The present invention relates to a method of analyzing spot welds and more particularly to a method of predicting spot weld failure.
Vehicle design plays a role in determining how a vehicle will perform during an impact event. Namely, the size, shape, and weight of the vehicle—just to name a few—affect the overall performance of the vehicle during an impact event. Further, performance of a particular vehicle during an impact event can be varied as parameters of the impact event are varied. For example, altering the speed and/or physical barrier (i.e., reinforced wall versus offset, honeycomb structure) likewise affects the performance of the vehicle.
Providing an engineer with information relating to how a vehicle may perform during an impact event in the early stages of vehicle development provides information that may be used to alter the design of the vehicle and, thus, its performance during an impact event. While such information is valuable during the early stages of vehicle development, such information is typically unavailable, as physical vehicles are not available for testing. To that end, vehicle manufacturers typically utilize vehicle crash simulation software and other virtual crash simulation devices in an effort to determine how a particular vehicle will perform when subjected to various forces associated with an impact event. Performing simulated impact events may be used during the early stages of vehicle development to aid engineers in designing a vehicle and may be used throughout the vehicle development process to minimize the number of actual vehicle impact tests. Reducing the number of actual vehicle tests reduces the cost associated with vehicle development and expedites the overall vehicle-development process.
Conventional virtual tools that perform vehicle crash simulation typically require numerous inputs to properly correlate a simulated vehicle impact event with actual test data. Such impact simulations work well when test data from actual vehicle tests is available, as correlation between the simulation and the actual tests can be easily performed. For example, conventional virtual tools assume that spot welds of a virtual vehicle model do not fail when performing a simulation. This assumption works well when actual vehicle test data can be used to correlate the results of the vehicle simulation.
While virtual tools are mostly reliable, such tools are less reliable when actual vehicle test data is not available. For example, vehicle impact simulations cannot be verified when performed during the early stages of vehicle development, as actual test data is typically not available for correlation with the simulation. When actual test data is not available for correlation with a simulation, assumptions—such as the assumption with respect to failure of simulated spot welds—may result in an erroneous result. Further, requiring such test data for correlation with a simulated impact event results in conventional virtual tools being complex, costly, and difficult to use.
A method is provided and may include generating by a computer a virtual vehicle model and providing the vehicle model with spot-welds. The method may further include providing data regarding the spot-welds and applying forces by the computer to the spot welds during a simulated impact event of the vehicle model. The computer may analyze each of the spot welds at predetermined time intervals during the simulated impact event and may identify failed spot welds based on the analyzing. The computer may further remove failed spot welds from the vehicle model and may continue to apply the forces to the spot-welds following removal of the failed spot welds.
A method may further include generating by a computer a virtual vehicle model and providing the vehicle model with spot-welds. The computer may determine the nominal shear stress (Ss) at a given load for each of the spot-welds by dividing the applied normal shear load by the product of the weld diameter and the thickness of the smallest sheet meal used in forming the spot weld and may determine the ultimate dynamic shear strength (Ss,dynamic) of each of the spot welds. A first ratio may be determined by dividing the nominal shear stress (Ss) by the ultimate dynamic shear strength (Ss,dynamic) for each of the spot welds. The computer may determine the nominal normal stress (Sn) at a given load for each of the spot welds by dividing the applied normal load by the product of the weld diameter and the thickness of the smallest sheet meal used in forming the spot weld. The computer may further determine the ultimate dynamic normal strength (Sn,dynamic) of each of the spot welds. A second ratio may be determined by dividing the nominal normal stress (Sn) by the ultimate dynamic normal strength (Sn,dynamic) for each of the spot welds. A spot-weld value may be determined for each of the spot welds by a function of the first ratio and the second ratio and a spot-weld failure may be determined if the spot-weld value exceeds one (1).
Further areas of applicability of the present invention will become apparent from the detailed description provided hereinafter. It should be understood that the detailed description and specific examples, while indicating the preferred embodiment of the invention, are intended for purposes of illustration only and are not intended to limit the scope of the invention.
The present invention will become more fully understood from the detailed description and the accompanying drawings, wherein:
The following description of the preferred embodiment(s) is merely exemplary in nature and is in no way intended to limit the invention, its application, or uses.
