Destructive Testing

In destructive testing, tests are carried out to the specimen's failure, in order to understand a specimen's structural performance or material behaviour under different loads. These tests are generally much easier to carry out, yield more information, and are easier to interpret than nondestructive testing.

Destructive testing is most suitable, and economic, for objects which will be mass produced, as the cost of destroying a small number of specimens is negligible. It is usually not economic to do destructive testing where only one or very few items are to be produced (for example, in the case of a building).

Some types of destructive testing:

• Stress tests
• Crash tests
• Hardness tests
• Metallographic tests

destructive testing mechanical testing

Bend testing is a type of destructive testing of weldment.

Metal Fabrication Tools

Metal fabrication tools are generally used in fabrication industrial shops in order to shape, cut and assemble large sheets of metal to be used on construction projects. There are many types of metal fabrication tools including drill presses and tube bending machines. Drilling machines and belt drive bench lathes are also used to punch holes into sheet metal and to level out metal works on a regular basis.

Metal fabrication tools are used in order to bend heavy pipe materials

Vertical/Horizontal Belt Grinder

Designed to grind down and level out heavy sheet metal sections for fabrication, the vertical/horizontal belt grinder is powered by a 220-volt electric motor and features a wide sanding belt that is applied to the surface of the metal sheet. Containing two variable speed selections, the vertical/horizontal belt grinder is secured down onto a hard table-top surface and the metal fabricator lays down the piece of metal underneath this tool's sanding belt in order to begin the grinding process.

Hand Punches

Averaging just over 4 inches in total length, the hand punches tool is very portable and is designed to fit into almost any toolbox. Allowing a metal fabricator to quickly punch 1/2 inch to 1-inch holes into aluminum, metal, copper and light steel sheet panels, the hand punches tool is made out of hard metal and resembles a typical house wrench in overall design. Outfitted with easy to grip handles on one end and featuring a wrench-like jaw on the other, workers can grip the handle and bring the jaws of this tool down onto the metal in order to punch the holes.

Tubing Bender

Built for metal fabricators in order to bend 1/2-inch and 2-inch metal and copper pipes, the tubing bender tool stands upright and features a wide metal base section to hold it up. Made out of a very hard steel material, the tubing bender contains a ratcheting arm that the fabricator inserts the pipe into and then retracts the pipe material by pushing on the other end of the ratcheting arm until the pipe is bent correctly.

Shrinker and Stretcher

When a metal fabricator needs to stretch out a piece of metal or a section of steel material, the shrinker and stretcher tool is used. Averaging around 44 inches in height and containing a width of just over 6 inches, the shrinker and stretcher tool features a 6-inch jaw at the top of this upright tool. The fabricator lays the metal into this jaw and then presses down on it by using its attached handle to either stretch out the metal by pulling on the metal outwardly or to shrink it by pushing the metal into the jaw section.

WHAT is Metal Fabrication ?

Metal fabrication is defined through the construction of machines and equipment from raw materials that have been designed, cut, burned, shaped, machined and welded to form the final product. In most cases, metal-fabrication shops focus on preparing metal for welding and assembly.

Engineering Drawings

Engineering drawings are used to bid for metal-fabrication contracts. When a contract is awarded based on the drawings, the structures and/or machines will be built.

Materials

Raw materials used in metal fabrication include expanded, form and plate metal, fittings, castings, hardware and welding wire.

Cutting, Burning, and Forming

Cutting and burning are necessary to take the raw materials and make them the right shape. Some metal fabricators use cutting methods like band saws while others use burning methods like cutting torches and laser cutting tables. Many metal fabricators employ both cutting and burning methods. The next step in the metal fabrication process is forming the metal and this is accomplished with a hydraulic brake press. Tube-bending machines, wheeling machines and rolling machines are also used to shape metal.

Machining and Welding

The metal fabricator uses machining and welding to complete construction. Machining capability is usually limited in a metal fabricator, but magnetic drills, metal lathes and mills are common. On the other hand, welding is the most important job of a metal fabricator. Once the cutting, burning, forming and machining has been completed these parts will be welded together based on the engineering drawings.

The Final Product

Once the parts have been welded together and cooled they are then usually primed and then painted. Any other details will be finished and the product will be inspected to ensure it has been built properly. Then it's ready for customer pick up or shipping.

