A method for improving simulation precision of a knuckle arm bearing capacity

Abstract

The present application belongs to the technical field of chassis knuckle steering rod arm bearing capacity simulation, and particularly relates to a method for improving the simulation precision of knuckle arm bearing capacity; firstly, the material nonlinearity of the knuckle, ball head and inner sleeve is considered, the interference contact between the inner sleeve and the knuckle is considered, the contact between the ball head pin and the inner sleeve is considered, the initial pre-tightening force of the ball head pin is considered, the load is applied along the direction of the pull rod at the outer ball head of the steering pull rod, the load displacement curve of the loading point is calculated, with the increase of the load, the structure gradually yields, the slope of the bearing capacity curve gradually becomes smaller, when the slope reaches a certain value, it is determined that the entire structure yields, i.e. loses the bearing capacity, the present application is based on the finite element model of the knuckle and ball head assembly, and the load displacement curve method is used to calculate and evaluate the bearing capacity of the structure, this method is not the local behavior of the structure, but the overall behavior of the structure, thereby improving the simulation precision of the knuckle steering pull rod arm bearing capacity.

Description

Technical Field

[0001] This invention belongs to the field of chassis steering knuckle tie rod arm load-bearing capacity simulation technology, specifically involving a method to improve the simulation accuracy of steering knuckle arm load-bearing capacity. Background Technology

[0002] The steering tie rod arm of the chassis steering knuckle should meet certain load-bearing capacity requirements. The traditional development method is as follows: Based on the multibody dynamics load decomposition of the whole vehicle, the load F at the steering tie rod under the curb impact condition is obtained. On this load F, 5KN is added to ensure that the buckling load of the steering tie rod is greater than (F+5KN). That is, when the whole vehicle is subjected to a curb impact condition, the steering tie rod is guaranteed not to buckle. A load of F+10KN is applied at the ball joint of the steering knuckle tie rod arm along the direction of the steering tie rod. The equivalent plastic strain at the steering knuckle arm is evaluated. If the equivalent plastic strain is less than 50% of the elongation of the steering knuckle material, the load-bearing capacity of the steering knuckle arm is determined to be greater than F+10KN. That is, the load corresponding to the equivalent plastic strain at a certain point of the steering knuckle arm reaching 50% of the material elongation is the load-bearing capacity of the steering knuckle tie rod arm. However, the load-bearing capacity calculation and evaluation method based on the local equivalent plastic strain of the structure is not accurate enough because: 1. During modeling and simulation, the ball joint pin contacts the steering knuckle arm. Due to the algorithm itself, there is a singular region in the equivalent plastic strain of the contact area, and the calculated result is larger than the actual result. When the equivalent plastic strain in this area reaches 50% of the material elongation, the corresponding applied tie rod load is often too small, that is, the load-bearing capacity is too small; 2. Even if a certain point in the structure reaches 50% of the material plastic strain, the surrounding structure of this point still has the load-bearing capacity, that is, the yielding at a certain point does not represent the yielding of the entire structure.

[0003] In summary, when using the equivalent plastic strain method to evaluate the load-bearing capacity of the steering knuckle tie rod arm, the calculated structural load-bearing capacity is underestimated, resulting in structural redundancy and hindering lightweight design. Summary of the Invention

[0004] To overcome the above problems, this invention provides a method to improve the simulation accuracy of the load-bearing capacity of the steering knuckle arm. Based on the finite element model of the steering knuckle and ball joint assembly, the load-displacement curve method is used to calculate and evaluate the structural load-bearing capacity. This method does not reflect the local behavior of the structure, but rather the overall behavior of the structure, thereby improving the simulation accuracy of the load-bearing capacity of the steering knuckle tie rod arm.

[0005] A method for improving the simulation accuracy of the load-bearing capacity of a steering knuckle arm includes the following:

[0006] Step 1: Based on the three-dimensional models of steering knuckle 1, ball head bolt 3, inner sleeve 5 and ball head nut 4, the software is used to divide each three-dimensional model into finite element meshes. The steering knuckle uses second-order tetrahedral elements, the ball head bolt 3 uses second-order tetrahedral elements, and the inner sleeve 5 and ball head nut 4 use first-order hexahedral elements. The structural material and cross-sectional properties are then assigned.

[0007] Step 2: Establish the interference fit between the steering knuckle 1 and the inner sleeve 5; establish the contact relationship between the ball head bolt 3 and the inner sleeve 5; establish the binding relationship between the ball head nut 4 and the ball head bolt 3; and establish the contact relationship between the ball head nut 4 and the steering knuckle 1.

