A method for calculating the spalling life of thermal barrier coatings for turbine blades

Abstract

The present invention discloses a method for calculating the spalling life of thermal barrier coating for turbine blades. The method uses the surface node information of turbine blades without thermal barrier coating as input, avoids the generation of complex coating geometric models and finite element meshes on the blade surface, realizes rapid and accurate calculation of the spalling life of the coating, and provides a method tool for the life design and life management of key components with thermal barrier coating.

Description

Technical Field

[0001] The present disclosure relates to the field of aeroengines, and in particular to a method for calculating the spalling life of a thermal barrier coating for a turbine blade. Background Art

[0002] Thermal barrier coating is an effective thermal protection technology, which is widely used in hot end parts of aircraft engines and gas turbines, such as turbine blades and guide vanes. It can improve the temperature resistance of the above structures by about 170℃, thereby extending the service life of the parts and improving the overall performance and thermal efficiency of the engine. At present, common thermal barrier coatings all adopt a double-layer structure: the outermost layer is a yttria-stabilized zirconia ceramic layer, which has low thermal conductivity and good high-temperature stability and mainly plays a heat-insulating role; a multi-element metal bonding layer is introduced between the ceramic layer and the high-temperature alloy substrate to alleviate the thermal expansion mismatch between the ceramic and the substrate and improve the bonding strength. Under high temperature environment, elements such as Al in the bonding layer react with oxygen that penetrates the ceramic layer to form a thin layer of thermally grown oxide (thermally grown oxide layer) at the interface between the ceramic and the metal, which can delay the further penetration of oxygen and prevent oxidation corrosion of the substrate. At the same time, the thermal expansion coefficient of the thermally grown oxide layer is smaller than that of the adjacent ceramic layer and bonding layer, which destroys the mechanical compatibility inside the coating system. When it grows to a certain extent, it will cause the coating to peel off.

[0003] Although thermal barrier coatings have been used for decades, their premature flaking and failure during service is still a primary problem that plagues the academic and engineering communities. Especially for turbine blades, once the thermal barrier coating on the surface is peeled off, the base alloy will be exposed to a high-temperature corrosive gas environment that exceeds the material's designed temperature resistance, which can easily cause blade ablation and fracture, seriously endangering the engine's safety, reliability and economy. How to accurately predict the service life of thermal barrier coatings and maximize their performance advantages and potential has become one of the key technologies faced by coating material selection, blade structure design, engine life management, and maintenance assurance.

[0004] The current prediction of the spalling life of thermal barrier coatings mainly adopts the calculation method proposed by Meier et al. (see Meier S.M., Nissley DM, Sheffler KD, et al. Thermal barrier coating life prediction model development. Journal of Engineering for Gas Turbines and Power, 1992, 114: 258-263.). This method assumes that the damage of thermal barrier coating depends on the ratio of its internal effective strain to failure strain, where the effective strain needs to use a specific function form (such as cosine) to describe the ceramic-metal interface morphology, and is extracted through the microscopic finite element analysis of the "ceramic layer-thermal growth oxide layer-bonding layer-substrate" system. The failure strain is defined as the strain corresponding to the spalling after only one thermal cycle, which decreases with the increase of the thickness of the thermal growth oxide layer and the effective strain. On this basis, the number of load cycles corresponding to the damage reaching 1 is used as the spalling life of the thermal barrier coating.

[0005] The limitations of the above method are mainly reflected in the following aspects: the real turbine blade profile is a complex three-dimensional surface, and it is very difficult to generate a thermal barrier coating geometric model with a specific interface morphology on its surface; the thickness of the turbine blade substrate is generally 1 to 3 mm, while the thickness of the thermally grown oxide layer in the coating is only 0.5 to 5 μm, and the size difference between the two is 1000 times. The cross-scale finite element modeling process of this magnitude is too cumbersome; in order to calculate the damage accumulation process, it is necessary to repeatedly solve the effective strain under different thermally grown oxide layer thicknesses, which requires huge calculations; the different effects of oxidation and mechanical factors on coating spalling are not explicitly considered in the damage calculation process, and the scope of application is limited. This makes it difficult to promote and apply the existing thermal barrier coating spalling life calculation method in actual turbine blade engineering design. How to avoid generating complex thermal barrier coating geometric models and finite element meshes on the surface of turbine blades and realize fast and accurate calculation of thermal barrier coating spalling life has become the core problem to be solved by the present invention. Summary of the invention

[0006] In response to the above-mentioned problems, the purpose of the present invention is to provide a method for calculating the spalling life of thermal barrier coatings for turbine blades, in order to achieve a rapid and accurate estimation of the service life of the thermal barrier coatings, and to provide a method tool for the life design and life management of key components with thermal barrier coatings.

