Transparent Overlay for Laser Peening

In the application of laser peening, two overlays are applied to the surface to be laser peened: opaque and transparent.  Both are employed to improve the effectiveness of laser peening.  The first overlay that is applied to the surface is an opaque overlay, typically aluminum or black vinyl tape, which absorbs energy from the laser pulse and generates a high-temperature plasma of 10,000o C.  The second overlay is transparent to the laser beam, typically flowing water, acting as a tamping mechanism to confine the expansion of the plasma.  An illustration of the process is shown below.  As the plasma blows through the water, a shock wave is created that enters the surface of the part, plastically deforming the surface and producing a compressive residual stress field that enhances the fatigue properties of the part.

laser peening transparent overlay

The surface of the part is protected from the high temperature plasma by the tape. During the life of the very short laser pulse, typically less than 30 billionth of a second, there is insufficient time for the plasma to burn through the tape and damage the part.  The water has no effect on cooling the high temperature of the plasma during this short period.  The water is used to intensify the shock wave by tamping the expansion.  By acting as a momentarily tamping mechanism, it increases the intensity of the shock wave and its lifetime – thus enabling the production of a deeper and more intense residual stress field.


F-35 Fleet Continues to Grow

Today, The U.S. Department of Defense announced additional purchases of the F-35 from Lockheed Martin Corp, with the award of a contract in excess of $5 billion.   The award is for the low-rate initial production of Lot IX of the F-35 Lightning II Joint Strike Fighter advance acquisition contract.  The contract provides for the procurement of 41 F-35A aircraft: 26 for the U.S. Air Force; six for Norway; seven for Israel; two for Japan; twelve F-35Bs: six for the U.S. Marine Corps, and six for the British Royal Navy; and two F-35Cs for the U.S. Navy.  Delivery is expected to be completed by December, 2017.  The planes are being manufactured and assembled in several states in the U.S.: Texas, California, Florida, New Hampshire, and Maryland; and in the United Kingdom and Japan.  The contract is being handled through the Naval Air Systems Command in Patuxent River, Maryland. 

For more information, read the News on the F-35 website, www.f35.com, or the DoD website.

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