[0008] Step 3: Simulation loading is performed in three loading processes: such as... Figure 2 As shown;

[0009] A. The first load step in the simulation is the interference fit between the inner sleeve 5 and the steering knuckle 1. The displacement of the load application point at this time is recorded, and the displacement components in the three directions of the load application point are solved, denoted as x1 and x2 respectively. 过盈配合 x2 过盈配合 and x3 过盈配合 ;

[0010] B. The second load step in the simulation is to apply a preload at ball-end nut 4 and record the displacement of the load application point. Solve for the displacement components in the three directions of the load application point, denoted as x1. 螺栓预紧 x2 螺栓预紧 and x3 螺栓预紧 ;

[0011] C. The third load step in the simulation loading is to divide the total load to be applied into incremental steps along the tie rod direction at the ball joint bolt 3 where the outer point 7 of the steering tie rod is located, and apply the load in multiple increments along the tie rod direction with the same load increment until a load of 100,000 N is applied. The displacement of the load application point is recorded each time the load is increased, and the displacement components x1 in the three directions of the load application point are solved for each load increase. 施加 x2 施加 and x3 施加 ;

[0012] Step four, correct the displacement components in the three directions of the load application point obtained in step three (C):

[0013] Each time the load is increased, the corrected displacement components y1, y2, and y3 of the load application point in the three directions are calculated according to the following formulas:

[0014] y1=x1 施加 -x1 螺栓预紧

[0015] y2=x2 施加 -x2螺栓预紧

[0016] y3=x3 施加 -x3 螺栓预紧 ;

[0017] Step 5: Take the square root of the sum of the squares of the corrected displacement components y1, y2, and y3 at the load application point in the three directions to obtain the corrected resultant displacement y at the load application point. 合 ;

[0018] Plot a load-displacement curve with the corrected resultant displacement at the load application point as the abscissa and the magnitude of the applied load as the ordinate.

[0019] Step 6: When the rate of change of the slope of the load-displacement curve drops to 50% for the first time, it is considered that the structure as a whole has yielded. The magnitude of the applied load at this time is the load-bearing capacity of the steering knuckle tie rod arm.

[0020] Step one involves using Hypermesh finite element software to generate finite element meshes for each 3D model.

[0021] Step three involves using ABAQUS software to solve for the displacement components in the three directions of the load application point.

[0022] Both steps four and five utilize EXCEL software for data recording and processing, and for plotting load-displacement curves.

[0023] The slope change rate of the load displacement curve in step six is ​​the percentage of the curve's slope to the initial slope. Specifically, it is calculated as the slope of the curve when the load is applied at the next stage divided by the initial curve slope.

[0024] In step six, the initial slope of the load-displacement curve is the resultant displacement after the load increment is divided by the corrected displacement of the load application point when the load is first applied in step three (C).

[0025] In step six, the slope of the load-displacement curve is the load increment divided by the difference in corrected displacement between two increment steps.

[0026] In step C of step three, the load direction of the progressively applied load is set to the ball joint bolt 3 where the outer point 7 of the steering tie rod is located, pointing outward along the tie rod direction. The magnitude of the applied load corresponding to the overall structure yielding is the bearing capacity of the steering tie rod arm of the steering knuckle in that direction.

[0027] In step C of step three, the load direction of the progressively applied load is set to the ball joint bolt 3 where the outer point 7 of the steering tie rod is located, pointing inward along the tie rod direction. The magnitude of the applied load corresponding to the overall structure yielding is the load-bearing capacity of the steering tie rod arm in that direction.

[0028] Compared with the prior art, the beneficial effects of the present invention are as follows:

[0029] This invention employs a load-displacement curve calculation and evaluation method to improve the simulation accuracy of the steering knuckle arm's load-bearing capacity. Its advantages lie in first considering the material nonlinearity of the steering knuckle, ball joint, and inner sleeve; considering the interference contact between the inner sleeve and the steering knuckle; considering the contact between the ball joint pin and the inner sleeve; and considering the initial preload of the ball joint pin. A load is applied along the tie rod direction at the outer ball joint of the steering tie rod, and the load-displacement curve at the loading point is calculated. As the load increases, the structure gradually yields, and the slope of the load-bearing capacity curve gradually decreases. When the slope reaches a certain value, it is determined that the entire structure has yielded, i.e., lost its load-bearing capacity. This method evaluates the overall behavior of the structure, not its local behavior, thus better reflecting the structure's true load-bearing capacity and improving simulation accuracy. Attached Figure Description

[0030] To more clearly illustrate the technical solutions in the embodiments of the present invention, the accompanying drawings used in the description of the embodiments of the present invention will be briefly introduced below. Obviously, the accompanying drawings described below are only some embodiments of the present invention. For those skilled in the art, other drawings can be obtained based on the content of the embodiments of the present invention and these drawings without creative effort.