[0007] To achieve the above object, the present disclosure provides a method for calculating the spalling life of a thermal barrier coating for a turbine blade, comprising the following steps:

[0008] Step 1: Acquire surface node information of a turbine blade without a thermal barrier coating, wherein the surface node information includes principal stress, principal strain, direction vector, peak temperature, valley temperature, and peak temperature holding time of the surface node;

[0009] Step 2: Determine the peak total strain and the valley total strain of the surface node in the in-plane direction according to the principal stress, the principal strain and the direction vector;

[0010] Step 3: Determine the peak mechanical strain and the valley mechanical strain of the ceramic layer, the thermally grown oxide layer and the bonding layer in the thermal barrier coating in the in-plane direction according to the peak total strain, the valley total strain, the peak temperature and the valley temperature;

[0011] Step 4: determining the mechanically driven damage generated by the thermal barrier coating according to the peak mechanical strain and the valley mechanical strain of the bonding layer in the in-plane direction;

[0012] Step 5: Calculating the oxidation-driven damage generated by the thermal barrier coating in the current cycle according to the peak temperature, the corresponding peak temperature holding time and the number of cycles in the current cycle;

[0013] Step 6: Determine the total damage of the thermal barrier coating in the current cycle according to the mechanically driven damage and the oxidation driven damage;

[0014] Step 7: determining a damage threshold of the thermal barrier coating for peeling off according to the valley mechanical strain of the ceramic layer in the in-plane direction;

[0015] Step 8: If the total damage does not reach the damage threshold, the number of cycles of the current cycle is increased by 1, and steps 4 to 7 are repeated; if the total damage reaches the damage threshold, it is determined that the thermal barrier coating at the surface node has peeled off, and the corresponding surface node position and the number of cycles experienced are output, and steps 1 to 7 are repeated for the next surface node until it is determined that the thermal barrier coating at all surface nodes has peeled off, and the thermal barrier coating peeling life distribution of the turbine blade surface area is obtained.

[0016] Optionally, determining the peak total strain and the valley total strain of the surface node in the in-plane direction according to the principal stress, the principal strain and the direction vector includes:

[0017] Determine the direction vector corresponding to the principal stress with the smallest absolute value as the surface normal vector;

[0018] The two peak load principal strains and valley load principal strain components whose direction vectors are inconsistent with the surface normal vector are taken as the total in-plane strains of the surface nodes;

[0019] Among the principal strains at the peak load, the larger value of the total in-plane strain of the surface node is taken as the peak total strain of the node in the in-plane direction;

[0020] In the valley load principal strain, the larger value of the in-plane total strain of the surface node is taken as the valley total strain of the node in the in-plane direction.

[0021] Optionally, determining the peak mechanical strain and the valley mechanical strain of the ceramic layer, the thermally grown oxide layer and the bonding layer in the thermal barrier coating in the in-plane direction according to the peak total strain, the valley total strain, the peak temperature and the valley temperature comprises:

[0022] Calculate the first thermal strain of the ceramic layer, the thermally grown oxide layer and the bonding layer when the temperature changes from room temperature to the peak temperature and the second thermal strain when the temperature changes from room temperature to the valley temperature according to the peak temperature, the valley temperature and the thermal expansion coefficients of the ceramic layer, the thermally grown oxide layer and the bonding layer in the thermal barrier coating;

[0023] Calculating the residual strain of the ceramic layer, the thermally grown oxide and the bonding layer when the stress-free initial temperature changes to room temperature according to the stress-free initial temperature of the thermal barrier coating and the thermal expansion coefficient of the turbine blade;

[0024] The peak mechanical strain and the valley mechanical strain of the ceramic layer, the thermally grown oxide and the bonding layer in the thermal barrier coating in the in-plane direction are determined according to the peak total strain, the valley total strain, the first thermal strain, the second thermal strain and the residual strain.

[0025] Optionally, the calculating, according to the peak temperature, the valley temperature, and the thermal expansion coefficients of the ceramic layer, the thermally grown oxide layer, and the bonding layer in the thermal barrier coating, a first thermal strain of the ceramic layer, the thermally grown oxide layer, and the bonding layer when the temperature changes from room temperature to the peak temperature and a second thermal strain when the temperature changes from room temperature to the valley temperature comprises:

[0026] Calculate the first thermal strain of the ceramic layer, the thermally grown oxide and the bonding layer when the temperature changes from room temperature to the peak temperature and the second thermal strain when the temperature changes from room temperature to the valley temperature according to the following formula;

[0027]

[0028] in, represents the first thermal strain of layer i, α i (T) represents the thermal expansion coefficient of layer i, T peak represents the peak temperature, T0 represents the room temperature, represents the second thermal strain of layer i, T valley represents the valley temperature. When the subscript i is 1, it represents the ceramic layer; when i is 2, it represents the thermally grown oxide layer; when i is 3, it represents the bonding layer.

[0029] Optionally, the calculating, based on the stress-free initial temperature of the thermal barrier coating and the thermal expansion coefficient of the turbine blade, the residual strain of the ceramic layer, the thermally grown oxide layer and the bonding layer when the stress-free initial temperature changes to room temperature comprises:

[0030] Calculate the residual strain of the ceramic layer, the thermally grown oxide layer and the bonding layer when the stress-free initial temperature changes to room temperature according to the following formula;

[0031]

[0032] represents the residual strain of layer i when it changes from the stress-free initial temperature to room temperature, α s (T) represents the thermal expansion coefficient of the turbine blade, α i (T) represents the thermal expansion coefficient of layer i, T free represents the stress-free initial temperature of the thermal barrier coating, T0 represents room temperature, the subscript i is 1 for the ceramic layer, i is 2 for the thermally grown oxide layer, and i is 3 for the bonding layer.

