Impact test report

In actual engineering machinery, many components are often affected by impact loads. In machine design, it is necessary to avoid shock wave loads. However, due to the characteristics of structure or operation, impact loads are difficult to completely avoid. For example, during the expansion stroke of the internal combustion engine, gas explosion pushes the piston and connecting rod, causing impact between the piston and connecting rods. When the train is driving or stopping, the hooks between vehicles also produce impact. In some tool machines, impact loads are used to achieve effects that are difficult to achieve, such as forging hammers, impact, rock drilling machines, etc. In order to understand the performance of materials under impact loads, we must conduct impact experiments.
1. Experimental purpose
Understand the significance of impact experiments and the performance of materials under impact loads
Determine the impact toughness value of low carbon steel and cast iron.
2. Experimental equipment and instruments
Digital display styleImpact testing machine, vernier caliper, etc.
3. Basic Principles
Impact experiment is an experiment to study the resistance of materials to dynamic loads. It is different from static loads. Due to the fast loading speed, the stress in the material suddenly increases, and the deformation speed affects the mechanism properties of the material, so the material has another reaction to dynamic loads. Materials that have good plastic properties under static loads often exhibit brittle properties under impact loads.
In addition, in the impact experiment of metal materials, the impact of certain structural characteristics and working conditions that are not easy to discover during static loads on mechanical properties (such as stress concentration, internal defects of materials, temperature during chemical composition and loading, stress state and heat treatment conditions, etc.), so it has certain significance in process analysis and comparison and scientific research.
IV. Impact test piece
Impact specimens of metal materials commonly used in engineering are generally rectangular specimens with notched grooves. The purpose of making products is to facilitate the disclosure of the impact of various factors on the impact resistance of the material when it is deformed at high speed. And understand whether the specimen is damaged by plastic slip or brittle fracture. However, the shape of the notch and the size of the specimen have a great impact on the impact toughness value of the material. To ensure that the experimental results can be compared, the specimen must be made strictly in accordance with the standards issued by the Ministry of Metallurgical Industry. Therefore, the impact experiment of the measured value is essentially a comparative experiment, and the shape of the impact specimen is shown in the figure.

5. Impact experiment form
Simple beam bending impact experiment
Brachial beam bending impact experiment
Tensile impact experiment
Commonly used in simple beam bending impact experimental engineering
6. Experimental methods and steps
When measuring the size of the specimen, you must measure the size of the specimen at the notch.
First of all, understand the structural principles and operating methods of the pendulum impact testing machine, master the operating procedures of the impact testing machine, and be sure to pay attention to safety.
Adjust the pointer of the impact tester to "zero point" and estimate the required damage energy according to the test piece material. First, empty it and measure the frictional power consumption between the parts.
Put the test piece on the impact tester. The simple beam impact experiment should make the surface without notches facing the side of the pendulum impact. The position of the notches should be between the two supports, so that the notches and the pendulum impact blade should be aligned. Lift the pendulum at the same position as the empty position and open the lock lever. Let the pendulum fall, punch the test piece, and then brake to read out the work consumed when the test piece is punched out. The following formula can calculate the impact toughness value of the material

- The work consumed when slamming the test piece
――The cross-sectional area of ​​the specimen notch
7. Things to note:
Pay special attention to safety during the experiment. It is prohibited to lift the pendulum high and then place the test piece. When the pendulum is raised, the person leaves the range of the pendulum swing. Before putting down the pendulum, check whether anyone has not left yet to avoid danger.
8. Discussion topic
What are the performances of low carbon steel and cast iron under impact?
What is the role of material impact experiments in engineering practice?