Method and system for modeling spot welds in a finite element analysis

A system, method and software product for modeling spot welds in a finite element analysis is described. The spots welds are represented by beam elements or solid elements in accordance with an indicator flag. The flag may also be specified as the number (e.g., an integer such as 1, 4, 8 or 16) of solid elements in a cluster representing spot weld. The solid elements may include, but not limited to, hexahedron, tetrahedron, and the likes. The number of solid elements and required nodes are generated for each spot weld based on the indicator flag. A table is formed to group the generated solid elements in a cluster together, so that the force and moment resultants of the spot weld can be computed and assembled in a file.

BACKGROUND

1. Field of the Invention

The present invention generally relates to a method, system and software product used in computer-aided engineering analysis of a structure, more particularly to modeling spot welds in a finite element analysis.

2. Description of the Related Art

Finite element analysis (FEA) is a computerized method widely used in industry to model and solve engineering problems relating to complex systems such as three-dimensional non-linear structural design and analysis. FEA derives its name from the manner in which the geometry of the object under consideration is specified. With the advent of the modern digital computer, FEA has been implemented as FEA software. Basically, the FEA software is provided with a model of the geometric description and the associated material properties at each point within the model. In this model, the geometry of the system under analysis is represented by solids, shells and beams of various sizes, which are called elements. The vertices of the elements are referred to as nodes. The model is comprised of a finite number of elements, which are assigned a material name to associate with material properties. The model thus represents the physical space occupied by the object under analysis along with its immediate surroundings. The FEA software then refers to a table in which the properties (e.g., stress-strain constitutive equation, Young's modulus, Poisson's ratio, thermo-conductivity) of each material type are tabulated. Additionally, the conditions at the boundary of the object (i.e., loadings, physical constraints, etc.) are specified. In this fashion a model of the object and its environment is created.

FEA is becoming increasingly popular with automobile manufacturers for optimizing both the aerodynamic performance and structural integrity of vehicles. Similarly, aircraft manufacturers rely upon FEA to predict airplane performance long before the first prototype is built. Rational design of semiconductor electronic devices is possible with Finite Element Analysis of the electrodynamics, diffusion, and thermodynamics involved in this situation. FEA is utilized to characterize ocean currents and distribution of contaminants. FEA is being applied increasingly to analysis of the production and performance of such consumer goods as ovens, blenders, lighting facilities and many plastic products. In fact, FEA has been employed in as many diverse fields as can be brought to mind, including plastics mold design, modeling of nuclear reactors, analysis of the spot welding process, microwave antenna design, simulating of car crash and biomedical applications such as the design of prosthetic limbs. In short, FEA is utilized to expedite design, maximize productivity and efficiency, and optimize product performance in virtually every stratum of light and heavy industry. This often occurs long before the first prototype is ever developed.

One of the most challenging FEA tasks is to simulate an impact event such as car crash or metal forming. In a typical car, there are about 4,000-8,000 spot welds connecting 300-600 body parts to form the vehicle structure. For accurate simulation of the vehicle as a whole, those spot welds have to be modeled accurately. Spot welds are typically placed 2-3 centimeters apart, and each spot weld has a diameter between 4 to 9 millimeters. Traditionally, each of the spot welds has been modeled with a very short beam element (e.g., length of 1-2 millimeters) in FEA. As the modern computer improves, the finite element models representing a vehicle have become huge (e.g., more than 1,000,000 elements). Thereby, the size of each element becomes much smaller. Representing spot welds using beam elements are not adequate any more, instead solid elements are used. In certain cases, spot welds have been modeled with more than one solid element. As a result, it is very tedious and time consuming to create a cluster of solid elements to represent a single spot weld, when there are thousands of spot welds in one vehicle.

It is therefore desirable to have new improved method and system for generating solid elements to represent spot welds using the traditional spot weld input definition in a finite element analysis.

SUMMARY

This section is for the purpose of summarizing some aspects of the present invention and to briefly introduce some preferred embodiments. Simplifications or omissions in this section as well as in the abstract and the title herein may be made to avoid obscuring the purpose of the section. Such simplifications or omissions are not intended to limit the scope of the present invention.

