Understanding the requirements for high tensile fasteners we are undertake all and complete testing requirements under mechanical testing. Mechanical testing is a process that is used to determine the mechanical properties of a material . It can be used to evaluate a material independent of its geometry and also at defined geometrical conditions.
Fastener testing allows you to determine the mechanical properties of externally and internally threaded fasteners, washers, direct tension indicators, and rivets. Testing may consist of a machined specimen or a full-size product. Fastener testing is not applicable to all. The head design, shank thickness, and product length can determine if the testing is required of the product.
Common Types of Mechanical Testing
The process starts with a review of the drawing or part specification to identify appropriate test methods, which can include:
Model generation and validation
When it comes to streamlining the design process, solid modeling of components and assemblies, along with Finite Element Analysis (FEA), are excellent tools for engineers. Often the purpose of mechanical testing is to generate the data required by these FEA programs to generate the initial component models. That being said, FEA models do not guarantee accurate results, so the most practical approach is to:
- Develop a robust model from the materials testing data for the material
- Perform FEA to determine theoretical stress levels and locations
- Use product qualification testing or materials testing on component cut-ups (First Article Inspection) to validate the FEA model.
Since testing provides empirical data, it can be used to go back then and refine the FEA model. Once this step has been achieved, making design modifications in the model is much easier and more reliable without the added time and cost of numerous prototype and test iterations.
- Model : UTE 60
- Make : FIE, India
- Model : UTE 200
- Make : FIE, India
A tensile test applies tensile (pulling) force to a material and measures the specimen's response to the stress. By doing this, tensile tests determine how strong a material is and how much it can elongate.
A good quality bolt is the lifeline of any project or equipment, if the bolting’s are of good quality they will give extra life to the application and where it is used. We have in house testing facility for all kinds destructive and non-destructive testing which are required for testing bolts and nuts. We also follow our own QAP or customers QAP.
We have inhouse Electronic Universal Testing Machine UTE 600 KN & UTE 2000 KN Tensile testing make of FIE. We can break a bolt up to M80 mm with extensometer. Electronically controlled 60 Ton / 600 KN & 200 Ton / 2000 KN load capacity, it is capable to check the ultimate tensile strength, yield strength, reduction in area ratio and give digital outputs for easy study of behaviour of materials, we also have a extensometer to check proof stress at 0.2% offset.
- Yield Strength
- Ultimate Tensile Strength (UTS)
- Strain Hardening
- Modulus of Elasticity
- Proof Load
Chemical analysis is also essential for both material and product manufacturers as it identifies the contents and quality of materials used in manufacturing and product development. During the early stages of the product
development process, it is essential to verify materials to avoid any in-service failures.
We have in house Spectro analytical instruments, employing optical emission (stationary and mobile Arc/Spark OES technology, used for the elemental analysis / Chemical properties of materials. We use Spectro test for
cross verification of Raw material elements. And we have all records of material more than 10 years.
Hardness testing is required after production and also where heat treating is needed to verify conformance. Like tensile testing, this is a speedy and inexpensive testing option and does not usually require the final part to undergo destructive testing.
a) Rockwell Hardness Test
b) Brinell Hardness Test
The Rockwell hardness test evaluates the hardness of a material by measuring the permanent depth of indentation due to an applied concentrated load. The higher the number on the Rockwell hardness scale, the harder the material. The test is conducted by applying a minor force of 10 Kg using a diamond cone or a steel ball indenter on the surface of the material. The depth of indentation from this preliminary load is recorded and used as a reference point.
A specified major load is then applied for a specified dwell time, further indenting the test specimen. The difference between the reference position and the depth of indentation due to the major load is calculated and recorded as the permanent depth of indentation.
The Rockwell hardness is calculated using the following formula:
Rockwell Hardness, HRC = [0.2 – permanent depth of indentation (mm)] x 500
The Rockwell hardness test was developed to be less destructive and cheaper than the Brinell test. Measuring hardness using differential depths helps to eliminate errors due to surface imperfections.
c) Vickers Hardness Test
The Brinell hardness test entails measuring the diameter of indentation caused by a constant concentrated force applied by a steel or carbide spherical indenter on a test specimen. The steel ball indenter is first placed in contact with the material before a constant force is applied and maintained for a 10 to 15 second duration, known as the dwell time. After the dwell time is completed, the spherical indenter is removed, leaving a round-shaped indent on the sample.
The Brinell hardness is calculated using the following formula:
Brinell Hardness, HB = Applied test force in kilogram-force (kgf) ÷ Surface area of indentation (mm2)
This hardness test method makes the widest and deepest indentation of the 5 test methods mentioned in this article, allowing the test to be conducted over a larger surface area of the specimen. This provides test averages of hardness over a wider surface area of material, which has the advantage of taking into account surface and grain irregularities on the metal.
d) Impact Testing
The Vickers hardness test involves the use a 4-sided square-based pyramid indenter, with a precisely defined constant force on the test specimen to evaluate the surface area of the indentation. The specimen is first lifted until it comes into contact with the indenter. The test force is then applied by the indenter to the test specimen, slowly increasing until it reaches its specified value. This force is then held for the appropriate dwell time and the surface area of the diamond or square shaped indentation is calculated.
The Vickers hardness of the material is then found using the following formula:
Vickers Hardness, HV = Applied test force in kilogram-force (kgf) ÷ Surface area of indentation (mm2) or, HK = 1.854 x (F/D2)
By making use of a diamond-shaped indenter as opposed to a sphere (such as in the Brinell and Rockwell hardness tests), the Vickers hardness test can be done using less force and can achieve a higher level of accuracy. By magnifying the surface of the test metal, the test can be used to target microstructural compositions such as martensite or bainite. Because the Vickers hardness test requires the use of optical and measuring equipment and material preparation, the cost tends to be higher than others hardness tests and can also take a longer time to complete compared to the Rockwell test.
e) Micro Vickers hardness test
The impact test is a method for evaluating the toughness, impact strength and notch sensitivity of engineering materials.
Engineers test the ability of a material to withstand impact to predict its behavior under actual conditions. Many materials fail suddenly under impact, at flaws/cracks or notches. The most common impact tests use a swinging pendulum to strike a notched bar; heights before and after impact are used to compute the energy required to fracture the bar. In the Charpy test, the test piece is held horizontally between two vertical bars. In the Izod test, the specimen stands erect, like a fence post.
The notched test specimen is broken by the impact of a heavy pendulum or hammer, falling at a predetermined velocity through a fixed distance. The quantity usually measured is the energy absorbed in breaking the specimen in a single blow, as in the Charpy impact test and Izod impact test.
Impact tests are also performed by subjecting specimens to multiple blows of increasing intensity, as in the drop ball impact test and the repeated blow impact test. Impact resilience and scleroscope hardness are determined in non-destructive impact tests.
The impact resistance of a part is, in many applications, a critical measure of its service life. More importantly, it affects product safety and liability.
Micro Vickers hardness tests as per HV 0,3 is carried out in accordance to ISO 898-1:2013, this test is popularly done to ascertain the exact depth of carburization or decarburization in a fastener. The tests are performed on the threaded area of the bolt or nut and cut according to standard and measured to ascertain the level of decarburization or carburization during heat treatment process.