TWI505955B - Evaluation method for panel - Google Patents

Description

Panel evaluation method

The present invention relates to a panel evaluation method for evaluating the stretch rigidity of a panel member having a convex shape on one side as a whole of a panel member for an automobile.

One of the characteristics required for a panel component (a door, a hood, a roof, etc.) for an automobile is tensile rigidity. Previously, the tensile rigidity was obtained by an experiment using a measuring instrument that actually measured the tensile rigidity, or was obtained by a model analysis method to calculate the tensile rigidity.

In order to improve the above-described tensile rigidity, it is an effective method to optimize the shape of the part of the panel. In particular, the curvature of the panel has a large effect on the tensile stiffness.

On the other hand, Patent Document 1 describes that the design of the maximum curvature and the minimum curvature at an arbitrary position on the panel is fixed so that the tensile rigidity on the panel is fixed.

Further, Patent Document 2 describes a method of calculating the stretching from the product of the radius of curvature of the vehicle body in the left-right direction at the center of the sunroof panel and the radius of curvature of the vehicle body in the front-rear direction, the Young's Modulus, and the thickness of the panel. rigidity.

Prior technical literature Patent literature

Patent Document 1: Japanese Patent No. 3229399

Patent Document 2: Japanese Patent Laid-Open Publication No. 2004-17682

In the embodiment of Patent Document 1, when a load of 5 kgf is applied The displacement is used to adjust the tensile stiffness. However, even under the condition that the sum of the maximum curvature and the minimum curvature is fixed, the path of the load-displacement curve until the load reaches 5 kgf is also different. Therefore, as described in Patent Document 1, it is not necessarily said that the tensile rigidity is equal if the sum of the maximum curvature and the minimum curvature is equal.

On the other hand, according to the formula described in Patent Document 2, it can be understood that the tensile rigidity is equal if the curvature radius of the vehicle body in the front-rear direction is equal to the product of the curvature radius in the left-right direction of the vehicle body. However, in the same manner as in the case of Patent Document 1, since the path of the load-displacement curve is different under the condition that the radius of curvature of the vehicle body in the front-rear direction and the radius of curvature of the vehicle body in the left-right direction are different, it is not necessarily said that even The product of the curvature radius in the front-rear direction of the vehicle body is equal to the product of the curvature radius in the left-right direction of the vehicle body, and the tensile rigidity is also equal.

For example, as shown in FIG. 11, even if the displacement β at the time of reaching a certain load α is equal, if the path of the "load-displacement" until the curve A or the curve B is different, the touch feeling when the panel is actually pressed is completely different, so that the pull is completely different. The stiffness is not equal. In other words, if the load-displacement relationship of the portion to which the load is applied at each position of the panel cannot be obtained with high precision, the tensile rigidity of the panel member cannot be evaluated with a predetermined accuracy.

The present invention has been made in view of the above aspects, and an object thereof is to evaluate the tensile rigidity of a panel member easily and with higher precision.

Here, what is obtained by using the formula described in Patent Document 2 is only the first slope when the load is applied at the start of the load-displacement curve. Stretch-rigid load-displacement curves are usually shown as upwardly convex shapes, along with When the shift is increased, the deviation between the value obtained by the formula described in Patent Document 2 and the actual tensile rigidity value is increased. In particular, the required tensile rigidity varies depending on the part or part of the evaluation object, so that only the initial slope of the load-displacement curve is obtained, which is insufficient for the evaluation of the tensile rigidity.

In this regard, the inventors obtained the following findings: the ratio of the radius of curvature of the minimum curvature of the evaluation position to the radius of curvature of the radius of curvature orthogonal to the minimum curvature, that is, the curvature ratio, and the load-displacement curve The path is different. In addition, in many cases, the direction orthogonal to the minimum curvature is the direction of the maximum curvature. That is, the inventors and the like have found through the investigation of the tensile rigidity of the panels of various shapes that the ratio of the minimum curvature direction on the panel and the two curvatures in the direction orthogonal to the minimum curvature direction, and The combination of the plate thicknesses enables a more accurate calculation of the load-displacement curve when a load is applied to the panel.

The present invention has been completed based on the following findings, and the gist thereof is as follows.