[0031] Figure 1 This is a schematic diagram of a three-dimensional model of the steering knuckle assembly of the present invention.

[0032] Figure 2 Simulation data for the load-bearing capacity of the steering knuckle tie rod arm.

[0033] Figure 3 This is the load-bearing capacity curve of the steering knuckle tie rod arm.

[0034] The components are: 1. Steering knuckle; 2. Wheel center; 3. Ball head bolt; 4. Ball head nut; 5. Inner sleeve; 6. Outer point of upper control arm; 7. Outer point of steering tie rod; 8. Outer point of front lower control arm; 9. Outer point of rear lower control arm. Detailed Implementation

[0035] The present invention will now be described in further detail with reference to the accompanying drawings and embodiments. It should be understood that the specific embodiments described herein are merely illustrative of the invention and not intended to limit it. Furthermore, it should be noted that, for ease of description, the accompanying drawings show only the parts relevant to the present invention, and not all of the structures.

[0036] In the description of this invention, unless otherwise explicitly specified and limited, the terms "connected," "linked," and "fixed" should be interpreted broadly. For example, they can refer to a fixed connection, a detachable connection, or an integral part; they can refer to a mechanical connection or an electrical connection; they can refer to a direct connection or an indirect connection through an intermediate medium; they can refer to the internal communication of two components or the interaction between two components. Those skilled in the art can understand the specific meaning of the above terms in this invention based on the specific circumstances.

[0037] In this invention, unless otherwise explicitly specified and limited, "above" or "below" the second feature can include direct contact between the first and second features, or contact between the first and second features through another feature between them. Furthermore, "above," "over," and "on top" of the second feature includes the first feature directly above or diagonally above the second feature, or simply indicates that the first feature is at a higher horizontal level than the second feature. "Below," "below," and "under" the second feature includes the first feature directly below or diagonally below the second feature, or simply indicates that the first feature is at a lower horizontal level than the second feature.

[0038] In the description of this embodiment, the terms "upper," "lower," "left," and "right," etc., refer to the orientation or positional relationship shown in the accompanying drawings. They are used only for ease of description and simplification of operation, and do not indicate or imply that the device or element referred to must have a specific orientation, or be constructed and operated in a specific orientation. Therefore, they should not be construed as limitations on the present invention. In addition, the terms "first" and "second" are used only for distinction in description and have no special meaning.

[0039] Example 1

[0040] A method for improving the simulation accuracy of the load-bearing capacity of a steering knuckle arm includes the following:

[0041] Step 1, as follows Figure 1 As shown, based on the three-dimensional models of steering knuckle 1, ball head bolt 3, inner sleeve 5 and ball head nut 4 provided by the design department, the software is used to divide each three-dimensional model into finite element meshes. The steering knuckle uses second-order tetrahedral elements, the ball head bolt 3 uses second-order tetrahedral elements, and the inner sleeve 5 and ball head nut 4 all use first-order hexahedral elements. Structural material and cross-sectional properties are also assigned.

[0042] The steering knuckle 1 is provided with three ball head bolts 3. Each ball head bolt 3 is fixed inside the steering knuckle 1 by an inner sleeve 5. The heads of the three ball head bolts 3 serve as the outer point 7 of the steering tie rod, the outer point 8 of the front lower control arm, and the outer point 9 of the rear lower control arm, respectively.

[0043] Step 2: Establish the interference fit between the steering knuckle 1 and the inner sleeve 5; establish the contact relationship between the ball head bolt 3 and the inner sleeve 5; establish the binding relationship between the ball head nut 4 and the ball head bolt 3; and establish the contact relationship between the ball head nut 4 and the steering knuckle 1.

