Forklift frame structure service life prediction method

Abstract

The invention discloses a method for predicting the service life of a forklift frame structure, a frame serves as a forklift main stress component, other systems are all installed on the frame, the method obtains a stress-time history curve of the position, most prone to fatigue failure, of the forklift frame under one operation cycle through stress testing of the forklift frame under the specific operation working condition, and the service life of the forklift frame structure is predicted according to the stress-time history curve of the position, most prone to fatigue failure, of the forklift frame. Through data processing and rain flow counting, stress-time history data of a position most prone to fatigue failure are counted as stress amplitude, average stress and corresponding cycle times in a time period, and accumulated damage in one operation cycle is calculated through an S-N curve of a material, an average stress correction formula and a two-dimensional stress spectrum. Therefore, the fatigue life of the forklift frame is obtained, a life threshold value is set, and early warning is carried out on the life state of the forklift frame.

Description

Technical Field

[0001] The present invention relates to the technical field of forklifts, and in particular to a method for predicting the life of a forklift structure. Background Art

[0002] Forklifts are currently the most commonly used tool for material handling and loading and unloading. As the main load-bearing component of forklifts, forklift frames have repeatedly suffered from fatigue failure. As a load-bearing structure, the failure of metal structures not only makes forklifts lose their functions, but also brings great harm to production and personal safety. Therefore, a fatigue life prediction method for forklift frames is urgently needed. Summary of the invention

[0003] Purpose: The present invention provides a method for predicting the life of a forklift frame structure. The frame is the main load-bearing component of the forklift, and the other systems are installed on the frame. The method obtains the stress-time history curve of the position of the forklift frame most prone to fatigue failure under one operating cycle by stress testing the forklift frame under specific operating conditions. Through data processing and rain flow counting, the stress-time history data of the position most prone to fatigue failure are statistically analyzed as the stress amplitude, average stress and corresponding number of cycles within a time period. Through the SN curve of the material, the average stress correction formula and the two-dimensional stress spectrum, the cumulative damage within one operating cycle is calculated to obtain the fatigue life of the forklift frame.

[0004] Technical solution: To solve the above technical problems, the technical solution adopted by the present invention is: a method for predicting the life of a forklift frame structure, which determines the fatigue failure positions of the frame structure through finite element analysis results and previous failure positions, and these fatigue failure positions are used as stress measurement points;

[0005] Select specific operating conditions, perform strain gauge patch testing on stress measurement points, and collect strain-time history data for one operating cycle; select the commonly used specific operating conditions as the operating conditions when the forklift is at maximum load;

[0006] The collected strain data is converted into stress to obtain the stress-time history curve of one operation cycle. The frame structure is in the material elastic stage. The conversion formula is:

[0007] σ=Eε

[0008] Where σ is stress, E is the elastic modulus of the material, and ε is the measured strain data.

[0009] Data preprocessing is performed on the stress-time history data of each measuring point, including removal of abnormal points, compression of equivalent points, etc.;

[0010] Through the rain flow counting method, mathematical statistics are performed on the processed stress-time history data to obtain the two-dimensional stress spectrum of each measuring point within one operation cycle, that is, the table of stress amplitude, average stress and corresponding cycle number within the test time period;

[0011] Determine the SN curve of the material at the fatigue failure location. The stress ratio of the material SN curve is -1, that is, a symmetrical cyclic stress curve.

[0012] The average stress at the fatigue failure position of the forklift frame structure is generally not 0, and the average stress correction is required to calculate the fatigue damage. The correction formula is:

[0013]

[0014] Where σ -1 is the fatigue strength when the stress ratio is -1, σ m is the mean stress, σ b is the ultimate strength of the material;

[0015] According to the linear fatigue cumulative damage theory, a certain stress amplitude level σ i The damage caused is expressed as n i / N i , calculate the damage of k fatigue levels at each position, and the damage calculation formula is

[0016]

[0017] n i —N is the number of stress cycles at the i-th stress level; i —Number of stress cycles to failure at the i-th stress level;

[0018] The cumulative damage in one hour is calculated from the number of operating cycles L in one hour. The formula is:

[0019] D H =LD

[0020] D H Fatigue damage within 1 hour;

[0021] Based on the structural fatigue damage within 1 hour, the predicted service life of the forklift frame structure is in hours N. H The calculation formula is

[0022] N H =1 / D H .

