ice layer gradually increases with the increase of the exposed height of the aggregate. When the aggregate gap is 5 mm, when the exposed height of the aggregate increases from 0.5 mm to 2 mm, the maximum shear strain increases by 2.4×10 -4 , indicating that the greater the exposed height of the aggregate, the more conducive it is to the material's ice suppression, but the exposed aggregate should not be too much, otherwise it will affect the road surface flatness. In addition, the shear strain inside the ice layer gradually decreases with the increase of the aggregate gap, and when the aggregate gap is 8mm, the strain value changes little. When the exposed height of the aggregate is 0.5mm, when the aggregate gap increases from 2mm to 11mm, the maximum shear strain decreases by 1.35×10-4 , indicating that the increase in aggregate gaps makes the ice suppression effect gradually worse.

[0066] Under the selected standard axle load, the exposed height of aggregate is 0.5mm, the gap between aggregates is 5mm, the interlayer contact state is smooth road surface μ=0, the ambient freezing temperature is -15~0℃, and the ice thickness is 3~9mm. After numerical analysis, the influence of ambient temperature and ice thickness on the shear strain in the ice layer is shown in Figure 8 .

[0067] from Figure 8 It can be seen that the shear strain value inside the ice layer gradually increases with the increase of ambient temperature, and the change range is large. When the ice layer thickness is 5 mm, when the freezing temperature changes from -15℃ to 0℃, the maximum shear strain increases by 3.57×10 -4 . As the freezing temperature is lower, the ice lattice strength is greater, and the ability to resist shear deformation is stronger. Therefore, at lower temperatures, the shear strain is smaller, and external force must be used to remove ice. In addition, the shear strain inside the ice layer gradually decreases with the increase of ice thickness, and the change range is small. When the freezing temperature is 0℃, when the ice thickness increases from 3mm to 9mm, the maximum shear strain decreases by 2.43×10 -4 Due to the brittle failure of the ice layer, when the crack expands, the expansion speed is slower when the ice layer is thicker and the deformation resistance is higher, and the main form of failure is shear failure.

[0068] The above shows and describes the basic principles and main features of the present invention and the advantages of the present invention. It should be understood by those skilled in the art that the present invention is not limited to the above embodiments. The above embodiments and descriptions are only for explaining the principles of the present invention. Without departing from the spirit and scope of the present invention, the present invention may have various changes and improvements, which fall within the scope of the present invention to be protected. The scope of protection of the present invention is defined by the attached claims and their equivalents.

Claims

1. A mechanical simulation method for contact between ice suppression material and ice-pavement layer, characterized by: A two-dimensional extended finite element model of the ice-pavement composite structure was established using ABAQUS software. The model parameters included assumed basis, initial external force, model structure, mesh type, mesh density, material properties, displacement boundary conditions and contact type. The numerical influence of pavement macrotexture and ice formation process on icing intensity was analyzed to determine the optimal icing intensity value and improve ice suppression efficiency.

2. The mechanical simulation method of ice suppression material contact between ice and road surface according to claim 1, characterized in that: The assumptions are as follows: ① Asphalt mortar, aggregate and ice layer are all continuous, isotropic linear elastic materials. The stress and deformation are all within the elastic range. Their elastic parameters are characterized by elastic modulus E and Poisson's ratio μ, and their mechanical properties obey Hooke's law. ② The fixed contact between aggregate and asphalt mortar is completely continuous; ③ The ice surface and the road surface will not invade each other when in contact, and the layers will maintain contact without gaps; ④ Ignore minor factors such as the vehicle's lateral force and impact force, and focus on vertical loads and horizontal loads.

3. The mechanical simulation method of ice suppression material contact between ice and road surface according to claim 1, characterized in that: The initial external force is divided into vertical load and horizontal load; the vertical load acts on the road surface according to the standard single-axle double-wheel uniform load, and the direction is vertically downward; the horizontal load is determined by the friction coefficient of the road surface when icy, and the horizontal pressure is obtained according to the formula q=fp.

4. The method for mechanical simulation of ice suppression material contact between ice and road surface according to claim 1, characterized in that: The model structure is a layered structure, which includes a thin ice layer and an asphalt surface layer from top to bottom.

5. The method for mechanical simulation of ice suppression material contact between ice and road surface according to claim 1, characterized in that: The mesh type is an eight-node quadratic plane strain reduced integration element.

6. The mechanical simulation method of ice suppression material contact between ice and road surface according to claim 1, characterized in that: The grid density is determined by the contact position between the aggregate, the ice layer and the asphalt surface, and is freely divided by a non-homogeneous grid, with a denser division at the aggregate and a gradually sparser division at other positions.

7. The method for mechanical simulation of ice suppression material contact between ice and road surface according to claim 1, characterized in that: The material properties are aggregate parameters, asphalt mixture and ice layer parameters.

8. The method for mechanical simulation of ice suppression material contact between ice and road surface according to claim 1, characterized in that: The displacement boundary conditions are that there is no displacement in the X and Y directions at the bottom of the model and it is fully constrained; there is no displacement in the X direction on both sides of the model and it is fully constrained.

9. The method for mechanical simulation of ice suppression material contact between ice and road surface according to claim 1, characterized in that: The contact type adopts a penalty friction formula that allows relative sliding of surfaces in a "bonded" state to simulate the contact surface, ensuring that the displacement and vertical stress on the contact surface can be continuously transmitted, and uses Coulomb friction to simulate the tangential action between the contact surfaces. The friction coefficient μ defines the contact state.

10. The mechanical simulation method of ice suppression material contact between ice and road surface according to claim 9, characterized in that: The friction coefficient μ=∞, indicating that the anti-icing material is not sprayed, the ice layer is embedded in the road surface in a tightly connected state, and the layers are continuous; the friction coefficient μ=0, the ice and the road surface are in a state of approximately free sliding, and other contact states between the two ideal states are simulated using the friction coefficient μ variable parameter.

Images