[0033] Optionally, determining the peak mechanical strain and the valley mechanical strain of the ceramic layer, the thermally grown oxide, and the bonding layer in the thermal barrier coating in the in-plane direction according to the peak total strain, the valley total strain, the first thermal strain, the second thermal strain, and the residual strain comprises:

[0034] The peak mechanical strain and valley mechanical strain of the ceramic layer, the thermally grown oxide layer and the bonding layer in the thermal barrier coating in the in-plane direction are determined according to the following formulas;

[0035]

[0036] in,

[0037] represents the peak mechanical strain of layer i,

[0038] represents the valley mechanical strain of layer i,

[0039] represents the peak total strain of the matrix,

[0040] represents the total valley strain of the matrix,

[0041] represents the first thermal strain of layer i,

[0042] represents the second thermal strain of layer i,

[0043] represents the residual strain of layer i,

[0044] When the subscript i is 1, it represents a ceramic layer, when i is 2, it represents a thermally grown oxide layer, and when i is 3, it represents a bonding layer.

[0045] Optionally, determining the mechanically driven damage generated by the thermal barrier coating according to the peak mechanical strain and the valley mechanical strain of the bonding layer in the in-plane direction includes:

[0046] Calculating the range of mechanical strain generated in the in-plane direction of the bonding layer according to the peak mechanical strain and the valley mechanical strain of the bonding layer in the in-plane direction;

[0047] The mechanically driven damage of the thermal barrier coating is calculated based on the range of mechanical strain generated by the bonding layer in the in-plane direction and the number of cycles of the current cycle.

[0048] Optionally, calculating the range of mechanical strain generated by the bonding layer in the in-plane direction according to the peak mechanical strain and the valley mechanical strain of the bonding layer in the in-plane direction includes:

[0049] The range of mechanical strain generated in the bonding layer in the in-plane direction of the thermal barrier coating is determined according to the following formula;

[0050]

[0051] in, It represents the range of mechanical strain generated in the bonding layer in the in-plane direction. represents the peak mechanical strain of the bonding layer, Indicates the valley value of the mechanical stress of the bonding layer.

[0052] Optionally, calculating the mechanically driven damage of the thermal barrier coating according to the range of mechanical strain generated by the bonding layer in the in-plane direction and the number of cycles of the current cycle includes:

[0053] The mechanically driven damage of thermal barrier coatings is determined according to the following formula;

[0054]

[0055] Among them, D cyc represents the mechanically driven damage of thermal barrier coatings, represents the range of mechanical strain produced in the bonding layer in the in-plane direction, A and b represent material constants, and N represents the number of cycles of the current cycle.

[0056] Optionally, the calculating, according to the peak temperature, the corresponding peak temperature holding time and the number of cycles of the current cycle, the oxidation driven damage generated by the thermal barrier coating in the current cycle comprises:

[0057] Calculating the thickness of the thermally grown oxide layer in the thermal barrier coating of the current cycle according to the peak temperature, the corresponding peak temperature holding time and the number of cycles of the current cycle;

[0058] The oxidation driven damage generated by the thermal barrier coating in the current cycle is calculated according to the thickness of the thermally grown oxide layer in the thermal barrier coating.

[0059] Optionally, calculating the thickness of the thermally grown oxide layer in the thermal barrier coating of the current cycle according to the peak temperature, the corresponding peak temperature holding time and the number of cycles of the current cycle includes:

[0060] According to the following formula, the thickness of the thermally grown oxide layer in the thermal barrier coating of the current cycle is calculated;

[0061]

[0062] Where δ represents the thickness of the thermally grown oxide layer in the thermal barrier coating in the previous cycle, T peak represents the peak temperature, t hold represents the corresponding holding time, N represents the number of cycles of the current cycle, ΔH and T ref represents the material constant, R represents the unified gas constant, n(T peak ) is the temperature-dependent material constant.

[0063] Optionally, calculating the oxidation-driven damage generated by the thermal barrier coating in the current cycle according to the thickness of the thermally grown oxide layer in the thermal barrier coating comprises:

[0064] The oxidation-driven damage generated by the thermal barrier coating in the current cycle is calculated according to the following formula:

[0065]

[0066] D ox represents the oxidation driven damage generated by the thermal barrier coating in the current cycle, δ represents the thickness of the thermally grown oxide layer in the thermal barrier coating in the previous cycle, and δ0 and m represent material constants.

