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Loose Oval Defects and Prevention
The Loose Oval Defects (LODs) is an inherent form of metallic fracture that occurs due to the dynamic growth and subsequent fracture of the oval-shaped cavities in the surface of high-strength components. This phenomenon is often associated with the manufacture of thin-walled high-strength components, such as those used in aerospace, automotive and automotive-related industries. LODs affects the strength, integrity, and reliability of components, resulting in safety and operational performance concerns.
This paper provides an overview of the causes, detection and prevention of Loose Oval Defects. Causes of LODs can include inadequate component surface preparation and electroless plating, lack of material countermeasures, and design flaws. LODs can be detected through visual inspection, eddy current measurements, and top-down ultrasonic testing. Preventive measures include the use of improved surface preparation techniques, materials selection, design changes, and proper deposition techniques.
LODs are often found on high-strength components that are produced for both safety-critical and operational purposes. The most common components affected include fracture-critical components used in aerospace and automotive applications, and components used in the manufacture of automobiles and related products. Compressing Loose Oval Defects (LODs) is a major concern for these industries, as it can cause stresses to essentially degrade the integrity of a component.
The fundamental mechanism behind Loose Oval Defects involves the internal fracturing of a pre-existing surface feature, typically a circular-shaped cavity, which causes fracturing along the entire circumference of the feature. The phenomenon is a result of the dynamic interfacial tension between the cavity and the surrounding material, which causes localized torsional stress in the high-strength material at the cavity interface. This stress results in the expansion of the cavity, and ultimately, the fracture of the surrounding material.
The causes of Loose Oval Defects include inadequate surface preparation and electroless plating, lack of material countermeasures, and design flaws. Poor surface preparation, or inadequate cleaning and degreasing, can leave microscopic cavities on the surface of the component. During electroless plating, microscopic air bubbles, which become trapped in the plating solution, can enter and become trapped on the surface of the component. As these bubbles expand, they force the surface of the component to fracture, leading to the formation of Loose Oval Defects. Design flaws, such as inadequate structural support, can also create an unfavorable environment for the development of Loose Oval Defects.
Various techniques can be used to detect Loose Oval Defects, including visual inspection, eddy current measurements, and top-down ultrasonic testing. Visual inspection requires that the components be viewed from top to bottom, looking for cavities, pits, and other signs of Loose Oval Defects. Eddy current measurements measure the electrical conductivity of the material and are used to identify surface and subsurface cavities and fractures. Top-down ultrasonic probes should be used to inspect components in order to detect Loose Oval Defects.
Preventive measures that can be taken in order to avoid the occurrence of Loose Oval Defects include improved surface preparation techniques, materials selection, design changes, and proper deposition procedures. In order to improve the surface preparation of components, degreasing and passivation should be completed before production begins. Proper materials selection is also important in order to minimize the risk of Loose Oval Defects, as certain materials are more prone to fracturing than others. Design changes may need to be implemented in order to reduce stress on parts and components, while deposition techniques should be optimized to ensure uniform and satisfactory coverage.
In conclusion, Loose Oval Defects are a form of metallic fracture that is often associated with high-strength components and can significantly degrade the integrity of the part or assembly. The causes of Loose Oval Defects include inadequate surface preparation, electroless plating, lack of materials countermeasures, and design flaws. Various techniques can be used to detect Loose Oval Defects, including visual inspection, eddy current measurements, and top-down ultrasonic testing. In order to prevent Loose Oval Defects from occurring, improved surface preparation procedures should be used, materials should be selected carefully, design changes should be made where necessary, and proper deposition procedures should be followed.
