US 20020183993 A1 Abstract An FEM analysis system is provided which is capable of analyzing with high accuracy and within a short time in a drop shock analysis of electronic devices in which a very small mesh size is incorporated. Processing to be performed by an optimal solution selecting and analyzing section includes a step of checking whether an analysis to be performed is a shock analysis, a step of searching for a minimum mesh size when the analysis to be performed is judged to be a shock analysis, a step of creating a simplified analysis model using the minimum mesh size, a step of performing a preliminary analysis on a simplified model by an implicit method and explicit method, and a step of selecting either of the implicit method or explicit method as an optimal analysis method by comparing results from preliminary analysis, results from these analyses and experiments or exact solution.
Claims(21) 1. An analysis method using a finite element method for performing a stress analysis on an analysis model, comprising:
a first step of judging whether or not an analysis to be made is a shock analysis; a second step of performing an analysis using an implicit method when said analysis to be made is judged to be a shock analysis in said first step; and a third step of performing an analysis using an analysis method selected by an analyzer when said analysis to be made is judged to be not a shock analysis in said first step. 2. The analysis method using the finite element method according to 3. An analysis method using a finite element method for creating meshes of an analysis model and for making a stress analysis of said analysis model, said analysis method comprising:
a first step of judging whether an analysis to be made is a shock analysis; a second step of searching for a minimum mesh size out of said meshes of said analysis model; a third step of creating a simplified analysis model using said minimum mesh size; a fourth step of analyzing said simplified analysis model by using an implicit method and an explicit method; a fifth step of selecting either of said implicit method or said explicit method as an optimal method, based on a result from an analysis in said fourth step; a sixth step of having an analyzer select either of said implicit method or said explicit method based on a result from said analysis in said fourth step; and a seventh step of analyzing said analysis model by using an analysis method selected in said fifth step or said sixth step. 4. The analysis method using the finite element method according to 5. The analysis method using the finite element method according to T
_{im} <T
_{ex } where said “T
_{im}” denotes analysis time required for said implicit method and said “T_{ex}” denotes analysis time required for said explicit method, said implicit method is selected while, when above said expression does not hold, said explicit method is selected. 6. The analysis method using the finite element method according to abs(E−S _{im})<abs(E−S _{ex}) where said “abs” denotes an absolute value, said “S
_{im}” denotes an analysis result containing data on displacement, stress, and distortion obtained from said implicit method, said “S_{ex}” denotes an analysis result containing data on displacement, stress, and distortion obtained from said explicit method, and said “E” denotes a result containing data on displacement, stress, and distortion obtained from said implicit method including an experiment value and an exact solution of a theoretical expression and from a method other than said explicit method, said implicit method is selected while, when above said expression does not hold, said explicit method is selected. 7. The analysis method using the finite element method according to _{im}” and analysis time required for said explicit method said “T_{ex}” and based on a relation among an analysis result said “S_{im}” containing displacement, stress, and distortion obtained from said implicit method, an analysis result said “S_{ex}” containing displacement, stress, and distortion obtained from said explicit method, and a result said “E” containing displacement, stress, and distortion obtained from said implicit method including an experiment value and an exact solution of a theoretical expression and from a method other than said explicit method. 8. A program for having a computer make an analysis using a finite element method used to perform a stress analysis of an analysis model: said program comprising:
a first step of judging whether or not an analysis to be made is a shock analysis; a second step of performing an analysis using an implicit method when said analysis to be made is judged to be a shock analysis in said first step; a third step of performing an analysis by using an analysis method selected by an analyzer when said analysis to be made is judged to be not a shock analysis in said first step. 9. The program according to 10. A program for having a computer execute an analysis using a finite element method which creates meshes of an analysis model and performs a stress analysis of said analysis model, said program comprising:
a first process of judging whether or not an analysis to be performed is a shock analysis; a second process of searching for a minimum mesh size out of said meshes of said analysis model; a third process of creating a simplified analysis model using said minimum mesh size; a fourth process of analyzing said simplified analysis model by using an implicit method and an explicit method; a fifth process of selecting either of said implicit method or said explicit method as an optimal method, based on a result from said analysis in said fourth process; a sixth process of having an analyzer select either of said implicit method or said explicit method based on a result from said analysis in said fourth process; and a seventh process of analyzing said analysis model by using an analysis method selected in said fifth process or said sixth process. 11. The program according to 12. The program according to T