[0067] Optionally, the total damage of the thermal barrier coating generated in the current cycle is determined based on the mechanically driven damage and the oxidation driven damage, including:

[0068] The total damage of the thermal barrier coating in the current cycle is calculated according to the following formula:

[0069] D N =D ox +D cyc -kD ox D cyc ;

[0070] Among them, D N It represents the total damage of thermal barrier coating in the current cycle, D cyc represents the mechanically driven damage of thermal barrier coating, D ox represents the oxidation-driven damage caused by the thermal barrier coating in the current cycle, and k represents the material constant.

[0071] Optionally, determining the damage threshold of spalling of the thermal barrier coating according to the valley mechanical strain of the ceramic layer in the in-plane direction includes:

[0072] The damage threshold of thermal barrier coating spalling is calculated according to the following formula;

[0073]

[0074] Among them, D spall The damage threshold of thermal barrier coating peeling occurs. represents the valley mechanical strain of the ceramic layer in the in-plane direction, h represents the thickness of the ceramic layer, ν1(T valley ) represents the Poisson’s ratio of the ceramic layer in the in-plane direction at the valley temperature, and R0 represents the material constant.

[0075] The beneficial effects of the present disclosure are as follows: the method for calculating the spalling life of thermal barrier coating for turbine blades provided by the present disclosure uses the surface node information of turbine blades without thermal barrier coating as input, avoids the generation of complex coating geometric models and finite element meshes on the blade surface, and realizes rapid and accurate calculation of the coating spalling life. It can be directly used as post-processing of the existing turbine blade finite element analysis process, avoids the cumbersome cross-scale modeling process of the "ceramic layer-thermal growth oxide layer-bonding layer-blade" system from micro to macro, significantly reduces the workload of designers, and provides method tools for the life design and life management of key components with thermal barrier coatings. BRIEF DESCRIPTION OF THE DRAWINGS

[0076] The accompanying drawings illustrate exemplary embodiments of the present disclosure and together with the description serve to explain the principles of the present disclosure. These drawings are included to provide a further understanding of the present disclosure and are incorporated in and constitute a part of this specification.

[0077] Figure 1 Flow chart of the steps in the method for calculating the spallation life of thermal barrier coatings for turbine blades. DETAILED DESCRIPTION

[0078] The present disclosure is further described in detail below in conjunction with the accompanying drawings and embodiments. It is to be understood that the specific embodiments described herein are only used to explain the relevant content, rather than to limit the present disclosure. It is also necessary to explain that, for ease of description, only the parts related to the present disclosure are shown in the accompanying drawings.

[0079] It should be noted that, in the absence of conflict, the embodiments and features in the embodiments of the present disclosure may be combined with each other.

[0080] See also Figure 1 , this embodiment includes:

[0081] A method for calculating the spalling life of a thermal barrier coating for a turbine blade comprises the following steps:

[0082] Step 1: Obtain the surface node information of the turbine blade without thermal barrier coating, the surface node information including the principal stress, principal strain, direction vector, peak temperature, valley temperature and peak temperature holding time of the surface node;

[0083] Step 2: Determine the peak total strain and valley total strain of the surface nodes in the in-plane direction based on the principal stress, principal strain and direction vector;

[0084] Step 3: Determine the peak mechanical strain and valley mechanical strain of the ceramic layer, the thermally grown oxide layer and the bonding layer in the thermal barrier coating in the in-plane direction according to the peak total strain, the valley total strain, the peak temperature and the valley temperature;

[0085] Step 4: Determine the mechanically driven damage generated by the thermal barrier coating based on the peak mechanical strain and valley mechanical strain of the bonding layer in the in-plane direction;

[0086] Step 5: Calculate the oxidation-driven damage generated by the thermal barrier coating in the current cycle according to the peak temperature, the corresponding peak temperature holding time and the number of cycles in the current cycle;

[0087] Step 6: Determine the total damage of the thermal barrier coating in the current cycle according to the mechanically driven damage and the oxidation driven damage;

[0088] Step 7: Determine the damage threshold of the thermal barrier coating for peeling according to the valley mechanical strain of the ceramic layer in the in-plane direction;

[0089] Step 8: If the total damage does not reach the damage threshold, the number of cycles of the current cycle is increased by 1, and steps 4 to 7 are repeated; if the total damage reaches the damage threshold, it is determined that the thermal barrier coating at the surface node has peeled off, and the corresponding surface node position and the number of cycles experienced are output. Steps 1 to 7 are repeated for the next surface node until it is determined that the thermal barrier coating at all surface nodes has peeled off, and the thermal barrier coating peeling life distribution of the turbine blade surface area is obtained.

[0090] For each surface node of the turbine blade, mechanically driven damage calculation, oxidation driven damage calculation, total damage and spalling life calculation are performed in sequence.