With particular reference to
The methodology 10 may be performed on each spot weld of a virtual vehicle model and may be performed at predetermined time intervals during a simulated vehicle impact event of the virtual vehicle model. In one configuration, the methodology 10 requires a series of four inputs 18 to determine whether a particular spot weld of the virtual vehicle model will fail during a simulated vehicle impact event. The four inputs 18 may include the weakest material used in forming a spot-welded joint, a weld diameter of a spot weld, the thinnest sheet metal thickness of two or more sheets used to form a spot-welded joint, and the load applied to the spot-welded joint. The inputs 18 may be received by the computer 12 and stored in the memory 16. The processor 14 may perform a dynamic failure criterion 20 and, based on the results of the dynamic failure criterion 20, may output a value at 22. Based on the particular value output by the dynamic failure criterion 20, the computer 12 will determine if and when (i.e., at what time interval) the particular spot weld of the virtual vehicle model will fail, as will be described in greater detail below.
With particular reference to
In addition to receiving information regarding the weakest material used in a welded joint at 24, the computer 12 may also receive information regarding the diameter of a spot weld at 26 and may receive information regarding the thickness of the thinnest sheet metal utilized in forming the spot weld at 28. While the computer 12 is described as receiving information regarding the thickness of the thinnest sheet metal utilized in forming a spot-welded joint, the computer 12 could alternatively receive the thickness of each sheet utilized in forming the spot-welded joint and may compute an average thickness of the sheets for use by the processor 14 in evaluating the particular spot weld. While the processor 14 may utilize the thickness of the thinnest sheet metal utilized or an average of the thicknesses of each sheet utilized in forming a spot-welded joint, the processor 14 will be described hereinafter and shown in the drawings as utilizing the thickness of the thinnest sheet metal at step 28 in determining if and when a spot-welded joint will fail.
The weakest material used in the spot-welded joint, the diameter of the spot weld, and the thickness of the thinnest sheet metal utilized in forming the spot-welded joint may be manually input into the computer 12 at 24, 26, and 28, respectively. The foregoing three parameters can be manually input for each spot weld of a virtual vehicle model when the virtual vehicle model is constructed. While each of the foregoing three parameters may be manually input into the computer 12, the computer 12 could alternatively obtain the weakest material used in each spot-welded joint and the thickness of the thinnest sheet metal utilized in each spot-welded joint of a virtual vehicle model if the virtual vehicle model includes information regarding the type and thickness of each piece of sheet metal used when creating the virtual vehicle model. If the virtual vehicle model includes such information, the processor 14 may obtain the weakest material and thickness of each piece of sheet metal from the virtual vehicle model, thereby obviating the need to manually input the weakest material and thickness of the thinnest sheet metal for each spot-welded joint. Likewise, if the weld diameter for each spot weld of the virtual vehicle model is defined when the virtual vehicle model is created, the processor 14 can likewise obtain the weld diameter directly from the virtual vehicle model, thereby obviating the need to manually input the diameter of each spot weld.
Regardless of how (i.e., manually or directly from the virtual vehicle model) the processor 14 obtains the weakest material used for each spot-welded joint, the weld diameter of each spot-weld, and the thickness of the thinnest sheet metal utilized in each spot-welded joint, the processor 14 may determine the spot weld ultimate static normal strength (Sn,static) and spot weld ultimate static shear strength (Ss,static) for the weakest material at 30. Specifically, the processor 14 may determine the spot weld ultimate static normal strength (Sn,static) by utilizing Equation 1 below and may determine the spot weld ultimate static shear strength (Ss,static) by utilizing Equation 2 below.
In Equation 1, (Sn,1) and (Sn,2) are the spot weld ultimate static normal strength for a first material and a second material, respectively, while (Sut,1) and (Sut,2) are the ultimate tensile strength of the first material and the second material, respectively. Likewise, in Equation 2, (Ss1) and (Ss2) are the spot weld ultimate static shear strength for the first material and the second material, respectively, and (Sut,1) and (Sut,2) are the ultimate tensile strength of the first material and the second material, respectively. The spot weld ultimate static normal strength (Sn,static), spot weld ultimate static shear strength (Ss,static), and ultimate tensile strength (Sut) may be determined based on static test data. For example, the spot weld ultimate static normal strength (Sn,static), spot weld ultimate static shear strength (Ss,static), and ultimate tensile strength (Sut) can be determined based on static test data for a particular material and then can be utilized for different materials based on Equations 3 and 4 below.
