Selection and Preservation of fracture surfaces The proper selection, preservation, and cleaning of fracture surfaces is vital to prevent important evidence from being destroyed or obscured. Surfaces of fractures may suffer either mechanical or chemical damage. Mechanical damage may arise from several sources, including the striking of the surface of the fracture by other objects. This can occur during actual fracture in service or when removing or transporting a fractured part for analysis Usually, the surface of a fracture can be protected during shipment by a cloth or cotton covering, but this may remove some loosely adhering material that might contain the primary clue to the cause of the fracture. Touching or rubbing the surface of a fracture with the fingers should definitely be avoided. Also, no attempt should be made to fit together the ections of a fractured part by placing them in contact. This generally accomplishes nothing and almost always causes damage to the fracture surface. The use of corrosion-inhibiting paper to package samples should be considered Chemical(corrosion) damage to a fracture specimen can be prevented in several ways. For instance, because the of the fracture, many laboratories prefer not to use corrosion-preventive coatings on a fracture specimen. When posite c identification of foreign material present on a fracture surface may be important in the overall determination of the cause it is best to dry the fracture specimen, preferably using a jet of dry, compressed air(which will also blow extraneous foreign material from the surface), and then to place it in a dessicator or pack it with a suitable dessicant. However, clean, fresh fracture surfaces should be coated when they cannot be protected from the elements. After failure of large structures several days may be required to remove critical specimens, and so coating the fracture surfaces would be the prudent Cleaning of fractured surfaces should be avoided in general, but must be done for SEM examination and often to reveal acroscopic fractographic features. Cleaning should proceed in stages using the least aggressive procedure first, then proceeding to more aggressive procedures if needed. Washing the fracture surface with water should especially avoided. However, specimens contaminated with seawater or with fire-extinguishing fluids require thorough washing, usually with water, followed by a rinse with acetone or alcohol before storage in a dessicator or coating with a dessicant Sometimes cleaning may also be required for removal of obliterating debris and dirt, or to prepare the fracture surface for SEM examination. Other acceptable cleaning procedures include use of a dry-air blast or of a soft-hair artist's brush treating with inorganic solvents, either by immersion or by jet; treating with mild acid or alkaline solutions(depending the metal)that will attack deposits but to which the base metal is essentially inert; ultrasonic cleaning; and application and stripping of plastic replicas Cleaning with cellulose acetate tape is one of the most widely used methods, particularly when the surface of a fracture has been affected by corrosion. A strip of acetate about 0. 1 mm(0.005 in thick and of suitable size is softened by immersion in acetone and placed on the fracture surface. The initial strip is backed by a piece of unsoftened acetate, and then the replica is pressed hard onto the surface of the fracture using a finger. The drying time will depend on the extent to which the replicating material was softened, and this in turn will be governed by the texture of the surface of the fracture. Drying times of not less than 15 to 30 min are recommended. The dry replica is lifted from the fracture, using a scalpel or tweezers. The replicating procedure must be repeated several times if the fracture is badly contaminated. When a clean and uncontaminated replica is obtained, the process is complete. An advantage of this method is that the debris removed from the fracture is preserved for any subsequent examination that may be necessary for identification by x-ray or electron diffraction techniques. To be complete, the analyst should filter solvents used for cleaning to recapture insoluble particulates Sectioning. Because examination tools, including hardness testers and optical and electron microscopes, are limited as to the size of specimen they can accept, it is often necessary to remove from a failed component a fracture-containing portion or section that is of a size convenient to handle and examine. This is a destructive process and may spoil evidence n potential litigation cases Before cutting or sectioning, the fracture area should be carefully protected. All cutting should be done so that surfaces of fractures and areas adjacent to them are not damaged or altered; this includes keeping the fracture surface dry, whenever possible. For large parts, the common method of removing specimens is by flame cutting. Cutting must be done at a sufficient distance from the fracture site so that the microstructure of the metal underlying the surface of the fracture is not altered by the heat of the flame, and so that none of the molten metal from flame cutting is deposited on the surface of the fracture Heat from any source can affect metal properties and microstructures during cutting. Therefore, dry abrasive cutoff wheels should never be used near critical surfaces that will be examined microscopically. Therefore, sectioning should be performed with jewelers'saws, precision diamond-edged, thin cutoff wheels, hacksaws, band saws, or soft abrasive cutoff wheels flooded with water-based soluble oil solution to keep metal surfaces cool and corrosion-free. Dry cutting with an air-driven abrasive disk may also be used with care to remove small specimens from large parts if kept cool, along with coating the fracture surface for protection fracture surfaces for examination and study These cracks may provide more information than the primary facile se. Secondary Cracks. When the primary fracture has been damaged or corroded to such a degree that most of the information relevant to the cause of the failure is obliterated, it is desirable to open any secondary cracks to expose theirSelection and