The present invention discloses a system, method and software product for. According to one aspect, each of the spot welds is specified in the input file (e.g., a beam element) of an engineering analysis or simulation software module (e.g., a finite element analysis software). To facilitate the software module using solid elements to represent spot welds, an indicator flag is specified in the spot weld input definitions (e.g., the control card in spot weld beam). When the indicator flag has a default value of zero, beam elements are used. Otherwise solid elements are used. According to another aspect, if solid elements are chosen to represent spot welds, the number of solid elements in each cluster is determined. The required nodes and solid elements are generated in accordance with the number of the solid element in each cluster. A cluster of solid elements is then grouped together in a table, so that force and moment resultants can be computed and assembled for each of the spot weld.

According to one embodiment, the present invention is a method for modeling spot welds in a finite element analysis of a structure, the method includes at least the following: receiving an indicator flag; when the flag indicates solid element clusters to represent the spot welds, determining number of solid elements in each of the clusters; generating solid elements and required nodes in accordance with the number in said each of the clusters; and grouping the generated solid elements together for said each of the clusters; and when the flag indicates beam elements to model the spot welds, creating a beam element definition representing each of the spot welds.

One of objects, features, and advantages of the present invention is to use solid elements to represent spot welds without major modifications to the traditionally used beam element definitions in a finite element analysis.

DESCRIPTION

To facilitate the description of the present invention, it deems necessary to provide definitions for some terms that will be used throughout the disclosure herein. It should be noted that the definitions following are to facilitate the understanding and describe the present invention according to an embodiment. The definitions may appear to include some limitations with respect to the embodiment, the actual meaning of the terms has applicability well beyond such embodiment, which can be appreciated by those skilled in the art:

FEA stands for Finite Element Analysis.

Implicit FEA refers to K u=F, where K is the effective stiffness matrix, u is the unknown displacement array and F is the effective loads array. F is a right hand side loads array while K is a left hand side stiffness matrix. The solution is performed at the global level with a factorization of the effective stiffness matrix, which is function of the stiffness, mass and damping. One exemplary solution method is the Newmark integration scheme.

Explicit FEA refers to M a=F, where M is the diagonal mass array, a is the unknown nodal acceleration array and F is the effective loads array. The solution can be carried out at element level without factorization of a matrix. One exemplary solution method is called the central difference method.

Beam element refers to a one-dimensional finite element defined by two nodes.

Solid element refers to a three-dimensional finite element with volume. Typical solid elements may include, but not be limited to, tetrahedron, hexahedron, and the likes.

Referring now to the drawings, in which like numerals refer to like parts throughout several views. The present invention may be implemented using hardware, software or a combination thereof and may be implemented in a computer system or other processing system. In fact, in one embodiment, the invention is directed towards one or more computer systems capable of carrying out the functionality described herein. An example of a computer system100is shown inFIG. 1A. The computer system100includes one or more processors, such as processor122. The processor122is connected to a computer system internal communication bus120. Various software embodiments are described in terms of this exemplary computer system. After reading this description, it will become apparent to a person skilled in the relevant art(s) how to implement the invention using other computer systems and/or computer architectures.

Computer system100also includes a main memory108, preferably random access memory (RAM), and may also include a secondary memory110. The secondary memory110may include, for example, one or more hard disk drives112and/or one or more removable storage drives114, representing a floppy disk drive, a magnetic tape drive, an optical disk drive, etc. The removable storage drive114reads from and/or writes to a removable storage unit118in a well-known manner. Removable storage unit118, represents a floppy disk, magnetic tape, optical disk, etc. which is read by and written to by removable storage drive114. As will be appreciated, the removable storage unit118includes a computer usable storage medium having stored therein computer software and/or data.

In alternative embodiments, secondary memory110may include other similar means for allowing computer programs or other instructions to be loaded into computer system100. Such means may include, for example, a removable storage unit122and an interface120. Examples of such may include a program cartridge and cartridge interface (such as that found in video game devices), a removable memory chip (such as an EPROM, or PROM) and associated socket, and other removable storage units122and interfaces120which allow software and data to be transferred from the removable storage unit122to computer system100. In general, Computer system100is controlled and coordinated by operating system (OS) software, which performs tasks such as process scheduling, memory management, networking and I/O services. Exemplary OS includes Linux®, Microsoft Windows®.