As indicated in Equations 3 and 4, the ratio of the spot weld ultimate static normal strength for a first material (Sn,1) to the ultimate strength of the first material (Sut,1) is proportional to the ratio of the spot weld ultimate static normal strength for a second material (Sn,2) to the ultimate strength of the second material (Sut,2). Therefore, the ratio of the spot weld ultimate static normal strength for the first material (Sn,1) to the ultimate strength of the first material (Sut,1) and the ratio of the spot weld ultimate static normal strength of the second material (Sn,2) to the ultimate strength of the second material (Sut,2) are equal and can be represented by a constant (Cn).
As with the spot weld ultimate static normal strength (Sn) of the first material and the second material, the ratio of the spot weld ultimate static shear strength of a first material (Ss,1) to the ultimate strength of the first material (Sut,1) to the ratio of the spot weld ultimate static shear strength of a second material (Ss,2) to the ultimate strength of the second material (Sut,2) are proportional. Therefore, the ratio of the spot weld ultimate static shear strength of the first material (Ss,1) to the ultimate strength of the first material (Sut,1) and the ratio of the spot weld ultimate static shear strength of the second material (Ss,2) to the ultimate strength of the second material (Sut,2) are equal and can be represented by a constant (Cs).
Based on Equations 3 and 4, static test data for a single material may be input into the computer 12. The processor 14 may utilize the static test data for the particular material in determining the spot weld ultimate static normal strength (Sn,static) and spot weld ultimate static shear strength (Ss,static) of a different material, based on the relationships set forth in Equations 3 and 4. Static test data for each material utilized in the virtual vehicle model—including spot weld ultimate static normal strength (Sn,static), spot weld ultimate static shear strength (Ss,static), and ultimate tensile strength (Sut)—is not required by the processor 14. Rather, the processor 14 can rely on the ratios set forth in Equations 3 and 4 in determining the spot weld ultimate static normal strength (Sn,static) and the spot weld ultimate static shear strength (Ss,static) for a spot-welded joint having at least two dissimilar materials.
Once the spot weld ultimate static normal strength (Sn,static) and spot weld ultimate static shear strength (Ss,static) are determined using Equations 1 and 2 above, the processor 14 may determine the spot weld ultimate dynamic normal strength (Sn,dynamic) and spot weld ultimate dynamic shear strength (Ss,dynamic) for the weakest material of a spot-welded joint at 32. Specifically, the processor 14 may determine the spot weld ultimate dynamic normal strength (Sn,dynamic) utilizing the relationship shown in Equation 5 and may determine the spot weld ultimate dynamic shear strength (Ss,dynamic) utilizing the relationship set forth in Equation 6.
As shown in Equations 5 and 6, the spot weld ultimate static normal strength (Sn,static) determined in Equation 1 is utilized in Equation 5, while the spot weld ultimate static shear strength (Ss,static) determined in Equation 2 is utilized in Equation 6. Other than the spot weld ultimate static normal strength (Sn,static) and spot weld ultimate static shear strength (Ss,static), the only other input required by Equations 5 and 6 is the load rate {dot over (P)}, which is defined as the change in load divided by the change in time.
The spot weld ultimate dynamic normal strength (Sn,dynamic) and spot weld ultimate dynamic shear strength (Ss,dynamic) may be utilized by the processor 14 when performing the dynamic failure criterion 20 (
In Equation 7, the spot weld ultimate dynamic normal strength (Sn,dynamic) and spot weld ultimate dynamic shear strength (Ss,dynamic) determined in Equations 5 and 6, respectively, are utilized by Equation 7 to determine if and when a particular spot weld will fail under a given load. The nominal shear stress (Ss) and nominal normal stress (Sn) may be determined by Equations 8 and 9, respectively, where Pn is the spot weld normal stress, Ps is the spot weld shear stress, D is the weld diameter, and t is the thickness of the thinnest sheet metal utilized in the spot-welded joint.