_{im} <T
_{ex } where said “T
_{im}” denotes analysis time required for said implicit method and said “T_{ex}” denotes analysis time required for said explicit method, said implicit method is selected while, when above said expression does not hold, said explicit method is selected. 13. The program according to abs(E−S _{im})<abs(E−S _{ex}) where said “abs” denotes an absolute value, said “S
_{im}” denotes an analysis result containing data on displacement, stress, and distortion obtained from said implicit method, S_{ex }said denotes an analysis result containing data on displacement, stress, and distortion obtained from said explicit method, and said “E” denotes a result containing data on displacement, stress, and distortion obtained from said implicit method including an experiment value and an exact solution of a theoretical expression and from a method other than said explicit method, said implicit method is selected while, when above said expression does not hold, said explicit method is selected. 14. The program according to _{im}” and said analysis time required for said explicit method said “T_{ex}” and based on a relation among an analysis result said “S_{im}” containing displacement, stress, and distortion obtained from said implicit method, an analysis result said “S_{ex}” containing displacement, stress, and distortion obtained from said explicit method, and a result said “E” containing displacement, stress, and distortion obtained from said implicit method including an experiment value and an exact solution of a theoretical expression and from a method other than said explicit method. 15. A finite element method analysis system having a unit for creating meshes of an analysis model and having a unit for making an analysis using a finite element method used to perform a stress analysis on said analysis model using said finite element method, said finite element method analysis system comprising:
a first unit to judge whether or not an analysis to be made is a shock analysis; wherein, when said analysis to be performed by said unit for making said analysis using said finite element method is judged by said first unit to be a shock analysis, an analysis is made by using an implicit method and wherein, when said analysis to be performed by said unit making said analysis using said finite element method is judged by said first unit to be not a shock analysis, said analysis is made by using an analysis method selected by an analyzer. 16. The finite element method analysis system according to 17. A finite element method analysis system having a unit for creating meshes of an analysis model and having a unit for making an analysis using a finite element method used to perform a stress analysis on said analysis model using said finite element method, said finite element method analysis system comprising:
a first section to judge whether or not an analysis to be performed is a shock analysis; a second section to search for a minimum mesh size out of said meshes of said analysis model; a third section to create a simplified analysis model using said minimum mesh size; a fourth section to select either of said implicit method or said explicit method as an optimal method, based on a result from a simplified analysis in which said simplified analysis model is analyzed by a unit for making an analysis using a finite element method by using an implicit method and an explicit method; a fifth section to have an analyzer select either of said implicit method or said explicit method as an analysis method based on a result from said simplified analysis; and wherein said unit for making an analysis using a finite element method analyzes said analysis model by using said fourth section or said fifth section. 18. The finite element method analysis system according to 19. The finite element method analysis system according to T
_{im} <T
_{ex } where said “T
_{im}” denotes analysis time required for said implicit method and said “T_{ex}” denotes analysis time required for said explicit method, selects said implicit method while, when above said expression does not hold, selects said explicit method. 20. The finite element method analysis system according to abs(E−S _{im})<abs(E−S _{ex}) where said “abs” denotes an absolute value, said “S
_{im}” denotes an analysis result containing data on displacement, stress, and distortion obtained from said implicit method, said S_{ex }denotes an analysis result containing data on displacement, stress, and distortion obtained from said explicit method, and said “E” denotes a result containing data on displacement, stress, and distortion obtained from said implicit method including an experiment value and an exact solution of a theoretical expression and from a method other than said explicit method, selects said implicit method while, when above said expression does not hold, selects said explicit method. 