Small bolts continue to test equipment development and new research strategy
The pre-tightening nut applies a pre-tightening force to the BOLT coupling portion by rotating the pre-tightening nut. The loading portion consists of a tension sensor, a loading SCREW and a loading nut. A working load is applied to the bolted joint by rotating the loading nut. The size of the working load can be measured by tension sensors and instruments. The measuring section consists of strain gauges attached to the part to be tested, a high-precision measuring amplifier and a single-chip microcomputer system. It can measure the working load and measure the deformation of bolts and sleeves with high measurement accuracy.
Content (1) Deformation coordination experiment capable of opening bolts In the bolt connection, the bolts are subjected to tensile force and tensile deformation; the connected parts are subjected to pressure and compressive deformation is generated. The increment of the bolt elongation deformation is equal to the amount of recovery of the compression deformation of the joint. Through the calculation, analysis and drawing of the experimental data, the deformation coordination relationship in the bolt connection can be proved.
(2) It is possible to open the relationship between the total tensile force of the bolt and the working load and the residual preload of the coupled member, and the relationship between the preload and the working load and the relative stiffness of the bolt. Through the calculation, analysis and drawing of the experimental data, the above conclusion can be proved, thereby correcting the wrong view that the total pulling force of the bolt is equal to the pre-tightening force plus the working load.
(3) The effect of pre-tightening force on the bolt stress amplitude can be established. Under the condition that the working load is the same, the bolt and the connected member have the same stiffness, the pre-tightening force is increased within the allowable tensile stress range of the bolt. The stress amplitude is constant, that is, the pre-tightening force has no effect on the stress amplitude of the bolt. However, appropriately increasing the pre-tightening force will increase the total tension of the bolt and the remaining pre-tightening force of the coupled member, thereby improving the fatigue strength of the bolt and improving the reliability and tightness of the bolt connection, thus improving the bolt connection. Strength of. This is an important reason why the bolt preload stress is sometimes as high as (0.70.8) s.
(4) The effect of the relative stiffness on the bolt stress amplitude can be established. Under the condition that the working load and the preload force are kept constant, the relative rigidity of the bolt is reduced, that is, the rigidity of the bolt is reduced or the rigidity of the coupled member is increased. The purpose of reducing the bolt stress amplitude can be achieved. However, at this time, the residual pre-tightening force is also reduced, thereby reducing the tightness of the joint and adversely affecting the reliability of the bolt connection. Therefore, the pre-tightening force should be appropriately increased to keep the residual pre-tightening force unchanged. Under the premise that the maximum stress of the bolt and the residual pre-tightening force remain unchanged, the stress amplitude is reduced, and the strength and reliability of the bolt connection are improved.
The teaching mode experiment class is conducted in an autonomous and open teaching mode. The experimental instructor arranges the experimental tasks to let the students clarify the purpose of the experiment and the experimental content. Students develop their own experimental protocols and experimental procedures to familiarize themselves with the performance of the experimental equipment and the use of the test equipment. After the experimental plan and experimental steps formulated by the students are approved by the instructor, the students can install and debug the experimental device. The instructor will inspect the experimental device and the test instrument. After the approval, the student will perform the experimental operation. Students do their own experiments, record data, write experimental analysis reports, and calculate, analyze and draw experimental curves for experimental data, and draw correct conclusions; if the experiment fails, the reasons for the experimental failure should be carefully summarized, and then the correct Experiment and experimental steps, re-run the experiment. The student prepares the experimental analysis report and submits it to the experimental instructor for review. The experimental results given by the experimental instructor are registered and archived by the teaching authority.
The effect of relative stiffness on bolt stress amplitude 4 Practical experience (1) In the experiment, students are the main body, and all the experimental processes are completed independently by the students, giving full play to the students' subjective initiative and cultivating students' pioneering spirit, hands-on ability and independent work. Ability to strengthen students' engineering practice awareness, so that students are subject to experimental formal training independently of experimental subjects and independent ability to solve practical problems in engineering. Throughout the experiment, the experimental instructor only plays a role of auxiliary guidance and orientation control. It is mainly responsible for checking and supervising the students' staged work, answering the difficult problems in the students' experimental process, and reviewing the experiments formulated by the students. Whether the program and experimental steps are feasible, the experimental analysis report and so on.
(2) The degree of automation of the experimental device should be gradually opened from low to high. Students should not be exposed to the more automated experimental equipment from the beginning, otherwise the students will have less chance of exercising. Experimental teaching not only pays attention to the experimental results, but also pays attention to the experimental process, so that students can truly learn the knowledge. Previously, the experimental equipment we developed was equipped with advanced computer detection and processing systems. Students often focused their attention on the computer, and paid little attention to the principle, structure, testing methods, experimental methods and procedures of the experimental machine. Finished, but the results are minimal. To this end, we used a single-chip microcomputer detection system to replace the microcomputer, and only provided the raw data of the test parameters to the students. The students manually calculated, analyzed and plotted the experimental data. The teaching effect was very good, and the experimental students and students were obtained. Affirmation of the teacher.
(3) Because the students' ability is uneven, sometimes an experiment can be done 23 times. In this way, students will spend more time experimenting, and the guidance time of the experimental instructors will be extended accordingly. The instructors and students are more difficult. It is gratifying that students have the opportunity to exercise and the knowledge they have acquired. increase. It is conceivable that if all the experimental teaching is carried out according to this model, the students' practical ability, innovative ability and independent working ability will be greatly improved. This model of experimental teaching is necessary to promote the application nationwide.
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