[0091] The calculation steps of mechanically driven damage are as follows:

[0092] The first step is to determine the peak total strain of the surface node in the in-plane direction based on the input principal stress, principal strain and direction vector of the turbine blade surface node. Total valley strain Among them, the superscript “tot” represents the total strain, the subscript “s” represents the turbine blade surface without thermal barrier coating, “peak” represents the peak load, and “valley” represents the valley load;

[0093] In the second step, the peak total strain of the surface nodes in the in-plane direction is Total valley strain Peak temperature T peak , valley temperature T valley , calculate the peak mechanical strain of the ceramic layer, thermally grown oxide layer, and bonding layer in the thermal barrier coating in the in-plane direction Valley mechanical strain Wherein, the superscript “m” indicates mechanical strain, the subscript i is 1 for the ceramic layer, 2 for the thermally grown oxide layer, and 3 for the bonding layer;

[0094] The third step is to calculate the range of mechanical strain generated in the in-plane direction of the bonding layer based on the peak mechanical strain and valley mechanical strain of the bonding layer in the in-plane direction obtained in the second step. Then calculate the mechanically driven damage D of the thermal barrier coating generated by the current cycle N cyc .

[0095] The steps for calculating oxidation-driven damage are as follows:

[0096] The fourth step is to calculate the peak temperature T of the surface node. peak , the corresponding holding time t hold and the cycle number N of the current cycle, calculate the thickness δ of the thermally grown oxide layer of the current cycle;

[0097] Step 5: Calculate the oxidation-driven damage D generated by the thermal barrier coating in the current cycle based on the thickness δ of the thermally grown oxide layer obtained in step 4. ox .

[0098] The calculation steps of total damage and spalling life are as follows:

[0099] Step 6: Based on the mechanically driven damage D obtained in step 3 cyc and the oxidation-driven damage D obtained in step 5 ox , calculate the total damage D of the thermal barrier coating in the current cycle N ;

[0100] Step 7: According to the valley mechanical strain of the ceramic layer obtained in step 2 Calculation of the damage threshold D for thermal barrier coating to peel offspall ;

[0101] Step 8: Determine the total damage D N Whether the damage threshold D is reached spall If not, the cycle number N becomes N+1, and steps 3 to 7 are repeated; if yes, the thermal barrier coating at the node peels off, and the corresponding surface node position and the number of cycles N (i.e., peeling life) experienced are output, and then steps 1 to 7 are repeated for the next surface node until the thermal barrier coating at all surface nodes peels off.

[0102] In the first step, the peak total strain and valley total strain of the surface nodes in the in-plane direction are calculated as follows:

[0103] (1.1) Determine the direction vector corresponding to the principal stress with the smallest absolute value as the surface normal vector;

[0104] (1.2) The two peak load principal strains and valley load principal strain components whose direction vectors are inconsistent with the surface normal vector are taken as the total in-plane strains of the surface nodes;

[0105] (1.3) Among the peak load principal strains, the larger value of the in-plane total strain of the surface node is taken as the peak total strain of the node in the in-plane direction.

[0106] (1.4) Among the principal strains of the valley load, the larger value of the total in-plane strain of the surface node is taken as the total valley strain of the node in the in-plane direction.

[0107] In the second step, the peak mechanical strain and valley mechanical strain of the ceramic layer, thermally grown oxide layer, and bonding layer in the thermal barrier coating in the in-plane direction are calculated as follows:

[0108] (2.1) According to the peak temperature T of the surface node peak , valley temperature T valley , and the thermal expansion coefficient α of each layer of the thermal barrier coating i (T) (reference temperature is room temperature T0, T is temperature, and T is a temperature-related material constant), the following formula is used to calculate the change of the ceramic layer, thermally grown oxide layer, and bonding layer from T0 to T peak Thermal strain From T0 to T valley Thermal strain The superscript "th" indicates thermal strain:

[0109]

[0110]

[0111] (2.2) According to the stress-free initial temperature T of the thermal barrier coating free , and the thermal expansion coefficient of the turbine blade α s (T) (reference temperature is room temperature T0, T is temperature, and is a temperature-related material constant), and T is calculated by the following formula free Residual strains of ceramic layer, thermally grown oxide layer and bonding layer at T0 The superscript "r" represents the residual strain:

[0112]

[0113] (2.3) According to the coordination of the deformation of each layer of the thermal barrier coating and the turbine blade in the in-plane direction, the and Combined with the peak total strain of the surface nodes in the in-plane direction obtained in the first step Total valley strain The peak mechanical strains of the ceramic layer, thermally grown oxide layer, and bonding layer are calculated as follows: Valley mechanical strain

[0114] in,

[0115] represents the peak mechanical strain of layer i,

[0116] represents the valley mechanical strain of layer i,

[0117] represents the peak total strain of the matrix,

[0118] represents the total valley strain of the matrix,

[0119] represents the first thermal strain of layer i,

[0120] represents the second thermal strain of layer i,

[0121] represents the residual strain of layer i,

[0122] When the subscript i is 1, it represents a ceramic layer, when i is 2, it represents a thermally grown oxide layer, and when i is 3, it represents a bonding layer.

