Common types of failure analysis

summary

Failure analysis has a strong practical significance in improving product quality, technology development and improvement, product repair and arbitration of failure accidents. It is an activity to simulate and reproduce the failure phenomenon, find out the cause of failure and dig out the failure mechanism according to the failure mode and phenomenon through analysis and verification. Methods are divided into destructive analysis, non-destructive analysis, physical analysis, chemical analysis, etc., and the field of component detection.

Common types of failure analysis

The reason for the high early failure rate is that there are unqualified parts in the product; The reason for the high late failure rate is that the product parts enter the failure period after long-term use. The running in of mechanical products and the aging screening of electronic components are the measures to ensure reliability based on this failure law. Failure is divided into temporary failure and permanent failure, sudden failure and gradual failure according to its engineering meaning, and normal loss failure, essential defect failure, misuse failure and overload failure according to the economic point of view. There are many kinds and states of products, and the forms of failure are also very different. Therefore, it is difficult to define a unified mode for failure analysis. Failure analysis can be divided into complete machine failure analysis and part wreckage failure analysis, and failure analysis can also be conducted according to product development stage, failure situation and analysis purpose. The working procedure of failure analysis is usually divided into clear requirements, investigation and research, failure mechanism analysis and countermeasures. The core of failure analysis is the analysis and Revelation of failure mechanism.

Partial detection methods

1. Non destructive testing (NDT) is also called non-destructive testing. It refers to the measurement of the internal and surface structure, property, state and defect type, property, quantity, shape and position of the test piece by means of physical or chemical methods and modern technology and equipment, on the premise of not damaging or affecting the service performance of the test object and not damaging the internal organization of the test object, and using the changes of thermal, acoustic, optical, electrical and magnetic reactions caused by the abnormal internal structure or defects of the material Size, distribution and its changes.

Non destructive testing methods: eddy current testing (ECT), radiographic testing (RT), ultrasonic testing (UT), magnetic particle testing (MT) and liquid penetrant testing (PT). Other nondestructive testing methods: acoustic emission testing (AE), thermal imaging / infrared (TIR), leakage testing (LT), AC field measurement technology (acfmt), magnetic flux leakage testing (MFL), far field testing (RFT), ultrasonic diffraction time difference method (TOFD), etc.

2. Physical test is the analysis and inspection of the material to determine whether the strength bearing capacity of the material meets the standard. A test conducted to test the ability of a material or structure to withstand forces without damage. The material strength test measures the yield limit, strength limit or fatigue limit of the material. The structural strength test measures the ultimate bearing capacity of the structure, which is not only related to the material strength, but also related to the geometry of the structure, mechanism accessories and external force action forms. According to the test loading methods, the static strength test, dynamic strength test and fatigue strength test are adopted. According to the ambient temperature, it can be divided into normal temperature strength test, hot (high temperature) strength test or cold (low temperature) strength test. The test equipment includes static strength test equipment, dynamic strength test equipment and fatigue strength test equipment.

3. Chemical analysis is an analysis based on the chemical reaction of substances, which is called chemical analysis. Chemical analysis has a long history and is the basis of analytical chemistry, also known as classical analysis. Chemical analysis is absolutely quantitative. The amount of components to be measured is calculated according to the amount of samples, the amount of reaction products or the amount of reagents consumed and the stoichiometric relationship of the reaction. Another important analytical method is instrumental analysis, which is relatively quantitative and estimated according to the standard working curve.

Chemical analysis classification

1. Titration analysis is an analytical method of dropping a standard solution with known accurate concentration into the solution of the substance to be measured until the amount of the added solution substance is completely reacted according to the stoichiometric relationship, and then calculating the content of the substance to be measured according to the concentration of the added standard solution and the consumed volume. Since this measurement method is based on the measurement of solution volume, it is also called volumetric analysis.

According to different reaction types, titration analysis can be divided into:

1. Acid base titration: measure the pH and acid-base content of various acids and bases;

2. Redox titration method: measure substances with redox property;

3. Complexometric titration: measure the content of metal ions;

4. Precipitation titration: measure halogen and silver.

2. Gravimetric analysis is a quantitative measurement method in chemical analysis, which refers to the analysis method with mass as the measurement value. Separate the tested group from other groups and weigh to calculate the content. Accurate to 0.1-0.2%, the measurement error of low content components is large, and it is also called gravimetric method.

Classification and characteristics of gravimetric analysis

1. Precipitation method: it is an important method of gravimetric analysis. This method is to use the reagent and the component to be measured to form a precipitation with very small solubility, and then filter, wash, dry or burn it into a certain composition, then weigh its mass, and then calculate the content of the component to be measured.

2. Gasification method (volatilization method): use the volatilization property of the substance to volatilize the components to be tested in the test by heating or other methods, and then calculate the content of the components according to the reduction of the mass of the sample; Or the content of the component is calculated according to the increase in the mass of the absorbent by using the component released from the absorbent.

3. Electrolysis method: the metal ions to be measured are reduced and precipitated on the electrode by electrolysis method, and then weighed, and the content is obtained according to the added quality requirements of the electrode. Gravimetric analysis is a classical chemical analysis method. It obtains the analysis results through direct weighing. It does not