Preservation of Fracture Surfaces The proper selection, preservation, and cleaning of fracture surfaces is vital to prevent important evidence from being destroyed or obscured. Surfaces of fractures may suffer either mechanical or chemical damage. Mechanical damage may arise from several sources, including the striking of the surface of the fracture by other objects. This can occur during actual fracture in service or when removing or transporting a fractured part for analysis. Usually, the surface of a fracture can be protected during shipment by a cloth or cotton covering, but this may remove some loosely adhering material that might contain the primary clue to the cause of the fracture. Touching or rubbing the surface of a fracture with the fingers should definitely be avoided. Also, no attempt should be made to fit together the sections of a fractured part by placing them in contact. This generally accomplishes nothing and almost always causes damage to the fracture surface. The use of corrosion-inhibiting paper to package samples should be considered. Chemical (corrosion) damage to a fracture specimen can be prevented in several ways. For instance, because the identification of foreign material present on a fracture surface may be important in the overall determination of the cause of the fracture, many laboratories prefer not to use corrosion-preventive coatings on a fracture specimen. When possible, it is best to dry the fracture specimen, preferably using a jet of dry, compressed air (which will also blow extraneous foreign material from the surface), and then to place it in a dessicator or pack it with a suitable dessicant. However, clean, fresh fracture surfaces should be coated when they cannot be protected from the elements. After failure of large structures several days may be required to remove critical specimens, and so coating the fracture surfaces would be the prudent decision. Cleaning of fractured surfaces should be avoided in general, but must be done for SEM examination and often to reveal macroscopic fractographic features. Cleaning should proceed in stages using the least aggressive procedure first, then proceeding to more aggressive procedures if needed. Washing the fracture surface with water should especially be avoided. However, specimens contaminated with seawater or with fire-extinguishing fluids require thorough washing, usually with water, followed by a rinse with acetone or alcohol before storage in a dessicator or coating with a dessicant. Sometimes cleaning may also be required for removal of obliterating debris and dirt, or to prepare the fracture surface for SEM examination. Other acceptable cleaning procedures include use of a dry-air blast or of a soft-hair artist's brush; treating with inorganic solvents, either by immersion or by jet; treating with mild acid or alkaline solutions (depending on the metal) that will attack deposits but to which the base metal is essentially inert; ultrasonic cleaning; and application and stripping of plastic replicas. Cleaning with cellulose acetate tape is one of the most widely used methods, particularly when the surface of a fracture has been affected by corrosion. A strip of acetate about 0.1 mm (0.005 in.) thick and of suitable size is softened by immersion in acetone and placed on the fracture surface. The initial strip is backed by a piece of unsoftened acetate, and then the replica is pressed hard onto the surface of the fracture using a finger. The drying time will depend on the extent to which the replicating material was softened, and this in turn will be governed by the texture of the surface of the fracture. Drying times of not less than 15 to 30 min are recommended. The dry replica is lifted from the fracture, using a scalpel or tweezers. The replicating procedure must be repeated several times if the fracture is badly contaminated. When a clean and uncontaminated replica is obtained, the process is complete. An advantage of this method is that the debris removed from the fracture is preserved for any subsequent examination that may be necessary for identification by x-ray or electron diffraction techniques. To be complete, the analyst should filter solvents used for cleaning to recapture insoluble particulates. Sectioning. Because examination tools, including hardness testers and optical and electron microscopes, are limited as to the size of specimen they can accept, it is often necessary to remove from a failed component a fracture-containing portion or section that is of a size convenient to handle and examine. This is a destructive process and may spoil evidence in potential litigation cases. Before cutting or sectioning, the fracture area should be carefully protected. All cutting should be done so that surfaces of fractures and areas adjacent to them are not damaged or altered; this includes keeping the fracture surface dry, whenever possible. For large parts, the common method of removing specimens is by flame cutting. Cutting must be done at a sufficient distance from the fracture site so that the microstructure of the metal underlying the surface of the fracture is not altered by the heat of the flame, and so that none of the molten metal from flame cutting is deposited on the surface of the fracture. Heat from any source can affect metal properties and microstructures during cutting. Therefore, dry abrasive cutoff wheels should never be used near critical surfaces that will be examined microscopically. Therefore, sectioning should be performed with jewelers' saws, precision diamond-edged, thin cutoff wheels, hacksaws, band saws, or soft abrasive cutoff wheels flooded with water-based soluble oil solution to keep metal surfaces cool and corrosion-free. Dry cutting with an air-driven abrasive disk may also be used with care to remove small specimens from large parts if kept cool, along with coating the fracture surface for protection. Secondary Cracks. When the primary fracture has been damaged or corroded to such a degree that most of the information relevant to the cause of the failure is obliterated, it is desirable to open any secondary cracks to expose their fracture surfaces for examination and study. These cracks may provide more information than the primary fracture