A typical steel fabrication shop

Methods and Techniques of NDT

NDT is divided into various methods of nondestructive testing, each based on a particular scientific principle. These methods may be further subdivided into various techniques. The various methods and techniques, due to their particular natures, may lend themselves especially well to certain applications and be of little or no value at all in other applications. Therefore choosing the right method and technique is an important part of the performance of NDT.

• Acoustic emission testing (AE or AT)
• Electromagnetic testing (ET)
• Ellipsometry
• Guided wave testing (GWT)
• Hardness testing
• Impulse excitation technique (IET)
• Infrared and thermal testing (IR)
• Laser testing
• Leak testing (LT) or Leak detection
• Magnetic resonance imaging (MRI) and NMR spectroscopy
• Optical microscopy
• Positive Material Identification (PMI)
• Radiographic testing (RT)
• Scanning electron microscopy
• Ultrasonic testing (UT)
• Visual inspection (VT)
• Pipeline video inspection

An example of a 3D replicating technique. The flexible high-resolution replicas allow surfaces to be examined and measured under laboratory conditions. A replica can be taken from all solid materials.

EXAMPLE of NDT

Weld verification

In manufacturing, welds are commonly used to join two or more metal surfaces. Because these connections may encounter loads and fatigue during product lifetime, there is a chance that they may fail if not created to proper specification. For example, the base metal must reach a certain temperature during the welding process, must cool at a specific rate, and must be welded with compatible materials or the joint may not be strong enough to hold the surfaces together, or cracks may form in the weld causing it to fail. The typical welding defects, lack of fusion of the weld to the base metal, cracks or porosity inside the weld, and variations in weld density, could cause a structure to break or a pipeline to rupture.

Welds may be tested using NDT techniques such as industrial radiography using X-rays or gamma rays, ultrasonic testing, liquid penetrant testing or via eddy current. In a proper weld, these tests would indicate a lack of cracks in the radiograph, show clear passage of sound through the weld and back, or indicate a clear surface without penetrant captured in cracks.

Welding techniques may also be actively monitored with acoustic emission techniques before production to design the best set of parameters to use to properly join two materials.

Structural mechanics

Structures can be complex systems that undergo different loads during their lifetime. Some complex structures, such as the turbomachinery in a liquid-fuel rocket, can also cost millions of dollars. Engineers will commonly model these structures as coupled second-order systems, approximating dynamic structure components with springs, masses, and dampers. These sets of differential equations can be used to derive a transfer function that models the behavior of the system.

In NDT, the structure undergoes a dynamic input, such as the tap of a hammer or a controlled impulse. Key properties, such as displacement or acceleration at different points of the structure, are measured as the corresponding output. This output is recorded and compared to the corresponding output given by the transfer function and the known input. Differences may indicate an inappropriate model (which may alert engineers to unpredicted instabilities or performance outside of tolerances), failed components, or an inadequate control system.

Radiography in medicine

As a system, the human body is difficult to model as a complete transfer function. Elements of the body, however, such as bones or molecules, have a known response to certain radiographic inputs, such as x-rays or magnetic resonance. Coupled with the controlled introduction of a known element, such as digested barium, radiography can be used to image parts or functions of the body by measuring and interpreting the response to the radiographic input. In this manner, many bone fractures and diseases may be detected and localized in preparation for treatment. X-rays may also be used to examine the interior of mechanical systems in manufacturing using NDT techniques, as well.

Chest radiography indicating a peripheres bronchialcarcinom.

1. Section of material with a surface-breaking crack that is not visible to the naked eye.
2. Penetrant is applied to the surface.
3. Excess penetrant is removed.
4. Developer is applied, rendering the crack visible.

Non Destructive Testing

Nondestructive testing (NDT) is a wide group of analysis techniques used in science and industry to evaluate the properties of a material, component or system without causing damage. Because NDT does not permanently alter the article being inspected, it is a highly-valuable technique that can save both money and time in product evaluation, troubleshooting, and research. Common NDT methods include ultrasonic, magnetic-particle, liquid penetrant, radiographic, and eddy-current testing. NDT is a commonly-used tool in forensic engineering, mechanical engineering, electrical engineering, civil engineering, systems engineering, aeronautical engineering, medicine, and art.