[0044] Step 3: Simulation loading is performed in three loading processes: such as... Figure 2 As shown;

[0045] A. The first load step in the simulation is the interference fit between the inner sleeve 5 and the steering knuckle 1. The displacement of the load application point at this time is recorded in an Excel spreadsheet. The ABAQUS software is then used to calculate the displacement components in the three directions of the load application point at this time, denoted as x1. 过盈配合 x2 过盈配合 and x3 过盈配合 ;

[0046] B. The second load step in the simulation is to apply a preload at the ball-end nut 4, and record the displacement of the load application point at this time in the form of an EXCEL table. Submit the ABAQUS software to calculate the displacement components of the load application point in three directions at this time, denoted as x1. 螺栓预紧 x2 螺栓预紧 and x3 螺栓预紧 The displacement components in step B are obtained based on step A.

[0047] C. The third load step in the simulation loading is to divide the total load to be applied into incremental steps along the tie rod direction at the ball joint bolt 3, where the outer point 7 of the steering tie rod is located, and apply the load in multiple increments until a load of 100,000 N is applied. The displacement of the load application point at each load increase is recorded in an EXCEL table, and the displacement components x1 in the three directions of the load application point at each load increase are solved. 施加 x2 施加 and x3 施加 ;

[0048] Step four, correct the displacement components in the three directions of the load application point obtained in step three (C):

[0049] Each time the load is increased, the corrected displacement components y1, y2, and y3 of the load application point in the three directions are calculated according to the following formulas:

[0050] y1=x1 施加 -x1 螺栓预紧

[0051] y2=x2 施加 -x2 螺栓预紧

[0052] y3=x3 施加 -x3螺栓预紧 ;

[0053] Step 5: Take the square root of the sum of the squares of the corrected displacement components y1, y2, and y3 at the load application point in the three directions to obtain the corrected resultant displacement y at the load application point. 合 ;

[0054] Plot a load-displacement curve with the corrected resultant displacement at the load application point as the abscissa and the magnitude of the applied load as the ordinate.

[0055] Step 6: When the rate of change of the slope of the load-displacement curve drops to 50% for the first time, it is considered that the structure as a whole has yielded. The magnitude of the applied load at this time is the load-bearing capacity of the steering knuckle tie rod arm.

[0056] Step one involves using Hypermesh finite element software to generate finite element meshes for each 3D model.

[0057] Step three involves using ABAQUS software to solve for the displacement components in the three directions of the load application point.

[0058] Both steps four and five utilize EXCEL software for data recording and processing, and for plotting load-displacement curves.

[0059] In step six, the slope change rate of the load-displacement curve is the percentage of the curve's slope relative to the initial slope. Specifically, it is calculated as: the slope of the curve when the load is applied at the next stage divided by the initial slope. 1 / (0.18079-0.089847) = 10.9959.

[0060] In step six, the initial slope of the load-displacement curve is the load increment of 1 kN divided by the corrected net displacement of the load application point when the load is first applied in step three (C). 11.12999 is the initial slope, where 11.12999 = 1 / 0.089847 (corrected net displacement).

[0061] In step six, the slope of the load-displacement curve is the load increment = 1 kN divided by the difference in corrected displacement between two increment steps.

[0062] In actual calculations of the steering knuckle arm's load-bearing capacity, calculations must be performed in both directions. First, using this method, apply a load of 100,000 N over time, always moving from the outer point to the inner point, and plot the load-bearing capacity curve. Then, using the same method, apply a load of 100,000 N over time, always moving from the inner point to the outer point, and plot the load-bearing capacity curve again.

[0063] In step C of step three, the load direction of the progressively applied load is set to the ball joint bolt 3 where the outer point 7 of the steering tie rod is located, pointing outward along the tie rod direction. The magnitude of the applied load corresponding to the overall structure yielding is the bearing capacity of the steering tie rod arm of the steering knuckle in that direction.

[0064] In step C of step three, the load direction of the progressively applied load is set to the ball joint bolt 3 where the outer point 7 of the steering tie rod is located, pointing inward along the tie rod direction. The magnitude of the applied load corresponding to the overall structure yielding is the load-bearing capacity of the steering tie rod arm in that direction.

[0065] The method of this invention evaluates the structural bearing capacity based on the load-displacement curve method at the loading point, which evaluates the overall behavior rather than the local behavior, thereby improving the simulation accuracy.

[0066] The initial slope of the curve is normalized to 1, and the structure is judged to have lost its load-bearing capacity when the relative change of the curve slope reaches a certain index.

[0067] During Excel data processing, it is necessary to subtract the initial displacement of the tie rod outer point generated by the first two (or several) load steps, and the displacement components should be subtracted separately to ensure the accuracy of the displacement.

