1. Field of the Invention
The present invention relates to a method of determining and utilizing the improved properties of solid materials that are subjected to shock waves, or laser peened, and more particularly, to a method of designing a work piece whereby an ascertainable design credit is calculated and utilized for materials subjected to laser shock peening, the design credit being due to the enhanced mechanical properties such as hardness, high cycle fatigue life, and fatigue strength.
2. Description of the Related Art
Treating surfaces with impacts, or xe2x80x9cpeeningxe2x80x9d solid materials is well known in the art and is an accepted process for improving the fatigue, hardness, and corrosion resistance properties of materials. Several methods of such surface treatment exist including the use of vibropeening, burnishing, shot peening, and laser shock processing (or laser shock peeningxe2x80x94hereinafter simply referred to as xe2x80x9claser shock processingxe2x80x9d).
The use of vibropeening, burnishing, and shot peening have long been utilized, but have significant disadvantages. Vibropeening and burnishing are limited to treating simple part geometries. The treatment of notches, complex curved surfaces, and cavities is generally not possible because of the difficulty of applying the tooling to the surface for reproducible, effective treatment.
In shot peening, many small shot or beads are directed at a high speed against a surface of the material. This peening process provides unpredictable results due to the inconsistent nature of firing the shot, and the shot or beads sometimes escape from the treatment equipment and scatter into the surrounding area. Since the shot or beads might get into surrounding machinery and cause damage, shot peening usually can not be used in a manufacturing line. Additionally, such shot peening can ordinarily not be used on machined surfaces without a high likelihood of creating surface roughness outside of specifications. Furthermore, shot peening is inconsistent in achieving uniform characteristics in the resulting solid material.
Laser shock processing has several advantages over the prior art. Laser shock processing can occur on a manufacturing line without danger to surrounding equipment, is easily focused on preselected surface areas, and further, provides deeper compressive residual stresses than other surface treatment processes. Furthermore, laser shock processing can be conducted in high temperature and high vacuum environments. Non-planar surfaces and complex geometries are easily treated with laser shock processing. Most importantly, laser shock processing yields consistent, predictable mechanical properties in the resulting solid material. Resulting hardness, strength, high cycle fatigue properties, and fatigue strength in a work piece can be reproducibly attained with laser shock processing.
Laser shock processing encompasses all of the advantages of the prior art methods of peening solid materials, and provides several additional advantages, including being repeatedly attainable, and consistently measurable. Formerly, engineers and manufacturers could not rely on the enhanced properties of shot peening in their design specifications. The varying results prohibited engineers and manufacturers from fully utilizing a consistent enhancement of physical properties in the solid material.
The present invention sets forth a method of designing a work piece made of a solid material, given the precise reliability of laser shock processing results. The method includes the steps of determining a set of desired fatigue properties and tolerances for the work piece, determining a first base material and a first set of properties that would satisfy the set of desired fatigue properties, determining a second base material and a second set of properties that fall short of the set of desired fatigue properties, determining a design credit for the second base material based on enhanced fatigue properties due to a laser shock peening process, and using the laser shock peened second base material in a work piece, wherein the second base material has an enhanced set of properties that satisfy the set of desired fatigue properties by incorporating the design credit.
The present invention, in another form thereof, comprises a method of designing an article of manufacture having material properties comprising the steps of determining a set of desired fatigue properties for the article utilizing a known design credit based on enhanced fatigue properties due to laser shock processing, and determining a base material and set of properties that meet that set of desired fatigue properties for the article, with adjustments being made for design credit.
The invention, in yet another form thereof, pertains to a method of designing an article of manufacture having material properties, the method comprising the steps of determining a set of desired properties for the article based on preliminary design criteria, utilizing a known design credit based on enhanced properties of candidate materials for the article due to laser shock processing, determining an allowable increase in the design requirements for the article incorporating the design credit for the candidate materials, selecting the candidate material giving the highest allowable increase in the design requirements incorporating the design credit, and using the selected candidate material in the work piece.
In one embodiment of the invention, the design credit comprises the difference between the non-laser shock processed material properties and the desired design fatigue properties, wherein the laser-shock treated fatigue properties are higher than the design properties. The invention, in another embodiment thereof, defines the design credit as the difference between the non-laser shock treated material properties and the laser shock processed material properties, wherein the property increase is not quite as high as the desired design properties, but is still acceptable for the application.
It is an advantage of this invention that once the enhanced fatigue and mechanical properties of a laser-shock treated solid material are determined, corresponding results can be expected from all future laser shock processing of the solid material. Because of the highly controllable and reproducible effects of laser shock processing, the expected mechanical properties of a given solid material can be calculated both before and after the laser peening process.
It is a further advantage of the present invention that an ascertainable quantity of the solid material is saved in the making of each work piece due to the fact that the desired mechanical properties such as hardness, high cycle fatigue life, fatigue strength, and corrosion fatigue resistance can be achieved using less material. Alternately, a different (and optimally less expensive) material may be identified by this method, the alternate material possessing the desired mechanical properties after being laser shock processed.