[0123] In the third step, the mechanically driven damage of the thermal barrier coating in the current cycle is calculated as follows:

[0124] (3.1) Using the peak mechanical strain of the bonding layer obtained in the second step Valley mechanical strain The mechanical strain range of the bonding layer in the in-plane direction is calculated as follows:

[0125] (3.2) Using the adhesive layer to generate mechanical strain range in the in-plane direction and the number of cycles N of the current cycle, and according to the strain fatigue damage equation of metal materials (the following formula), the mechanically driven damage D of the thermal barrier coating is calculated. cyc , where A and b are material constants:

[0126]

[0127] In the fourth step, the thickness of the thermally grown oxide layer for the current cycle is calculated as follows:

[0128] Using the peak temperature T of the surface node peak , the corresponding holding time t hold , the number of cycles N of the current cycle, and the thickness δ of the thermally grown oxide layer of the current cycle is calculated according to the oxidation kinetic equation of the growth of the thermally grown oxide layer (the following formula), where ΔH, T ref is the material constant, R is the uniform gas constant, n(T peak ) is the temperature-dependent material constant:

[0129]

[0130] In the fifth step, the oxidation-driven damage to the thermal barrier coating in the current cycle is calculated as follows:

[0131] Using the thickness of the thermally grown oxide layer δ obtained in the fourth step, the oxidation-driven damage D of the thermal barrier coating is calculated according to the oxidation damage equation (below): ox , where δ0 and m are material constants:

[0132]

[0133] In step 6, the total damage to the thermal barrier coating in the current cycle is calculated as follows:

[0134] Using the mechanically driven damage D obtained in the third step cyc and the oxidation-driven damage D obtained in step 5 ox According to the oxidation-mechanical nonlinear damage accumulation equation (the following formula), the total damage D is calculated N , where k is the material constant:

[0135] D N =D ox +D cyc -kD ox D cyc .

[0136] In the seventh step, the damage threshold of thermal barrier coating spalling is calculated as follows:

[0137] Using the second step As well as the thickness of the ceramic layer h, the Poisson's ratio ν1(T valley ), according to the quantitative characterization equation of thermal barrier coating interface damage (the following formula), the damage threshold D is calculated spall , where R0 is the material constant:

[0138]

[0139] In the eighth step, the thermal barrier coating spalling life is calculated as follows:

[0140] (8.1) Determine the total damage D obtained in step 6 N Whether the damage threshold D obtained in step 7 is reached spall ;

[0141] (8.2) If D N <D spall , the number of cycles becomes N+1, and the algorithm returns to step 3 for iterative calculation, and the calculation from step 3 to step 7 is repeated until the D at the surface node is N ≥D spall ;

[0142] (8.3) If D N ≥D spall , which means that the thermal barrier coating at the surface node has peeled off in the current cycle, and the peeling life is N. Output the surface node number, three-dimensional coordinates and corresponding peeling life. Then, determine whether all nodes have peeled off:

[0143] (8.3.1) If not, repeat steps 1 to 7 for the next node;

[0144] (8.3.2) If yes, the calculation process ends and the thermal barrier coating spalling life distribution of the turbine blade surface area is obtained.

[0145] Compared with the prior art, the present invention has the following advantages:

[0146] (1) The present invention uses the surface node information of the turbine blade without thermal barrier coating as input, and does not need to generate any additional thermal barrier coating geometric model or finite element mesh on the turbine blade surface, thereby realizing a rapid and accurate estimation of the spalling life of the thermal barrier coating for the turbine blade. It can be directly used as a post-processing of the existing turbine blade finite element analysis process, avoiding the cumbersome cross-scale modeling process of the "ceramic layer-thermal growth oxide layer-bonding layer-blade" system from micro to macro, and significantly reducing the workload of designers;

[0147] (2) The total damage of the thermal barrier coating used in the present invention is calculated by the oxidation-driven damage related to the thickness of the thermally grown oxide layer, the mechanical-driven damage related to the mechanical strain range of the bonding layer, and the coupling effect of the two. It can more accurately characterize the synergy and competition mechanism of various factors in the coating damage evolution process and has better adaptability to complex loads.

[0148] (3) The thermal barrier coating spalling damage threshold used in the present invention is calculated by the valley mechanical strain of the ceramic layer, which can more accurately reflect the effect of the load history on coating spalling.

[0149] Those skilled in the art should understand that the above embodiments are only for the purpose of clearly illustrating the present disclosure, and are not intended to limit the scope of the present disclosure. For those skilled in the art, other changes or modifications may be made based on the above disclosure, and these changes or modifications are still within the scope of the present disclosure.