There may also be a communications interface124connecting to the bus102. Communications interface124allows software and data to be transferred between computer system100and external devices. Examples of communications interface124may include a modem, a network interface (such as an Ethernet card), a communications port, a PCMCIA slot and card, etc. Software and data transferred via communications interface124are in the form of signals128which may be electronic, electromagnetic, optical, or other signals capable of being received by communications interface124. These signals128are provided to communications interface124via a communications path (i.e., channel)126. This channel126carries signals (or data flows)128and may be implemented using wire or cable, fiber optics, a phone line, a cellular phone link, an RF link and other communications channels.

The channel126facilitates a data flow128between a data network and the computer100and typically executes a special set of rules (i.e., a protocol) to send data back and forth. One of the common protocols is TCP/IP (Transmission Control Protocol/Internet Protocol) commonly used in the Internet. In general, the communication interface124manages the assembling of a data file into smaller packets that are transmitted over the data network or reassembles received packets into the original data file. In addition, the communication interface124handles the address part of each packet so that it gets to the right destination or intercepts packets destined for the computer100.

In this document, the terms “computer program medium” and “computer usable medium” are used to generally refer to media such as removable storage drive114, a hard disk installed in hard disk drive112, and signals128. These computer program products are means for providing software to computer system100. The invention is directed to such computer program products.

The computer system100may also include an I/O interface130, which provides the computer system100to access monitor, keyboard, mouse, printer, scanner, plotter, and alike.

Computer programs (also called computer control logic) are stored as application modules106in main memory108and/or secondary memory110. Computer programs may also be received via communications interface124. Such computer programs, when executed, enable the computer system100to perform the features of the present invention as discussed herein. In particular, the computer programs, when executed, enable the processor104to perform features of the present invention. Accordingly, such computer programs represent controllers of the computer system100.

In an embodiment where the invention is implemented using software, the software may be stored in a computer program product and loaded into computer system100using removable storage drive114, hard drive112, or communications interface124. The application module106, when executed by the processor104, causes the processor104to perform the functions of the invention as described herein.

The main memory108may be loaded with one or more application modules106that can be executed by one or more processors104with or without a user input through the I/O interface130to achieve desired tasks. In operation, when at least one processor104executes one of the application modules106, the results are computed and stored in the secondary memory110(i.e., hard disk drive112). The status of the finite element model definition (e.g., the spot weld definitions) is reported to the user via the I/O interface130either as a list or a graph.

In one embodiment, an application module106is configured to facilitate generation of solid elements representing spot welds. As an indication flag is detected, the application module106replaces the beam definition with one or more solid elements. In another embodiment, a plurality of solid elements is grouped together as a cluster to represent one spot weld.

FIG. 1Bdepicts a networked computing environment140, in which one embodiment of the present invention may be practiced. A plurality of network capable computing devices152,154,156,158and160(e.g., the computer device100described inFIG. 1A) are coupled to a data network150. These computing devices152-160can communicate with each other via the network150. The data network150may include, but is not limited to, the Internet, an Intranet, local area network (LAN), wide area network (WAN), a wireless network or a data network comprises of public and private networks. In one embodiment, the application module (i.e.,106inFIG. 1A) for an engineering analysis (e.g., finite element analysis) is configured and executed on a computing device156. The user prepares the input file using a pre-processing software module also located on the device156. And the analysis is performed and the output of the analysis is fed to a post-processing module to present the results either in numerical or graphical form. In another embodiment, the application module for an engineering analysis is configured and executed on the computing device160. A user may prepare an input file describing physical structure (e.g., a vehicle, spot welds, etc.) on a personal workstation computing device152. The input file is then sent to the computing device160via the network150to facilitate the computation of the engineering analysis. During the execution of the application module, the user may be able to monitor the progress of the analysis at another computing device156. Finally after the analysis is completed, the user may examine the computed results by retrieving the stored result file from the computer160to any one of the computing devices152,154or156for a post-processing, which in general includes a graphical representation of the analysis results. One exemplary implementation of this technique is included in a suite of engineering analysis computer software products, LS-PREPOST® and LS-DYNA®, offered by Livermore Software Technology Corporation, Livermore, Calif., USA.