21. The finite element method analysis system according to _{im}” and analysis time required for said explicit method said “T_{ex}” and based on a relation among an analysis result said “S_{im}” containing displacement, stress, and distortion obtained from said implicit method, an analysis result said “S_{ex}” containing displacement, stress, and distortion obtained from said explicit method, and a result said “E” containing displacement, stress, and distortion obtained from said implicit method including an experiment value and an exact solution of a theoretical expression and from a method other than said explicit method.Description [0001] 1. Field of the Invention [0002] The present invention relates to a drop shock analysis system using an FEM (Finite Element Method) and more particularly to an analysis method using the FEM for analyzing a drop shock of an electronic device, a program for the analysis by the FEM method, and an FEM analysis system. [0003] The present application claims priority of Japanese Patent Application No.2001-164730 filed on May 31, 2001, which is hereby incorporated by reference. [0004] 2. Description of the Related Art [0005] Since it is expected that, by using a stress analysis (by way of simulation) based on an FEM, a number of times of manufacturing a prototype and of experiments can be reduced and a development period can be shortened, the stress analysis using the FEM is now being carried out increasingly in businesses or universities. [0006] The stress analysis can be classified into two types, one being a static analysis and another being a dynamic analysis. A method for the stress analysis can also be classified into two types, one being an implicit method and another being an explicit method. These two methods are different from each other in that an expression of the implicit method contains a spring constant “k” as a matrix, thereby forming a non-diagonal matrix and an expression of the explicit method contains a mass “m” as a matrix, thereby forming a diagonal matrix. Therefore, when the stress analysis is performed, an inverse matrix calculation of the spring constant “k” takes more time than an inverse matrix calculation of the mass “m”. Moreover, in the case of the implicit method, a simultaneous linear equation is solved so that an equilibrium condition is satisfied and therefore accuracy of a stress analysis is higher compared with the explicit method, however, more time is required for the analysis compared with the explicit method. [0007] Each of the implicit and explicit methods has an advantage and a disadvantage. As a result, the implicit method is used for the static analysis not requiring so much time and the explicit method is used, in most cases, for the dynamic analysis requiring much time. Under present circumstances, in an automobile industry having a most advanced drop shock (crash) analysis technology being a field of the present invention, in particular, the stress analysis is performed by using an explicit method-specific software typified by PAM-SHOCK and LS-DYNA. FIG. 4 is a flowchart showing one example of the analysis processing operation in a conventional FEM analysis system. That is, in Step A [0008] In such circumstances, sizes and weights of electronic devices are being reduced rapidly in recent years and a cellular phone or a like becomes widespread remarkably in particular, however, a problem occurs in that, when it is dropped while carrying it, a connected portion of an LSI chip embedded therein is broken. In order to evaluate connection reliability of portable electronic devices, an actual drop test is required using actual electronic devices, however, the experiment entails high costs and time. Therefore, a demand for reduction in costs required in such experiments for a drop shock analysis is increasing. In an attempt to respond to this demand, a method using a shock analysis technique cultivated through experiences in automobiles was tried by some universities, however, values calculated in experiments are not in agreement with actual phenomena, for example, reaction force (impact force) is extraordinarily larger (that is, larger by one to two digits) than calculated values and it is therefore expected that a new method of an analysis of a drop shock that can be used for the analysis of electronic devices is developed. [0009] A reason why behavior (deformation of each part) and reaction force (impact force) are widely different from actual phenomena when the explicit method is used for a dynamic analysis, in particular, for a drop analysis of portable electronic devices is explained below. [0010] When “Δt Δ c=( [0011] where “L” denotes a minimum mesh size in an analysis model, “c” denotes a propagation speed of an elastic wave, “E” denotes a longitudinal elastic modulus (also being called “Young's modulus”) and “ρ” denotes mass density. Thus, since the explicit method has a property that it depends on the analysis time interval Δt α≈ [0012] where “α” denotes acceleration, “m” denotes a mass, “F” denotes reaction force, and “v” denotes a drop velocity. As a result, the calculation produces extremely large reaction force (impact force) F and different deformation occurs. [0013] As one example, when a body is dropped from a height of 1000 mm, due to a law of conservation of energy, a following equation (6) is given: [0014] where “g” denotes gravimetric acceleration and “h” denotes a dropped height. Since a phenomenon of about 5×10 α=4400×10000/5=8×10 [0015] As a convergence stabilizing condition in the explicit method, the analysis time interval Δt Δ [0016] If a solder ball diameter is 1.0 mm, a Young's modulus E=19600 N/mm [0017] Therefore, in order to analyze a drop phenomenon at a speed of 5×10 [0018] As described above, if an analysis time interval is same, since a number of times of the analysis required to reach the value of 5×10 [0019] However, if the analysis time interval required for satisfying conditions for