The exponent data (δ) may be determined experimentally by subjecting a spot weld to loads at various angles and generating a failure curve/surface. The failure curve/surface may be plotted on a relationship of the applied nominal normal stress (Sn) versus the applied nominal shear stress (Ss), whereby the exponent (δ) is defined by the shape of the failure curve/surface. The exponent (δ) is a value generally between one (1) and two (2), as an exponent (δ) equal to one (1) would result in a failure curve being substantially straight while an exponent (δ) having a value of two (2) would result in a failure curve forming one-quarter of a circle. Providing the exponent term with a value between one (1) and two (2) provides the shape of the failure curve somewhere between a straight line and a curve representing one-quarter of a circle.
Once the processor 14 determines the nominal normal stress (Sn) and nominal shear stress (Ss), the processor 14 may perform the dynamic failure criterion 20 by utilizing the relationship set forth in Equation 7. Applying the relationship set forth in Equation 7 allows the processor 14 to determine whether a particular spot weld will fail at 36. If the value (V) output by Equation 7, for example, is less than or equal to one (1), the processor 14 determines that the weld does not fail at 38. If, on the other hand, the value determined by the processor 14 utilizing Equation 7 is not less than or equal to one (1), the processor 14 determines that the weld fails at 40.
While the foregoing Equations 1-9 provide the basis for the processor 14 in determining whether a spot weld will fail and, if so, when the spot weld will fail,
An exemplary curve is shown in
With particular reference to
As described above, the methodology 10 may require input of the weakest material used in forming each spot weld, the weld diameter of each spot weld, and the thickness of the thinnest sheet metal used in forming each spot weld. The foregoing inputs may be provided to the memory 16 of the computer 12 at 44. While the foregoing inputs may be provided to the computer 12 by way of manually inputting each input, the foregoing inputs could alternatively be retrieved by the computer 12 from the virtual vehicle model, as described above.
Once each spot weld of the virtual vehicle is identified and the parameters set forth at step 44 are provided to the computer 12, the computer 12 may begin a simulated vehicle impact event. Specifically, the processor 14 may apply simulated forces to each spot weld of the virtual vehicle model at predetermined time intervals (n) during the simulated vehicle impact event at 46. During the simulated vehicle impact event, the processor 14 may apply the dynamic failure criterion 20 to each spot weld at each predetermined time interval (n) at 48.
As described above, applying the dynamic failure criterion 20 to each spot weld allows the dynamic failure criterion 20 to identify failed welds if the result of the dynamic failure criterion 20 exceeds one (1). Therefore, the processor 14 may utilize the dynamic failure criterion 20 to identify spot weld failures at 50 and may remove failed welds from the virtual vehicle model at 52. The processor 14 may continue the simulated vehicle impact event at the next predetermined time interval (n+1) at 54 following removal of the failed welds. The processor 14 may continue to perform the methodology 10 on each spot weld at each predetermined time interval (n) and may continue to remove failed welds in an effort to provide a simulated vehicle impact event that correlates well with an actual impact event.
Removing the failed welds allows the simulated vehicle impact event to correlate well with an actual vehicle test, as removing failed welds allows the forces applied at 46 to be transferred to other neighboring spot-welded joints or other load-bearing elements/components of the virtual vehicle model. The virtual vehicle model can then be compared to an actual vehicle test by comparing the performance of each spot-welded joint at each predetermined time interval (n) of the virtual vehicle model. If the simulated vehicle impact event correlates well with an actual vehicle test, a particular spot weld should fail at approximately the same time interval (n) in both the simulated vehicle impact event and in the actual vehicle test. Namely, the result of the dynamic failure criterion 20 should exceed one (1) within the same predetermined time interval (n) that the spot weld fails in the actual vehicle test.
For example, as shown in
The description of the invention is merely exemplary in nature and, thus, variations that do not depart from the gist of the invention are intended to be within the scope of the invention. Such variations are not to be regarded as a departure from the spirit and scope of the invention.
This application is a continuation-in-part of U.S. patent application Ser. No. 13/273,536 filed on Oct. 14, 2011. The entire disclosure of the above application is incorporated herein by reference.
Number | Date | Country | |
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Parent | 13273536 | Oct 2011 | US |
Child | 13334701 | US |