[0023] The service life of the forklift structure is set to 0.7 times the predicted service life hours as the life threshold, and an early warning is issued for forklifts approaching this value.

[0024] Beneficial effects: This method selects specific operating conditions, performs strain gauge patch tests on stress measurement points, and collects strain-time history data of an operating cycle. It can provide more accurate data for the method, making its calculation results more accurate, and average stress correction in the method can further improve the calculation accuracy, making its calculation results more accurate. The warning time of this method and the fatigue warning time required by the actual forklift frame structure have a smaller error. This life prediction method can predict the life of the forklift frame and warn of its safety status, reduce the risk of accidents, and improve the safety of forklift operations. BRIEF DESCRIPTION OF THE DRAWINGS

[0025] Figure 1 It is a technical flow chart of the forklift frame structure life prediction method;

[0026] Figure 2 The stress-time history curve of the fatigue failure position of the forklift frame;

[0027] Figure 3 The two-dimensional stress spectrum of the fatigue failure position of the vehicle frame;

[0028] Figure 4 This is the mean stress correction diagram. DETAILED DESCRIPTION

[0029] In order to make the purpose, technical solution and advantages of the present invention more clear, the present invention is further described in detail below through the accompanying drawings and embodiments. However, it should be understood that the specific embodiments described herein are only used to explain the present invention and are not intended to limit the scope of the present invention.

[0030] Unless otherwise defined, all technical and scientific terms used herein have the same meaning as commonly understood by technicians in the technical field to which the present invention belongs. The terms used in the specification of the present invention are only for the purpose of describing specific embodiments and are not intended to limit the present invention.

[0031] like Figure 1 As shown, a forklift frame structure life prediction method includes:

[0032] Firstly, based on the finite element analysis results of the forklift frame structure and the previous failure positions, the fatigue failure positions of the frame structure are determined, and these fatigue failure positions are used as stress measurement points;

[0033] Select commonly used specific working conditions, perform strain gauge patch tests on stress measuring points, collect complete strain-time history data within one working cycle through the strain-stress conversion formula, and select commonly used specific working conditions as the working conditions when the forklift is at maximum load;

[0034] The collected strain data is converted into stress to obtain the stress-time history curve of one working cycle, such as Figure 2 As shown, the frame structure is in the material elastic stage, and the conversion formula is:

[0035] σ=Eε

[0036] Where σ is stress, E is the elastic modulus of the material, and ε is the measured strain data.

[0037] Data preprocessing is performed on the stress-time history data of each measuring point, including removal of abnormal points, compression of equivalent points, etc.;

[0038] Through the rain flow counting method, mathematical statistics are performed on the processed stress-time history data to obtain the two-dimensional stress spectrum of each measuring point within one operation cycle time, that is, the table of stress amplitude, average stress and corresponding cycle number within the test time period, such as Figure 3 As shown;

[0039] Determine the SN curve of the material at the fatigue failure location. The stress ratio of the material SN curve is -1, that is, a symmetrical cyclic stress curve.

[0040] Based on the average stress of the two-dimensional stress spectrum and the average stress correction formula, the average stress correction is performed, such as Figure 4 As shown;

[0041] The fatigue cumulative damage of each fatigue failure-prone position is calculated through the linear fatigue cumulative damage theory; that is, the SN curve of the material at the fatigue failure-prone position is determined, and the stress ratio of the material SN curve is -1, that is, a symmetrical cyclic stress curve;

[0042] The average stress at the fatigue failure position of the forklift frame structure is generally not 0, and the average stress correction is required to calculate the fatigue damage. The correction formula is:

[0043]

[0044] Where σ -1 is the fatigue strength when the stress ratio is -1, σ m is the mean stress, σ b is the ultimate strength of the material;

[0045] According to the linear fatigue cumulative damage theory, a certain stress amplitude level σ i The damage caused is expressed as n i / N i , calculate the damage of k fatigue levels at each position, and the damage calculation formula is

[0046]

[0047] n i—N is the number of stress cycles at the i-th stress level; i —The number of stress cycles required to reach failure at the i-th stress level.

