Sandia LabNews

Shock therapy: With renovations, Sandia’s workhorse Mechanical Shock Facility ready to take on more jobs


TEST PREPARATION — Neil Davie (left) and Adam Slavin (both 1534) demonstrate putting a component into a test fixture in front of the Mechanical Shock Facility’s new 20-inch actuator, which was part of a yearlong renovation project on the facility. (Photo by Randy Montoya)

Sandia’s newly renovated Mechanical Shock Facility in Tech Area 3 looks much as it always did from the outside, a tall metal building bumped up against a concrete bunker. But after a year of construction, the facility reopened with two actuators that can take on tests it couldn’t do before.

The actuators feature new design principles, largely internal, developed by Mechanical Shock test director Neil Davie (1534). This design produces higher speed shock tests with improved quality for Sandia’s shock-testing mission, most of which concern weapons components or subsystems, Neil says.

Senior manager Dennis Miller (1530) says the facility fills a critical gap between tests that can be conducted in small laboratory-scale facilities and those that require the high speeds and energy levels of the Rocket Sled Test Facility.

“The Mechanical Shock Facility can accommodate sizeable test packages and achieve impressive test velocities,” Dennis says.

Mechanical Shock went back into operation in mid-September, and Neil and Adam Slavin (1534) say its test schedule is filling up. The facility is part of the Validation and Qualification Sciences Experimental Complex, where components are subjected to abnormal environments to make sure they will perform safely and reliably under all kinds of conditions.

The actuators are similar to a large hydraulic cylinder with a piston and piston rod. Mechanical Shock’s two actuators are operated pneumatically, however.

Here’s how it works: You pressurize the chamber behind the piston with nitrogen gas held in equilibrium by means of a special seal. You park a 750-pound ram sled — a large block of gold-colored aluminum — up against the actuator on a sled track and park the target sled about 15 feet down the same track. A valve is opened, breaking the seal and sending high pressure rushing into a chamber. That propels the piston out at hundreds of miles an hour, shooting the ram sled into the target sled, which has the test item bolted to the side opposite the collision.

The shot occurs in mere milliseconds. You’d miss it if you blinked while watching the closed-circuit television housed in a horseshoe-shaped bank of controls in an adjoining room.

A different operating principle

Mechanical Shock’s new 20-inch actuator — the measurement refers to the internal piston size — uses a fundamentally different operating principle than the aging 18-inch actuator it replaced, Neil says.

 “Because of the design changes, we are able to get significantly higher speeds,” which he says was a key reason behind renovating the nearly 50-year-old facility that was last refurbished in the 1980s. 

“The higher speeds provide an expanded mission space to do tests we couldn’t do on an actuator before.  Overall, the shock pulses that we can produce are more repeatable and higher quality,” Neil says.

The new actuator can accelerate sleds at up to 350 feet per second, although in the first weeks after reopening it ran tests at about 200 feet per second along the 120-foot track that replaced the previous

90-foot track.

Speed, the weight on the sleds, and the felt, rubber, or plastic cushioning mounted between the sleds determine the shock pulse exerted on the test item, Neil says. Impacts simulate shock ranging from tens of G’s to several thousand G’s. A recent test used 10 inches of felt, taped into a stack, to produce a 4,000 G shock.

“We go through lots of yellow tape (securing felt pads to sleds),” jokes Adam, who will take over when Neil retires Dec. 23.

A 12-inch actuator built in 2005 served as a prototype for evaluating the new design. The prototype replaced an older 12-inch actuator and is used for testing smaller components.

“The new actuators are more reliable and the new sleds are more reliable, so we spend more time on working on the true mission of shock testing and not so much on the care and feeding of the hardware,” says Adam.

The renovation eliminated a twin-rail track, which Neil says was difficult to align and prevented sleds from gliding smoothly. Now the sleds travel on a precision-machined and aligned monorail, a sophisticated version of a design used at Sandia decades ago, he says.

The actuators are operated at pressures up to 5,000 psi using nitrogen gas converted from liquid nitrogen stored on-site. Neil says the nitrogen supply system has the advantage of being clean and more rapidly replenished, lessening the turn-around time between tests compared to the high-pressure air compressor it replaced.

It was “a risky leap of technology” to turn to the new actuator design because the machine alone cost more than $1 million and the pneumatic seals are being used well beyond speeds approved by the seal manufacturer, Neil says.

The rest of the work included such things as the nitrogen system, fire suppression, safety systems, and general renovation, says Paul Schlavin (4822), Test Capability Revitalization (TCR) project manager. TCR is aimed at revitalizing large-scale test capabilities to allow the Labs to continue to lead in stockpile stewardship, weapon design and modeling, and simulation science.

Rod May (1505), program manager on the Mechanical Shock renovation, says TCR work will bring many of Sandia’s large-scale test facilities up to current standards and allow them to operate for the next 10 to 15 years.

Upcoming TCR projects include more work on Mechanical Shock, plus work on the 10,000-foot Rocket Sled Track, Large Centrifuge, and Vibration facilities, all in  Tech Area 3, and the wind tunnel in Tech Area 1’s Experimental Aerosciences facility, Paul says. He breaks it down this way: Phase 1 (2001-2005) completed projects on the Aerial Cable and Thermal Test Complex, while Phase 2 (2005-2013) has plans to upgrade facilities and equipment in both Tech Area 1 and Tech Area 3.

Some years, Mechanical Shock might do 10 to 15 projects, each needing five to 10 tests, Neil says. Each program also might require calibration shots to adjust test parameters to its particular needs.

Neil and Adam estimate the renovated facility can do up to five shots a day. They predict a busy future with upcoming programs.

That makes Neil’s upcoming retirement after 33 years at Sandia bittersweet.

“My previous manager said, ‘Neil, you can’t retire. You have all these new toys to bring up to speed and use to develop new techniques with,’” he says.