Claims

1. A method for calculating the spalling life of thermal barrier coatings for turbine blades, characterized in that: The following steps are involved: Step 1: Acquire surface node information of a turbine blade without a thermal barrier coating, wherein the surface node information includes principal stress, principal strain, direction vector, peak temperature, valley temperature, and peak temperature holding time of the surface node; Step 2: Determine the peak total strain and the valley total strain of the surface node in the in-plane direction according to the principal stress, the principal strain and the direction vector; Step 3: Determine the peak mechanical strain and the valley mechanical strain of the ceramic layer, the thermally grown oxide layer and the bonding layer in the thermal barrier coating in the in-plane direction according to the peak total strain, the valley total strain, the peak temperature and the valley temperature; Step 4: determining the mechanically driven damage generated by the thermal barrier coating according to the peak mechanical strain and the valley mechanical strain of the bonding layer in the in-plane direction; Step 5: Calculating the oxidation-driven damage generated by the thermal barrier coating in the current cycle according to the peak temperature, the corresponding peak temperature holding time and the number of cycles in the current cycle; Step 6: Determine the total damage of the thermal barrier coating in the current cycle according to the mechanically driven damage and the oxidation driven damage; Step 7: determining a damage threshold of the thermal barrier coating for peeling off according to the valley mechanical strain of the ceramic layer in the in-plane direction; Step 8: If the total damage does not reach the damage threshold, the number of cycles of the current cycle is increased by 1, and steps 4 to 7 are repeated; if the total damage reaches the damage threshold, it is determined that the thermal barrier coating at the surface node has peeled off, and the corresponding surface node position and the number of cycles experienced are output, and steps 1 to 7 are repeated for the next surface node until it is determined that the thermal barrier coating at all surface nodes has peeled off, and the thermal barrier coating peeling life distribution of the turbine blade surface area is obtained; Determining the peak mechanical strain and the valley mechanical strain of the ceramic layer, the thermally grown oxide layer and the bonding layer in the thermal barrier coating in the in-plane direction according to the peak total strain, the valley total strain, the peak temperature and the valley temperature comprises: Calculate the first thermal strain of the ceramic layer, the thermally grown oxide layer and the bonding layer when the temperature changes from room temperature to the peak temperature and the second thermal strain when the temperature changes from room temperature to the valley temperature according to the peak temperature, the valley temperature and the thermal expansion coefficients of the ceramic layer, the thermally grown oxide layer and the bonding layer in the thermal barrier coating; Calculating the residual strain of the ceramic layer, the thermally grown oxide and the bonding layer when the stress-free initial temperature changes to room temperature according to the stress-free initial temperature of the thermal barrier coating and the thermal expansion coefficient of the turbine blade; Determine the peak mechanical strain and the valley mechanical strain of the ceramic layer, the thermally grown oxide and the bonding layer in the thermal barrier coating in the in-plane direction according to the peak total strain, the valley total strain, the first thermal strain, the second thermal strain and the residual strain; Determining the mechanically driven damage generated by the thermal barrier coating according to the peak mechanical strain and the valley mechanical strain of the bonding layer in the in-plane direction includes: Calculating the range of mechanical strain generated in the in-plane direction of the bonding layer according to the peak mechanical strain and the valley mechanical strain of the bonding layer in the in-plane direction; Calculating mechanically driven damage of the thermal barrier coating according to the range of mechanical strain generated by the bonding layer in the in-plane direction and the number of cycles of the current cycle; The calculating the mechanical strain range generated in the in-plane direction of the bonding layer according to the peak mechanical strain and the valley mechanical strain of the bonding layer in the in-plane direction comprises: The range of mechanical strain generated in the bonding layer in the in-plane direction of the thermal barrier coating is determined according to the following formula; in, It represents the range of mechanical strain generated in the bonding layer in the in-plane direction. represents the peak mechanical strain of the bonding layer, Indicates the valley mechanical stress of the bonding layer; The calculating of the mechanically driven damage of the thermal barrier coating according to the mechanical strain range generated by the bonding layer in the in-plane direction and the number of cycles of the current cycle comprises: The mechanically driven damage of thermal barrier coatings is determined according to the following formula; Among them, D cyc represents the mechanically driven damage of thermal barrier coatings, represents the range of mechanical strain produced by the bonding layer in the in-plane direction, A and b represent material constants, and N represents the number of cycles of the current cycle; The step of calculating the oxidation-driven damage caused by the thermal barrier coating in the current cycle according to the peak temperature, the corresponding peak temperature holding time and the number of cycles in the current cycle comprises: Calculating the thickness of the thermally grown oxide layer in the thermal barrier coating of the current cycle according to the peak temperature, the corresponding peak temperature holding time and the number of cycles of the current cycle; Calculating oxidation driven damage generated by the thermal barrier coating in the current cycle according to the thickness of the thermally grown oxide layer in the thermal barrier coating; The step of calculating the thickness of the thermally grown oxide layer in the thermal barrier coating of the current cycle according to the peak temperature, the corresponding peak temperature holding time and the number of cycles of the current cycle comprises: According to the following formula, the thickness of the thermally grown oxide layer in the thermal barrier coating of the current cycle is calculated; Where δ represents the thickness of the thermally grown oxide layer in the thermal barrier coating in the previous cycle, T peak represents the peak temperature, t hold represents the corresponding holding time, N represents the number of cycles of the current cycle, ΔH and T ref represents the material constant, R represents the unified gas constant, n(T peak ) is the temperature-dependent material constant; The step of calculating the oxidation-driven damage generated by the thermal barrier coating in the current cycle according to the thickness of the thermally grown oxide layer in the thermal barrier coating comprises: The oxidation-driven damage of the thermal barrier coating in the current cycle is calculated according to the following formula: D ox represents the oxidation-driven damage produced by the thermal barrier coating in the current cycle, δ represents the thickness of the thermally grown oxide layer in the thermal barrier coating in the previous cycle, and δ0 and m represent material constants; Determining the damage threshold of the thermal barrier coating for peeling off according to the valley mechanical strain of the ceramic layer in the in-plane direction includes: The damage threshold of thermal barrier coating spalling is calculated according to the following formula; Among them, D spall The damage threshold of thermal barrier coating peeling occurs. represents the valley mechanical strain of the ceramic layer in the in-plane direction, h represents the thickness of the ceramic layer, ν1(T valley ) represents the Poisson’s ratio of the ceramic layer in the in-plane direction at the valley temperature, and R0 represents the material constant.