FIG. 2shows an exemplary beam and an exemplary solid element in accordance with one embodiment of the present invention. The Beam element202is a one-dimensional element defined by two nodes. Traditionally a very short (e.g., 1-2 mm length) beam element is used to model a spot weld connecting two metal parts in a structure (e.g., a vehicle). More recently, a spot weld may be modeled with one or more solid elements (e.g., hexahedron204) in a cluster. The solid elements representing the same spot weld are grouped together, so that the resultant force and moment of the cluster (i.e., the spot weld) can be reported.

FIG. 3shows several exemplary solid element clusters in accordance with one embodiment of the present invention. Spot welds can be represented by one or more solid elements in a cluster. Exemplary hexahedron element clusters302,304,306, and308depicted inFIG. 3are for 1-, 4-, 8- and 16-elements, respectively. Although only four exemplary clusters are shown, the present invention does not limit these four types. Other arrangements will be appreciated by those skilled in the art. Similarly, other types of the solid elements such as tetrahedron can be implemented in the present invention.

FIG. 4shows an exemplary spot weld definition used in a finite element analysis software module. In accordance with one embodiment of the present invention, an indicator flag (e.g., RPBHX404) of a control card402for spot weld is used for determining whether beam or solid elements to be used in the finite element analysis. For example, the indicator flag404may have a default value of zero, which causes the software module to use beam elements. Any other values would cause the software module to use solid elements to represent spot welds. The flag may also be used for providing other information such as the number of solid elements to represent each spot weld. In one embodiment, the possible values for the indicator flag are 1, 4, 8 or 16 for the number of hexahedral elements. In another embodiment, other values may be used for different solid elements (e.g., tetrahedron). Based on the indicator flag404, the software module is able to generate required nodes and solid elements to represent each of the spot welds defined. In order to associate the generated solid elements together to represent one spot weld, the software module groups or assembles a cluster of solid elements representing a single spot weld together in table definition, for example DEFINE_HEX_SPOTWELD_ASSEMBLY_{n}412. In this embodiment, the user specifies the number {n}414of solid elements representing each of the spot welds. An identity of the spot weld416can be specified. A set of n solid elements418is listed to group them together as one cluster to represent the spot weld. It is evident that the model creation of spot welds with solid elements is very tedious. With automated generation of solid elements based on the indicator flag404, the present invention enables the generation of definition412.

FIG. 5shows a flowchart or process500of modeling spot welds in a finite element analysis in accordance with one embodiment of the present invention. The process500is preferably understood in conjunction with the previous figures especiallyFIGS. 3 and 4. The process500starts by receiving an indication flag in a spot weld definition (e.g. a definition for beam element inFIG. 4) at502. The process500then moves to a test504, in which the flag is examined to determine whether beam or solid elements are used to represent spot welds. When the flag indicates beam elements, the process500follows the “Beam” branch to518. The beam element is used to represent spot weld. The process500ends. Otherwise, the flag indicates solid elements at the test504. The process500follows the “Solid” branch to508, in which the number of solid elements for each of the spot welds is determined. In one embodiment, the flag is specified as the number of the solid elements (e.g., an integer such as 1, 4, 8 or 16). It is noted that there may be different number of solid elements representing two different spot welds. Based on the number of solid elements determined in508, the process500generates the number of solid elements and nodes required to represent the spot weld at510. Finally, the process500groups the generated solid elements in a table at514before ending. This is to ensure that the force and moment resultants of the spot weld can be properly computed and assembled based on the information in the table in a file. For example, a file named “swforc’ in LS-DYNA is created to store the force and moment resultants of spot welds.

Although an exemplary embodiment of invention has been disclosed, it will be apparent to those skilled in the art that various changes and modifications may be made to achieve the advantage of the invention. It will be obvious to those skilled in the art that some components may be substituted with another component providing same function. The appended claims cover the present invention.