(1) A panel evaluation method for evaluating the tensile rigidity of a panel member having a convex shape on one side as a whole, and is characterized in that the maximum radius of curvature of the panel member set at the evaluation position of the panel member is obtained. a first radius of curvature and a second radius of curvature which is a radius of curvature of a direction orthogonal to a curvature direction of the maximum radius of curvature, and a ratio of the obtained first radius of curvature to the second radius of curvature is obtained The plate thickness of the panel component at the evaluation position is obtained by the curvature ratio, and the load-displacement characteristic at the evaluation position is obtained using the obtained curvature ratio and the plate thickness.

(2) The panel evaluation method according to the above (1), wherein the curvature ratio and the plate thickness are obtained by using the curvature ratio and the displacement as the quadratic function of the variable. The above load-displacement characteristics.

(3) A panel evaluation method for determining a reinforcement position by evaluating a plurality of evaluation positions by the panel evaluation method as described in (1) or (2) above.

According to the present invention, the tensile rigidity of the panel can be easily evaluated.

Next, an embodiment of the present invention will be described using the drawings.

(assess target)

In the present embodiment, a sunroof panel (hereinafter simply referred to as a panel) which is a panel member for an automobile is evaluated as a panel member having a convex shape on one side as a whole. The evaluation object may be a door panel or a panel part other than the automobile panel part. As long as the panel member having a convex shape on one side as a whole, that is, even if a part has a concave curvature, it can be applied as long as the overall contour shape is formed by the convex curvature. In addition, it is assumed that a load is applied from the convex side.

Further, it is assumed that a reinforcing member such as a reinforcement or a rib is not provided in the panel evaluated by the following method. Alternatively, even if the reinforcing member is provided, the position where the influence of the reinforcing member is low is set as the evaluation position.

(panel design method)

Fig. 1 is a view showing the use of the tensile rigidity evaluation method of the present embodiment. A schematic flow chart of the sequence of panel design methods.

First, in step S10, the shape of the panel to be evaluated is initially set, and the model of the panel is determined. Regarding the panel shape, specifically, the radius of curvature and the thickness of the panel are set. Here, the radius of curvature of the panel need not be the same on the panel, and may also have a distribution.

Then, in step S20, a plurality of evaluation positions H are set on the panel 1 to be evaluated as described above.

Then, in step S30, the following values of the radius of curvature and the thickness of the plate are obtained for each of the plurality of evaluation positions set in step S20.

Regarding each evaluation position, the direction of the minimum curvature is obtained, and the maximum radius of curvature of the radius of curvature of the minimum curvature is obtained, and the radius of curvature is set as the first radius of curvature. Further, a radius of curvature in a direction orthogonal to the direction of the minimum curvature is obtained, and the obtained radius of curvature is set as the second radius of curvature. Then, the plate thickness at each evaluation position is obtained.

Here, each of the curvature radii may be calculated based on the shape information of the panel shape which is initially set, and may be calculated by using a software such as spreadsheet software, or may be obtained by actual measurement.

When measuring, the radius of curvature can be measured by using a 3-point pressure gauge, a device using a three-dimensional shape measuring instrument, or the like. The thickness of the sheet can be determined by a device such as a micrometer or a thickness meter.

Then, in step S40, the curvature ratio at each evaluation position is obtained based on the first curvature radius and the second curvature radius obtained as described above based on the following equation.

Curvature ratio = (2nd radius of curvature / 1st radius of curvature)

Next, in step S50, the curvature ratio obtained in step S40 and the plate thickness obtained in step S30 are substituted into the following equations for each position of each evaluation position, and each evaluation position is obtained. Load-displacement curve.

P=P ₁ ×P _r (d)×(2.9438×t ³ +0.1875)...(1)

among them,

P _r (d)=kd ⁴ +ld ³ +md ² +nd

k=ka(Rx/Ry)+kb

l=la(Rx/Ry)+lb

m=ma(Rx/Ry)+mb

n=na(Rx/Ry)+nb

P ₁ =f ₁ (ρ _x ). ρ _y ² +f ₂ (ρ _x ). ρ _y +f ₃ (ρ _x )

ρ _x =1000/Rx

ρ _y =1000/Ry

f ₁ (ρ _x )=aa. ρ _x ² +ab. ρ _x +ac

f ₂ (ρ _x )=ab. ρ _x ² +bb. ρ _x +bc

f ₃ (ρ _x )=ac. ρ _x ² +bc. ρ _x +cc

Here, P: load (N), d: displacement (mm), Rx: second radius of curvature (mm), Ry: first radius of curvature (maximum radius of curvature) (mm), Aa, ab, ac, bb, bc, cc, ka, kb, la, lb, ma, mb, na, nb are constants.