2. The method for calculating the spalling life of thermal barrier coating for turbine blades according to claim 1, characterized in that: Determining the peak total strain and the valley total strain of the surface node in the in-plane direction according to the principal stress, the principal strain and the direction vector comprises: Determine the direction vector corresponding to the principal stress with the smallest absolute value as the surface normal vector; The two peak load principal strains and valley load principal strain components whose direction vectors are inconsistent with the surface normal vector are taken as the total in-plane strains of the surface nodes; Among the principal strains at the peak load, the larger value of the total in-plane strain of the surface node is taken as the peak total strain of the node in the in-plane direction; In the valley load principal strain, the larger value of the in-plane total strain of the surface node is taken as the valley total strain of the node in the in-plane direction.

3. The method for calculating the spalling life of thermal barrier coating for turbine blades according to claim 1, characterized in that: The step of calculating the first thermal strain of the ceramic layer, the thermally grown oxide layer, and the bonding layer when the temperature changes from room temperature to the peak temperature and the second thermal strain when the temperature changes from room temperature to the valley temperature according to the peak temperature, the valley temperature, and the thermal expansion coefficients of the ceramic layer, the thermally grown oxide, and the bonding layer in the thermal barrier coating comprises: Calculate the first thermal strain of the ceramic layer, the thermally grown oxide and the bonding layer when the temperature changes from room temperature to the peak temperature and the second thermal strain when the temperature changes from room temperature to the valley temperature according to the following formula; in, represents the first thermal strain of layer i, α i (T) represents the thermal expansion coefficient of layer i, T peak represents the peak temperature, T0 represents the room temperature, represents the second thermal strain of layer i, T valley represents the valley temperature. When the subscript i is 1, it represents the ceramic layer; when i is 2, it represents the thermally grown oxide layer; when i is 3, it represents the bonding layer.

4. The method for calculating the spalling life of thermal barrier coating for turbine blades according to claim 1, characterized in that: The method of calculating the residual strain of the ceramic layer, the thermally grown oxide layer and the bonding layer when the stress-free initial temperature of the thermal barrier coating changes to room temperature according to the stress-free initial temperature of the thermal barrier coating and the thermal expansion coefficient of the turbine blade comprises: Calculate the residual strain of the ceramic layer, the thermally grown oxide layer and the bonding layer when the stress-free initial temperature changes to room temperature according to the following formula; represents the residual strain of layer i when it changes from the stress-free initial temperature to room temperature, α s (T) represents the thermal expansion coefficient of the turbine blade, α i (T) represents the thermal expansion coefficient of layer i, T free represents the stress-free initial temperature of the thermal barrier coating, T0 represents room temperature, the subscript i is 1 for the ceramic layer, i is 2 for the thermally grown oxide layer, and i is 3 for the bonding layer.

5. The method for calculating the spalling life of thermal barrier coating for turbine blades according to claim 1, characterized in that: Determining the peak mechanical strain and the valley mechanical strain of the ceramic layer, the thermally grown oxide, and the bonding layer in the thermal barrier coating in the in-plane direction according to the peak total strain, the valley total strain, the first thermal strain, the second thermal strain, and the residual strain comprises: The peak mechanical strain and valley mechanical strain of the ceramic layer, the thermally grown oxide layer and the bonding layer in the thermal barrier coating in the in-plane direction are determined according to the following formulas; in, represents the peak mechanical strain of layer i, represents the valley mechanical strain of layer i, represents the peak total strain of the matrix, represents the total valley strain of the matrix, represents the first thermal strain of layer i, represents the second thermal strain of layer i, represents the residual strain of layer i, When the subscript i is 1, it represents a ceramic layer, when i is 2, it represents a thermally grown oxide layer, and when i is 3, it represents a bonding layer.

6. The method for calculating the spalling life of thermal barrier coating for turbine blades according to claim 1, characterized in that: Determining the total damage of the thermal barrier coating in the current cycle according to the mechanically driven damage and the oxidation driven damage includes: The total damage of the thermal barrier coating in the current cycle is calculated according to the following formula: D N =D ox +D cyc -kD ox D cyc ; Among them, D N It represents the total damage of thermal barrier coating in the current cycle, D cyc represents the mechanically driven damage of thermal barrier coating, D ox represents the oxidation-driven damage caused by the thermal barrier coating in the current cycle, and k represents the material constant.

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