stabilization in the explicit method becomes extraordinarily smaller compared with that in the implicit method because a fine mesh is contained like in the case of a model for portable electronic devices, a number of times of the explicit method (analysis time interval in the implicit method/analysis time interval in the explicit method)×(number of times in the implicit method). As a result, due to an increased number of the analysis in the explicit method, time required for the total analysis is increased more in the explicit method compared with the implicit method. [0020] Moreover, in the analysis during the very short time interval, there are some cases in which shock force increases and deformation state is not in agreement with an actual phenomenon. In the above example, in the case of the implicit method, a value approaching to a result from a calculation on paper can be acquired by using a shock force of about 980N, however, in the case of the explicit method, about one hundred-folded shock force is necessary. [0021] In view of the above, it is an object of the present invention to provide an FEM analysis system which is capable of analyzing with high accuracy and with a short time in a drop shock analysis of electronic devices or a like in which an analysis result is very different from actual phenomena and in which a very small mesh size is incorporated. [0022] According to a first aspect of the present invention, there is provided an analysis method using a finite element method for performing a stress analysis on an analysis model, including: [0023] a first step of judging whether or not an analysis to be made is a shock analysis; [0024] a second step of performing an analysis using an implicit method when the analysis to be made is judged to be a shock analysis in the first step; and [0025] a third step of performing an analysis using an analysis method selected by an analyzer when the analysis to be made is judged to be not a shock analysis in the first step. [0026] With the above configuration, whether or not an analysis to be made is a shock analysis is judged and when it is judged to be a shock analysis, an analysis is made using the implicit method. Therefore, a shock analysis using the explicit method is not performed in which a decrease in accuracy in an analysis and an increase in analysis time occur when a mesh size is made minute and an FEM analysis using the implicit method is made in which a result from an analysis approaching to a real phenomena can be obtained within a short time. [0027] In the foregoing, a preferable mode is one wherein a Newmark β method is used as the implicit method. [0028] According to a second aspect of the present invention, there is provided an analysis method using a finite element method for creating meshes of an analysis model and for making a stress analysis of the analysis model, the analysis method including: [0029] a first step of judging whether an analysis to be made is a shock analysis; [0030] a second step of searching for a minimum mesh size out of the meshes of the analysis model; [0031] a third step of creating a simplified analysis model using the minimum mesh size; [0032] a fourth step of analyzing the simplified analysis model by using an implicit method and an explicit method; [0033] a fifth step of selecting either of the implicit method or the explicit method as an optimal method, based on a result from an analysis in the fourth step; [0034] a sixth step of having an analyzer select either of the implicit method or the explicit method based on a result from the analysis in the forth step; and [0035] a seventh step of analyzing the analysis model by using an analysis method selected in the fifth step or the sixth step. [0036] With the above configuration, a simplified analysis model using a minimum mesh size of an analysis model is analyzed by the implicit method and explicit method. Based on a result from the analysis, either of the implicit method or the explicit method is selected as an optimal method and an FEM analysis is made by using the selected analysis method. Moreover, the analysis method can be selected by an analyzer and therefore it is possible to execute the FEM analysis in consideration of demands required for an analysis such as a desire for shortening analysis time or a desire for placing importance on analysis accuracy. [0037] In the foregoing, a preferable mode is one wherein a Newmark β method is used as the implicit method. [0038] Also, a preferable mode is one wherein, in the fifth step, when a following expression holds, T [0039] Where the “T [0040] Also, a preferable mode is one wherein, in the fifth step, when a following expression holds, [0041] where the “abs” denotes an absolute value, the “S [0042] Also, a preferable mode is one wherein, in the sixth step, the analyzer is allowed to select an analysis method based on a relation between analysis time required for the implicit method “T [0043] According to a third aspect of the present invention, there is provided a program for having a computer make an analysis using a finite element method used to perform a stress analysis of an analysis model: the program including; [0044] a first step of judging whether or not an analysis to be made is a shock analysis; [0045] a second step of performing an analysis using an implicit method when the analysis to be made is judged to be a shock analysis in the first step; [0046] a third step of performing an analysis by using an analysis method selected by an analyzer when the analysis to be made is judged to be not a shock analysis in the first step. [0047] In the foregoing, a