[0068] The applied load needs to be applied incrementally, and the displacement of the loading point needs to be output step by step.

[0069] Example 2

[0070] This section uses the front steering knuckle of a certain vehicle model as an example to detail the steps for improving the simulation accuracy of steering knuckle arm load capacity using the load capacity curve method.

[0071] The first step is to use the three-dimensional geometric models of the steering knuckle 1, ball joint bolt 3, ball joint nut 4, and inner sleeve 5 provided by the design department, such as... Figure 1 As shown. Based on the Hypermesh preprocessing finite element software, geometric processing was performed, and finite element meshes were generated. The steering knuckle was a second-order tetrahedron, the ball head bolt 3 was a second-order tetrahedron, and the ball head nut 4 and inner sleeve 5 were first-order hexahedrons. The structural material and section properties were also assigned.

[0072] The second step is to establish the interference fit between the steering knuckle 1 and the inner sleeve 5, the contact relationship between the ball head bolt 3 and the inner sleeve 5, the binding relationship between the ball head nut 4 and the ball head bolt 3, and the contact relationship between the ball head nut 4 and the steering knuckle 1, taking into account material nonlinearity.

[0073] The third step, the loading process is divided into 3 load steps. First, the interference fit between the inner sleeve 5 and the steering knuckle 1. Second, the bolt preload is applied at the ball head nut 4. Finally, the load is gradually applied along the direction of the tie rod at the ball head pin bolt 3 where the outer point 7 of the steering tie rod is located, until a load of 100,000N is applied. In this embodiment, the load direction is along the tie rod direction pointing outward. In the actual calculation process, it is also necessary to calculate the direction along the tie rod direction pointing inward. Since the subsequent post-processing method and the method of drawing the load displacement curve are the same, only the example of loading outward along the tie rod is given.

[0074] Step 4: Set the load increment in the tie rod direction to 0.01, which is equivalent to a 100,000 N load. Initially apply 1,000 N, with an increment of 1,000 N. After each load application, output the displacement data of the loading point in an Excel spreadsheet. Submit the data to the ABAQUS software for calculation. (The rest of the text appears to be unrelated and possibly machine-generated.) Figure 3 As shown: After the two load steps of interference fit and bolt preload are calculated, the displacements of the loading point, i.e., the outer points of the tie rod, in the three directions x1, x2, and x3 are -0.0093mm, 0.0175mm, and 0.1688mm, respectively. After applying a 1000N load along the tie rod direction, the displacements of the outer points of the tie rod in the three directions x1, x2, and x3 are 0.01365mm, 0.1042mm, and 0.1740mm, respectively. However, the actual displacement caused by applying a 1000N load along the tie rod direction should be [0.01365-(-0.0093)]mm, (0.1042-0.0175)mm, and (0.1740-0.1688)mm. The corrected displacement components are shown in […]. Figure 3 The corrected resultant displacement (i.e., the square root of the sum of the squares of the displacement components in the three directions) in columns y1, y2, and y3 is as follows: Figure 2 As shown.

[0075] Fifth, using the applied load column and the corrected resultant displacement column, plot the load-displacement curve at the loading point, i.e., the outer point of the tie rod, as shown below. Figure 3 As shown in the load-displacement curve, it can be seen that as the load increases, the displacement increment at the loading point becomes larger and larger, indicating that the overall structure of the steering knuckle arm gradually loses its load-bearing capacity and the overall structure yields, rather than a local point.

[0076] Step 6: Figure 2 In this process, the slope of the load-displacement curve is obtained by dividing the load increment of 1 kN by the displacement difference between two increment steps. For example, the slope of the first load increment step is 11.12999. This slope is then normalized to 1, and the slope of subsequent curves is divided by 11.12999 to obtain the slope change relative to the initial state. When the slope change is 50%, the structure is considered to have lost its overall load-bearing capacity. At this time, the corresponding load on the tie rod's external point is 50 kN. Figure 3 As shown.

[0077] The preferred embodiments of the present invention have been described in detail above with reference to the accompanying drawings. However, the scope of protection of the present invention is not limited to the specific details in the above embodiments. Within the scope of the technical concept of the present invention, any person skilled in the art can make equivalent substitutions or changes based on the technical solution and inventive concept of the present invention within the scope of the technology disclosed in the present invention. These simple modifications are all within the scope of protection of the present invention.