Then, in step S60, the position at which the tensile rigidity on the panel is low is obtained based on the load-displacement curve at each evaluation position obtained in step S50. Then, decide where you need to strengthen.

In addition, when the position where the tensile rigidity is low is lower than the target minimum tensile rigidity, the curvature ratio of the minimum tensile rigidity or more aimed at the position where the tensile rigidity is low can be obtained by the inverse calculation according to the above formula, and the update is performed. The above initial setting is repeated, and the processes of the above steps S10 to S60 are repeated.

Here, the above processing can be incorporated into a computer as a series of software.

As described above, the evaluation of the tensile rigidity can be easily and with a predetermined accuracy based on the radius of curvature of the evaluation position. As a result, it is possible to determine where the panel needs to be reinforced.

Further, according to the method of the present embodiment, the load-displacement characteristic at an arbitrary position on the panel can be easily obtained. Therefore, it is possible to calculate the displacement at the time of applying an arbitrary load and the load at the time of giving an arbitrary displacement at an arbitrary point on the panel. Therefore, for example, the tensile rigidity in the case where the displacement of the panel when a very small load is applied or the load when the displacement is large is different can be easily obtained by the same formula.

In addition, each constant in the above formula may be obtained in advance by the following experiment or analysis, wherein in the above experiment, the radius of curvature of the measurement point on the panel is actually measured at a plurality of points at a time, and the measurement point is given a displacement. For the operation of measuring the load, the same method as the above experiment was used in the above analysis.

Here, the term "P ₁ ×P _r (d)" in the above formula (1) can be summarized as a function of a quadratic equation in which the curvature ratio and the displacement are variables. As will be described later, it is preferable to summarize by a function of four or more times in which the curvature ratio and the displacement are variables. Further, based on the consideration of the shape of the load-displacement curve by the curvature ratio, the above formula (1) can be classified into a first-order, a second-order or a third-order equation in which the curvature ratio and the displacement are variables, but In the case of the four-times classification, the accuracy is slightly lowered. Further, it can also be summarized by a function of five or more times in which the curvature ratio and the displacement are variables. However, the calculations will become complicated accordingly.

Further, the above-described formula of the load-displacement characteristic is a formula in which the plate thickness is a variable in addition to the curvature ratio and the displacement. In the case where the plate thickness is assumed to be fixed, the above-described equation of the load-displacement characteristic is an equation in which only the curvature ratio and the displacement are variables. Therefore, the distribution of the tensile rigidity of the panel can also be evaluated by comparing the curvature ratios of the plurality of evaluation positions. That is, the state of the tensile rigidity on the panel can also be evaluated by the curvature ratio of the plurality of evaluation positions.

(about the validity of the formula)

Then, the appropriateness of the above formula is supplemented.

The inventors and the like investigate and discuss the effect of the shape imparted to the panel by finite element analysis.

In the method, a panel having a projected area of 500 mm × 500 mm as shown in Fig. 3, that is, a panel having an upwardly convex panel having the same radius of curvature in the x direction and the y direction, was produced. In Fig. 3, the x-axis is set in the lateral direction and the y-axis is set in the longitudinal direction. Further, the center of the model is displaced vertically downward by a point load, thereby obtaining a load-displacement curve, and adjusting the curvature radius and the load-displacement relationship in the x direction and the y direction.

Here, the software used in the finite element analysis is LS-DYNA. Ver971d R3.2.1, manufactured by Livermore Software Technology Corporation, has a mesh size of about 5 mm x 5 mm and a plate thickness of 0.65 mm. The four sides of each model are completely limited. Moreover, the static implicit method is used in the analysis.

Further, at this time, among the material properties, the modulus of elasticity (Young's modulus): 210 GPa, YP (yield strength): 285 MPa, TS (tensile strength): 345 MPa, uEL (uniform elongation): 20.1%.

In addition, when the limit of the four sides of the model is 500 mm × 500 mm, if the analysis is performed until the displacement is 2 mm, the load-displacement relationship at the center portion is hardly affected.