preferable mode is one wherein a Newmark β method is executed by a computer as the implicit method. [0048] According to a fourth aspect of the present invention, there is provided a program for having a computer execute an analysis using a finite element method which creates meshes of an analysis model and performs a stress analysis of the analysis model, the program including: [0049] a first process of judging whether or not an analysis to be performed is a shock analysis; [0050] a second process of searching for a minimum mesh size out of the meshes of the analysis model; [0051] a third process of creating a simplified analysis model using the minimum mesh size; [0052] a fourth process of analyzing the simplified analysis model by using an implicit method and an explicit method; [0053] a fifth process of selecting either of the implicit method or the explicit method as an optimal method, based on a result from the analysis in the fourth process; [0054] a sixth process of having an analyzer select either of the implicit method or the explicit method based on a result from the analysis in the fourth process; and [0055] a seventh process of analyzing the analysis model by using an analysis method selected in the fifth process or the sixth process. [0056] In the foregoing, a preferable mode is one wherein a Newmark β method is executed by a computer as the implicit method. [0057] Also, a preferable mode is one wherein, in the fifth process, when a following expression holds,
[0058] Where the “T [0059] Also, a preferable mode is one wherein, in the fifth process, when a following expression holds, [0060] where the “abs” denotes an absolute value, the “S [0061] Also, a preferable mode is one wherein, in the sixth process, the analyzer is allowed to select an analysis method based on a relation between the analysis time required for the implicit method “T [0062] According to a fifth aspect of the present invention, there is provided a finite element method analysis system having a unit for creating meshes of an analysis model and having a unit for making an analysis using a finite element method used to perform a stress analysis on the analysis model using the finite element method, the finite element method analysis system including: [0063] a first unit to judge whether or not an analysis to be made is a shock analysis; [0064] wherein, when the analysis to be performed by the unit for making the analysis using the finite element method is judged by the first unit to be a shock analysis, an analysis is made by using an implicit method and wherein, when the analysis to be performed by the unit making the analysis using the finite element method is judged by the first unit to be not a shock analysis, the analysis is made by using an analysis method selected by an analyzer. [0065] In the foregoing, a preferable mode is one wherein the unit making the analysis using the finite element method performs a Newmark β method as the implicit method. [0066] According to a sixth aspect of the present invention, there is provided a finite element method analysis system having a unit for creating meshes of an analysis model and having a unit for making an analysis using a finite element method used to perform a stress analysis on the analysis model using the finite element method, the finite element method analysis system including: [0067] a first section to judge whether or not an analysis to be performed is a shock analysis; [0068] a second section to search for a minimum mesh size out of the meshes of the analysis model; [0069] a third section to create a simplified analysis model using the minimum mesh size; [0070] a fourth section to select either of the implicit method or the explicit method as an optimal method, based on a result from a simplified analysis in which the simplified analysis model is analyzed by a unit for making an analysis using a finite element method by using an implicit method and an explicit method; [0071] a fifth section to have an analyzer select either of the implicit method or the explicit method as an analysis method based on a result from the simplified analysis; and [0072] wherein the unit for making an analysis using a finite element method analyzes the analysis model by using the fourth section or the fifth section. [0073] In the foregoing, a preferable mode is one wherein the unit making the analysis using the finite element method performs a Newmark β method as the implicit method. [0074] Also, a preferable mode is one wherein, the fourth section, when a following expression holds,
[0075] where the “T [0076] Also, a preferable mode is one wherein, the fourth section, when a following expression holds, [0077] where the “abs” denotes an absolute value, the “S [0078] Also, a preferable mode is one wherein the fifth section has the analyzer select an analysis method based on a relation between analysis time required for the implicit method “T [0079] With the above configuration, whether an analysis is made by the explicit method or whether the analysis is made by the implicit method can be selected according to an analysis model. Since an analysis can be performed on an analysis model using an optimal method, an analysis result can be obtained with high accuracy and within a short time. [0080] The above and other objects, advantages, and features of the present invention will be more apparent from the following description taken in conjunction with the accompanying drawings in which; [0081]FIG. 1 is a schematic diagram showing an FEM analysis system according to a first embodiment of the present invention; [0082]FIG. 2 is a flowchart showing a