[0078] It should also be noted that the various specific technical features described in the above specific embodiments can be combined in any suitable manner without contradiction. In order to avoid unnecessary repetition, the present invention will not describe the various possible combinations separately.

[0079] Furthermore, various different embodiments of the present invention can be combined in any way, as long as they do not violate the spirit of the present invention, they should also be regarded as the content disclosed by the present invention.

Claims

1. A method for improving simulation accuracy of a knuckle arm load carrying capacity, characterized by The method comprises the following steps: Step one, based on the three-dimensional model of the knuckle (1), ball pin bolt (3), inner sleeve (5) and ball nut (4), the software is used to divide the finite element grid for each three-dimensional model, the knuckle is used with the second order tetrahedral element, the ball pin bolt (3) is used with the second order tetrahedral element, the inner sleeve (5) and the ball nut (4) are used with the first order hexahedral element, and the structural material and the cross-section attribute are given; Step two, the interference fit relationship between the knuckle (1) and the inner sleeve (5) is established, the contact relationship between the ball pin bolt (3) and the inner sleeve (5) is established, the binding relationship between the ball nut (4) and the ball pin bolt (3) is established, and the contact relationship between the ball nut (4) and the knuckle (1) is established; Step three, the simulation loading is carried out in three loading processes; A. The first load step of the simulation is the interference fit between the inner sleeve (5) and the knuckle (1), and the displacement of the load point at this time is recorded. The displacement components of the load point in three directions are solved, respectively denoted as x1 过盈配合 , x2 过盈配合 and x3 过盈配合 ; B. The second load step in the simulation is to apply the preload force at the ball nut (4), and record the displacement of the load application point, solve the displacement components of the load application point in three directions, respectively denoted as x1 螺栓预紧 , x2 螺栓预紧 and x3 螺栓预紧 ; C. The third load step in the simulation is to load the total load to be loaded in increments along the pull rod direction at the ball stud bolt (3) where the outer point 7 of the steering pull rod is located, and the total load is divided into incremental steps, until a load of 100000N is applied, and the displacement of the load point is recorded at each incremental load, and the displacement components x1 施加 , x2 施加 , and x3 施加 in three directions of the load point at each incremental load are solved. Step four, the displacement components of the load point in three directions obtained in step three are corrected; When the load is increased each time, the corrected displacement components y1, y2 and y3 of the load point in three directions are calculated according to the following formula respectively: y1=x1 施加 -x1 螺栓预紧 y2=x2 施加 -x2 螺栓预紧 y3=x3 施加 -x3 螺栓预紧 ; Step five, square and root of the square sum of the three direction corrected displacement components y1, y2 and y3 of the load application point to obtain the corrected resultant displacement y of the load application point 合 ; The corrected displacement of the load point is taken as the horizontal coordinate, and the applied load size is taken as the vertical coordinate to draw the load displacement curve diagram; Step six, when the slope change rate of the curve in the load displacement curve diagram is reduced to 50% for the first time, it is considered that the overall structure is yielded, and the corresponding applied load size is the bearing capacity of the knuckle steering pull rod arm; The step one is to divide the finite element grid for each three-dimensional model by using the Hypermesh finite element software; The step three is to solve the displacement components of the load point in three directions by using the ABAQUS software; The steps four and five are to record and process the data by using the EXCEL software, and draw the load displacement curve diagram; In the step six, the slope change rate of the curve in the load displacement curve diagram is the percentage of the slope of the curve to the initial slope, and the specific calculation method is that the curve slope at the next level of applied load is divided by the initial curve slope; In the step six, the initial slope of the curve in the load displacement curve diagram is the load increment divided by the corrected displacement of the load point when the load is applied for the first time in step three C; In the step six, the slope of the load displacement curve diagram is the load increment divided by the difference between the corrected displacements between two incremental steps; In the step three C, the load direction of the gradually multiple loads is set as the direction of the ball pin bolt (3) where the outer point (7) of the steering pull rod is located and points to the inner point along the pull rod direction, and the corresponding applied load size when the overall structure is yielded finally is the bearing capacity of the knuckle steering pull rod arm in the direction. In the step three C, the load direction of the gradually multiple loads is set as the direction of the ball pin bolt (3) where the outer point (7) of the steering pull rod is located and points to the inner point along the pull rod direction, and the corresponding applied load size when the overall structure is yielded finally is the bearing capacity of the knuckle steering pull rod arm in the direction.

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