The combination of the radius of curvature (Rx) in the x direction and the radius of curvature (Ry) in the y direction of each of the above models is performed in all combinations that allow repetition from the following eight types of curvature radii. Moreover, the upper limit of the displacement given is set to 2 mm.

Curvature radius: 8 types of 500mm, 1000mm, 1500mm, 2000mm, 5000mm, 10000mm, 15000mm, 20000mm.

First, the inventors and the like adjust the load generated when a certain displacement is given. That is, the curvature radius (Ry) in the y direction is changed for each of the set curvature radiuses (Rx) in the x direction, and the relationship between the Ry and the load at a displacement of 1 mm is obtained, and the relationship shown in Fig. 4 is obtained. In addition, the horizontal axis of FIG. 4 is ρ _y (1000/Ry) in which the curvature is 1000 times for the subsequent adjustment.

Further, according to Fig. 4, the inventors have found that "the relationship between ρ _y and the load at a displacement of 1 mm" is a substantially linear relationship, and the load required to shift by 1 mm can be adjusted by the radius of curvature.

Further, the inventors and the like have found that the curve shown in FIG. 4 can be expressed by the following equation using Rx and Ry.

ρ _x =1000/Rx

ρ _y =1000/Ry

f ₁ (ρ _x )=aa. ρ _x ² +ab. ρ _x +ac

f ₂ (ρ _x )=ab. ρ _x ² +bb. ρ _x +bc

f ₃ (ρ _x )=ac. ρ _x ² +bc. ρ _x +cc

P ₁ =f ₁ (ρ _x ). ρ _y ² +f ₂ (ρ _x ). ρ _y +f ₃ (ρ _x )

Here, aa~cc is a constant shown in Table 1.

P ₁ represents the applied load. Moreover, Table 2 is a value obtained by finite element analysis.

When the solution obtained by substituting Rx and Ry into the above formula and the load obtained by the finite element analysis shown in Table 2 are plotted as a plot, FIG. 5 is obtained. As can be seen from Fig. 5, the solution obtained by the regression equation is roughly equal to the solution of the finite element analysis.

As described above, the load at the time of displacement of 1 mm can be regressed using Rx and Ry.

Next, it is considered that the load-displacement curve is regressed based on the load at the displacement of 1 mm obtained by the above result and Rx and Ry.

Based on the results of various tests and analyses, the following findings were obtained: the shape of the load-displacement curve is strongly correlated with the ratio of Rx to Ry. Further, it has been found that the load-displacement curve is approximated by a formula in which the curvature ratio and the displacement are equal to or greater than the fourth-order function of the variable, whereby the approximation can be performed with higher precision.

If the above is summarized, the two orthogonal Rs are set to Rx and Ry. The load (P)-displacement (d) curve of the panel having curvature can be expressed by the following equation.

P=P ₁ ×P _r (d)...(2)

among them

P _r (d)=kd ⁴ +ld ³ +md ² +nd

k=ka(Rx/Ry)+kb

l=la(Rx/Ry)+lb

m=ma(Rx/Ry)+mb

n=na(Rx/Ry)+nb

P ₁ =f ₁ (ρ _x ). ρ _y ² +f ₂ (ρ _x ). ρ _y +f ₃ (ρ _x )

ρ _x =1000/Rx

ρ _y =1000/Ry

f ₁ (ρ _x )=aa. ρ _x ² +ab. ρ _x +ac

f ₂ (ρ _x )=ab. ρ _x ² +bb. ρ _x +bc

f ₃ (ρ _x )=ac. ρ _x ² +bc. ρ _x +cc

Here, P: load (N), d: displacement (mm), Rx: radius of curvature (mm), Ry: radius of curvature (mm), aa, ab, ac, bb, bc, cc, ka, kb, la , lb, ma, mb, na, nb are constants.

Aa~nb are shown in Tables 1 and 3.

Moreover, it is set to (Rx/Ry) ≦1.

In the above analysis, Rx and Ry correspond to the maximum radius of curvature and the minimum radius of curvature of the panel, respectively. The inventors and others further discovered from the analysis that the approximation of the combined load-displacement curve other than the combination of the minimum radius of curvature of the measurement point and the maximum radius of curvature is used, using the maximum radius of curvature and the direction orthogonal to the maximum radius of curvature. The ratio of the radius of curvature yields the best approximation for the approximate load-displacement curve.