processing operation to be performed by an optimal solution selecting and analyzing section in the FEM analysis system of the first embodiment of the present invention; [0083]FIG. 3 is a flowchart showing a processing operation to be performed by an optimal solution selecting and analyzing section in an FEM analysis system of the second embodiment of the present invention; and [0084]FIG. 4 is a flowchart showing one example of a processing operation in a conventional FEM analysis system. [0085] Best modes of carrying out the present invention will be described in further detail using various embodiments with reference to the accompanying drawings. [0086]FIG. 1 is a schematic block diagram showing an FEM analysis system according to an embodiment of the present invention. As shown in FIG. 1, the FEM analysis system of the embodiment includes an analysis model creating section [0087] Rough operations of each of the above sections are as follows. [0088] The analysis model creating section [0089] The analysis model data registering section [0090] The optimal solution selecting and analyzing section [0091] Finally, the analysis data registering section [0092] Next, operations of the entire FEM analysis system are described in detail by referring to the block diagram in FIG. 1 and to the flowchart in FIG. 2. [0093] As shown in the schematic block diagram in FIG. 1, in the analysis model creating section [0094] Next, in the analysis model data registering section [0095] Moreover, in the optimal solution selecting and analyzing section [0096] Finally, in the analysis data registering section [0097] Especially, a method for selecting an optimal solution and for analyzing by the optimal solution selecting and analyzing section [0098] First, in a step (A [0099] Moreover, in the optimal solution selecting and analyzing section [0100] As explained above, in the embodiment, when a shock analysis is performed on electronic device models or a like having a portion with a very small mesh size, an analysis using the implicit method is selected. Therefore, by using the FEM analysis system of the embodiment of the present invention, unlike in the case of using the FEM analysis system using the explicit method in which a decrease in analysis accuracy and an increase in analysis time occur when a mesh size becomes minute, a highly accurate analysis result approaching to a real phenomenon can be obtained within a short time. [0101] Processing in an FEM analysis system of a second embodiment is same as that of the first embodiment except processing to be performed in an optimal solution selecting and analyzing section [0102]FIG. 3 is a flowchart showing processing operations to be performed by the optimal solution selecting and analyzing section [0103] As shown in the flowchart in FIG. 3, the optimal solution selecting and analyzing section [0104] Next, operations of an entire FEM analysis system will be described by referring to the flowchart in FIG. 3. [0105] First, in the step (A [0106] If an analysis to be made is judged to be a shock analysis and the routine proceeds to a step (A [0107] Next, an analysis method is determined in a step (A T [0108] where “T [0109] Thus, by using the expression (1) as a reference for selection of the analysis method, a method that can perform an analysis within a short time can be selected. [0110] Moreover, selection of the analysis method in a step (A [0111] That is, if a following expression (2) holds, an analysis is made by using a model causing the analysis to be performed in the step (A [0112] where the “abs” denotes an absolute value, “S [0113] Thus, by using an analysis method given by the expression (2) as a reference for selection, a simplified model based on a minimum mesh size of a model to be analyzed can be created, a preliminary analysis can be made by actually using both methods, an analysis method having less errors can be selected by making a comparison between an analysis result obtained by the preliminary analysis and a result obtained from an experiment or an exact solution, which enable highly accurate acquirement of analysis results. [0114] The method that can satisfy the expressions.(1) and the method that can satisfy the expression (2) are not always same and, in the case of the analysis handling enormous numbers of meshes, even if some discrepancies occur between results obtained by using the above methods and results obtained by experiments, it is possible to select a method which requires less time. [0115] To respond to such cases, an analyzer may select an analysis method by adding the step A [0116] As described above, in the first embodiment as shown by the flowchart in FIG. 2, if, an analysis to be performed, in step A [0117] Thus, according to the FEM analysis system of the second embodiment, like in the case of the first embodiment, when a shock analysis to be performed on electronic device models or a like having portions being very small in a mesh size is made, an analysis result approaching to actual phenomena can be obtained with high accuracy within a short time. Moreover, in the FEM analysis system of the second embodiment, after a simplified model has been created based on a minimum mesh size of a model to be analyzed, a preliminary analysis using both the methods and therefore an optimal method to be applied to an individual model can be selected with high accuracy. [0118] It is apparent that the present invention is not limited to the above embodiments but may be changed and modified without departing from the scope and spirit of the invention. Referenced by
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