[0048] The cumulative damage in one hour is calculated from the number of operating cycles in one hour and the fatigue damage of a single cycle. That is, the cumulative damage in one hour is calculated from the number of operating cycles in one hour, L. The formula is:

[0049] D H =LD

[0050] D H Fatigue damage within 1 hour;

[0051] Based on the structural fatigue damage within 1 hour, the predicted service life hours of the forklift structure are predicted, that is, based on the structural fatigue damage within 1 hour, the predicted service life hours of the forklift frame structure are N H The calculation formula is

[0052] N H =1 / D H .

[0053] A threshold for predicted life hours is set, and an early warning is issued when the service time approaches the threshold, prompting the user to pay special attention to the frame status; that is, the service life of the forklift structure is set to 0.7 times the predicted life hours as the life threshold, and an early warning is issued for forklifts approaching this value.

[0054] The above description is only a preferred embodiment of the present invention and is not intended to limit the present invention. Any modification, equivalent substitution or improvement made within the spirit and principle of the present invention should be included in the protection scope of the present invention.

Claims

1. A method for predicting the life of a forklift frame structure, characterized in that: The steps include: According to the finite element analysis results of the forklift frame structure and the previous failure positions, the fatigue failure positions of the frame structure are determined, and these fatigue failure positions are used as stress measurement points; Select common specific working conditions, perform strain gauge patch testing on the stress measurement points of the forklift frame structure, and collect complete stress-time history data within one working cycle; Preprocess the stress-time history data of each measuring point; The rain flow counting method is used to count the preprocessed data in cycles to obtain the two-dimensional stress spectrum of each measuring point within the test time period; Based on the two-dimensional stress spectrum, the cumulative damage within one operation cycle is calculated through the material's SN curve and the average stress correction formula; Based on the number of cycles within 1 hour, calculate the structural fatigue damage in 1 hour; based on the structural fatigue damage in 1 hour, predict the number of hours of structural life; set the frame structure life threshold and issue an early warning on the life status of the forklift frame.

2. A forklift frame structure life prediction method according to claim 1, characterized in that: The commonly used specific operating conditions are selected as the operating conditions when the forklift is at maximum load.

3. A forklift frame structure life prediction method according to claim 1, characterized in that: The collected strain data is converted into stress through the strain-stress conversion formula to obtain the stress-time history curve of one operation cycle. The frame structure is in the material elastic stage, and the conversion formula is: σ=Eε Where σ is stress, E is the elastic modulus of the material, and ε is the measured strain data.

4. A forklift frame structure life prediction method according to claim 1, characterized in that: Through the rain flow counting method, mathematical statistics are performed on the processed stress-time history data to obtain the two-dimensional stress spectrum of each measuring point within one operation cycle, that is, a table of stress amplitude, average stress and corresponding number of cycles within the test time period.

5. A forklift frame structure life prediction method according to claim 1, characterized in that: Based on the two-dimensional stress spectrum, the cumulative damage within one operation cycle is calculated through the SN curve of the material and the average stress correction formula. The specific steps are: determine the SN curve of the material at the fatigue failure position. The stress ratio of the material SN curve is -1, that is, a symmetrical cyclic stress curve; The average stress at the fatigue failure position of the forklift frame structure is generally not 0, and the average stress correction is required to calculate the fatigue damage. The correction formula is: Where σ i1 is the fatigue strength when the stress ratio is -1, σ m is the mean stress, σ b is the ultimate strength of the material; According to the linear fatigue cumulative damage theory, a certain stress amplitude level σ i The damage caused is expressed as n i / N i , calculate the damage of k fatigue levels at each position, and the damage calculation formula is n i —N is the number of stress cycles at the i-th stress level; i —The number of stress cycles required to reach failure at the i-th stress level.

6. A forklift frame structure life prediction method according to claim 1, characterized in that: According to the number of cycles within 1 hour, the structural fatigue damage within 1 hour is calculated; according to the structural fatigue damage within 1 hour, the structural life hours are predicted; the frame structure life threshold is set to warn the forklift frame life status; specifically: the cumulative damage within 1 hour is calculated based on the number of operation cycles L within 1 hour, and the formula is D H =LD D H Fatigue damage within 1 hour; Based on the structural fatigue damage within 1 hour, the predicted service life of the forklift frame structure is in hours N. H The calculation formula is N H =1 / D H .

7. A forklift frame structure life prediction method according to claim 6, characterized in that: The service life of the forklift structure is set to 0.7 times the predicted service life hours as the life threshold, and an early warning is issued for forklifts approaching this value.

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