types of testing

Types of Testing: there are two main types of tests:
1. Destructive testing
2. Nondestructive testing
Nondestructive Testing
In certain applications, the evaluation of engineering materials or structures without impairing their properties is very important, such as the quality control of the products, failure analysis or prevention of the engineered systems in service. This kind of evaluations can be carried out with non destructive test (NDT) methods. It is possible to inspect and/or measure the materials or structures without destroying their surface texture, product integrity and future usefulness. These methods can be performed on metals, plastics, ceramics, composites, cermet, and coatings in order to detect cracks, internal voids, surface cavities, incomplete defective welds and any type of flaw that could lead to premature failure.
A general definition of nondestructive testing (NDT) is an examination, test, or evolution performed on any type of test object without changing or altering that object in any way, that can provide useful information regarding the condition of the object being examined, approved procedures are followed, and the examinations are conducted by qualified personnel in order to determine the absence or presence of conditions or discontinuities that may have an effect on the usefulness or serviceability of that object. Nondestructive tests may also be conducted to measure other test object characteristics, such as size; dimension; structure, including alloy content, hardness, grain size, etc. Nondestructive examination (NDE), nondestructive inspection (NDI), and nondestructive evaluation (NDE) are also expressions commonly used to describe this technology.
Although NDT cannot guarantee that failures will not occur, it plays a significant role in minimizing the possibilities of failure. Other variables, such as inadequate design and improper application of the object, may contribute to failure even when NDT is appropriately applied.Nondestructive testing, in fact, can be considered as an extension of the human senses, often through the use of electronic instrumentation and
other unique equipment. It is possible to increase the sensitivity and
application of the human senses when used in conjunction with these
instruments and equipment. On the other hand, the misuse or improper
application of a nondestructive test can cause catastrophic results. If the
test is not properly conducted or if the interpretation of the results is
incorrect, disastrous results can occur. It is essential that the proper
nondestructive test method and technique be employed by qualified
personnel, in order to minimize these problems. In industry, nondestructive
testing can do so much more. It can effectively be used for the:
1. Examination of raw materials prior to processing
2. Evaluation of materials during processing as a means of process
control
3. Examination of finished products
4. Evaluation of products and structures once they have been put into
service
Some types of non-destructive methods
Visual inspection:
VI is particularly effective detecting macroscopic flaws, such as poor
welds, VI is also suitable for detecting flaws in composite structures and
piping of all types, poor fits, wrong dimensions, improper surface finish,
delamination in coatings, large cracks, cavities
Radiography
Detecting cracks, however this method is less popular because of the
hazards of handling radioactive materials
Nondestructive testing, in fact, is a process that is performed on a daily basis by the average individual, who is not aware that it is taking place.
The human body has been described as one of the most unique nondestructive testing instruments ever created. all the human senses, the sense of sight provides us with the most versatile and unique nondestructive testing approach. When one considers the wide application of the sense of sight and the ultimate information that can be determined by mere visual observation, it becomes quite apparent that visual testing (VT) is a very widely used form of nondestructive testing.