Further, the coefficients described in Tables 1 and 3 are values in the case of a steel sheet having a thickness of 0.65 mm. In other words, the value of the constant aa to the constant nb may be obtained in advance based on the material of the target panel.

Further, the inventors have thought that the formula (1) can be applied to various plate thicknesses by correcting the thickness of the formula (2).

Here, in general, from the viewpoint of material mechanics, it is understood that the tensile rigidity is approximately proportional to the third power of the sheet thickness.

Therefore, in the model of the door of Fig. 6, the thickness of the outer panel is changed to analyze the tensile rigidity.

Regarding model making, the shape of the actual door is measured by a three-dimensional shape measuring instrument, and the use of Altair is used according to the data. HyperMesh to create a finite element analysis model. At this time, the mesh size is set to 15 mm for the outer panel, and 10 mm for the inner panel and other structural members. In terms of elements, the shell element is used, and the total number of elements is 20762, and the number of elements in the inner and outer panels is 4113. The thickness of the inner panel was set to 1.2 mm, the thickness of the tube disposed on the impact beam and the lower portion of the panel was set to 2.3 mm, and the thickness of the outer panel was set to 0.7 mm. The restriction condition is such that when the vehicle is mounted on the vehicle as a vehicle door, the position fixed to the vehicle body frame is completely fixed. In terms of feature types, a multi-linear approximation isotropic elastoplastic model is used. LS-DYNA ver971d R3.2.1 (manufactured by Livermore Software Technology Corporation) was used, and analysis was performed using a static implicit method.

The relationship between the sheet thickness and the tensile rigidity was determined from the analysis results of the tensile rigidity when the thickness of the outer panel was 0.7 mm, 0.65 mm, and 0.60 mm. Based on the analysis results of the above three kinds of plate thicknesses, the load at the position L, the position M, and the position U shown in FIG. 6 at a displacement of 2 mm is plotted for each plate thickness, and FIG. 7 is obtained. As can be seen from Fig. 7, the value of the tensile rigidity is approximately proportional to the third power of the plate thickness.

Here, when the thickness is 0.65 mm, the load required to shift only the amount set in advance is P (0.65), and when the same position is set to the thickness t (mm), The load required to shift only the amount set in advance is set to P(t), and P(t) can be expressed by the following equation using P(0.65).

P(t)=P(0.65)×(2.9438×t ³ +0.1875)...(3)

P (0.65) in the formula (3) is the same as P in the formula (2). Therefore, the equation for determining the load (P)-displacement (d) curve using the radius of curvature and the thickness of the plate is finally the following formula.

P=P(0.65)×(2.9438×t ³ +0.1875)=P ₁ ×P _r (d)×(2.9438×t ³ +0.1875)...(4)

The equation (4) is a function of a quadratic equation with a curvature ratio and a displacement as variables.

Example

Next, an embodiment based on the above embodiment will be described.

This embodiment is a case where the panel to be evaluated is a door panel for an automobile.

(evaluation method)

Figure 8 is a schematic cross-sectional view showing the evaluation test.

In the tensile rigidity test, the target door panel is horizontally fixed with respect to the test apparatus. As shown in FIG. 8, the height is 16 mm and φ is in the direction from the outer panel side toward the inner panel side of the door panel. A 45 mm rubber indenter applies a load so that the contact type displacement gauge measures the displacement from the back side of the door to the measurement position, thereby obtaining a load-displacement curve at each measurement position. At this time, the installation of the door panel in the test apparatus is performed such that the indenter is vertically touched with respect to the measurement position of the outer panel, and the points of the substantially four corners of the outer panel are fixed by the vise.

On the other hand, the radius of curvature is calculated from the three-dimensional shape measurement data. Rx, Ry.

The evaluation position to be compared is two points ("A" and "B" which are hardly affected by the reinforcement of the collision bar (see Fig. 9).

The radius of curvature of the position of A is Rx=3000 mm, Ry=5000 mm, and the radius of curvature of the position of B is Rx=3500 mm, and Ry=50000 mm. The outer panel has a plate thickness of 0.7 mm. Rx is the second radius of curvature, and Ry is the first radius of curvature.

Fig. 10 (a) and Fig. 10 (b) are graphs showing the measurement results of the above evaluation test and obtained by the above embodiment.

According to the results shown in Figs. 10(a) and 10(b), by applying the technique of the present invention, the load-displacement curve can be expressed with high precision only by the curvature and the thickness.

Further, in FIGS. 10(a) and 10(b), the curvature radii in the two directions deviating from the maximum radius of curvature +45 degrees and -45 degrees are substituted into the above equation (4). The result was taken as Comparative Example 1.

10(a) and 10(b), the calculation is performed based on the maximum radius of curvature and the radius of curvature in the direction orthogonal to the maximum radius of curvature, so that the experimental result can be predicted with higher precision.

In addition, as shown in FIG. 10(a) and FIG. 10(b), the curve obtained by substituting the radius of curvature and the thickness of the sheet into the formula described in Patent Document 2 is recorded as Comparative Example 2. In Comparative Example 2, although the initial slope of the load-displacement curve can be reproduced, as the displacement increases, the deviation from the experimental result increases, and it is not necessarily said that the tensile rigidity can be accurately predicted.

1‧‧‧ panel

A, B‧‧ points

H‧‧‧ Evaluation location

L, M, U‧‧‧ position

Rx, Ry‧‧ radius of curvature

S10, S20, S30, S40, S50, S60‧‧ steps

1 is a flow chart illustrating an evaluation method based on an embodiment of the present invention Figure.

FIG. 2 is a schematic diagram showing an example of an evaluation position set on a panel.

Fig. 3 is a view showing the shape of an analysis model.

4 is a view showing a relationship between a load required to shift 1 mm and a curvature in the y direction.

Figure 5 is a graph comparing the results of regression calculations with the results of finite element analysis.

Fig. 6 is a view showing a door model.

Fig. 7 is a view showing the relationship between the thickness of the plate and the load required for the displacement of 2 mm.

Figure 8 is a schematic cross-sectional view of the evaluation test apparatus.

Fig. 9 is a view showing an evaluation position of the embodiment.

10(a) and 10(b) are diagrams showing evaluation results.

Fig. 11 is a schematic view showing the relationship of load-displacement.

S10, S20, S30, S40, S50, S60‧‧ steps

Claims (3)

A panel evaluation method for estimating the tensile rigidity of a panel member having a convex shape on one side as a whole, and obtaining a first radius of curvature which is a maximum radius of curvature of the panel member set at an evaluation position of the panel member, and a second curvature radius of a curvature radius in a direction orthogonal to a curvature direction of the maximum curvature radius, and a curvature ratio obtained as a ratio of the first curvature radius to the second curvature radius obtained, and the obtained curvature ratio The plate thickness of the panel member at the position is evaluated, and the load-displacement characteristic at the evaluation position is obtained using the obtained curvature ratio and the plate thickness. The panel evaluation method according to claim 1, wherein the equation represented by the quadratic function of the curvature ratio and the displacement is used as a quadratic function, P = P ₁ × P _r (d) × (2.9438 × t ³ +0.1875), the load-displacement characteristic obtained by using the above curvature ratio and the thickness of the plate is obtained, where P _r (d)=kd ⁴ +ld ³ +md ² +nd k=ka(Rx/Ry) +kb l=la(Rx/Ry)+lb m=ma(Rx/Ry)+mb n=na(Rx/Ry)+nb P ₁ =f ₁ (ρ _x ). ρ _y ² +f ₂ (ρ _x ). ρ _y +f ₃ (ρ _x ) ρ _x =1000/Rx ρ _y =1000/Ry f ₁ (ρ _x )=aa. ρ _x ² +ab. ρ _x +ac f ₂ (ρ _x )=ab. ρ _x ² +bb. ρ _x +bc f ₃ (ρ _x )=ac. ρ _x ² +bc. ρ _x +cc here, P: load (N), d: displacement (mm), plate thickness t (mm), Rx: second radius of curvature (mm), Ry: first radius of curvature (mm), aa, Ab, ac, bb, bc, cc, ka, kb, la, lb, ma, mb, na, nb are constants. A panel evaluation method for determining a reinforcement position by evaluating a plurality of evaluation positions by a panel evaluation method as described in claim 1 or 2.