NASA Tech Briefs: What is the function/purpose of the Materials, Processes & Manufacturing Department (MP&MD)? Dr. Munafo: We develop new materials and bring them to maturity. We work with the research centers that work with materials in test tubes and in coupon forms – what we call low technology readiness levels – and we advance the technology readiness level by building real parts from the materials as well as by testing them. So, we’re in the materials technology maturation business for the agency. We also do research on manufacturing processes and we are primary in that arena. We do the low-level research as well as developing and maturing processes to where they can be used in flight systems. That’s the processes part. Finally, we build prototypes and test hardware that’s used to demonstrate the feasibility of the design. We do this mainly for projects at Marshall, although we have lately become involved with many other centers’ projects through our problem-solving initiatives. We are also very strong in failure analysis. NTB: Can you explain what the shuttle orbiter flow liners are and what happened to them last year? Dr. Munafo: The flow liners are mechanical devices that line the inside of the large lines that transfer hydrogen and oxygen from the external tanks to the space shuttle main engines. Those lines have to pass through the orbiter, so there is an interface leaving the external tank and another one in the orbiter, which the interface attaches too. The lines pass through the orbiter compartment to the back where they hook up with the engines (the engines are attached to the other ends of the lines), and when the oxygen and hydrogen rush through there, a lot of vibration and pressure force from flow is created. In order for those lines to bend, they incorporate several of what we call bellows joints, which look like accordion-shaped pipes that can bend freely in any direction like a flexible straw. The bellows are not very strong against the pressure and flow loads, so on the inside of them there is a nesting pair of cylindrical flow liners that are six to eight inches long and about 17” in diameter and these nest together. One end of each of the pairs is welded to the strong part of the bellows – the ends where it’s reinforced with heavy metal. The other end floats kind of freely and nests with the forward shield, then it nests with the aft shield, which in turn is welded to the aft end of the bellows structure. As the fluid comes through, it prevents it from impinging directly on the inside of the accordion-like bellows. They also have to be cleaned, because the systems are very sensitive to contamination and when the shuttle is being refurbished, the engines that go on those bellows are right there – visible – because the last bellows joint is right at the interface between the engines and the orbiter. In order to clean the nested pair, they have holes around the circumference for draining after they are washed out with fluid. It was at these holes that the cracks started. NTB: What was the “complex welding procedure” used to repair the flow liners? Dr. Munafo: Tungsten arc welding is a process that we brought to maturity 20 to 30 years ago. It was not the most common welding method when it was developed. But because it is so much cleaner than the kind of welding done in shipyards and bridge building, it was incorporated into welding space hardware. In tungsten arc welding, the electric arc is struck between a tungsten pointed rod and a workpiece. So, you have an electric current flowing from the rod to the workpiece making this very brilliant, hot arc in the process. This causes the piece being worked on to melt and then filler metal is fed in from the side to replace the metal that’s melting away and to build up or fill in the weld groove. We have several of those setups here in our lab. This technique is used in much of our welding here, but it was really necessary on the shuttle system’s engine, which contains literally thousands of complex welds, because the process is much more flexible than old-fashioned welding. We pretty routinely repair welds on the engines. We had used this process not only for making primary welds, but also for repairing welds that include defects or that get cracked or damaged somehow. NTB: Can you discuss the training simulator you and your team developed and the evaluation process used to test the repairs? Dr. Munafo: The unique thing about these particular weld repairs is that they were being done in situ – on hardware that had already been installed in the orbiter. We didn’t have access to clean rooms, and we couldn’t get X-rays in there very easily to judge the quality of the welds. We didn’t even have access to the backsides since the flow liners themselves are welded into the structure of the feed lines, and you can’t get at the back side for any meaningful inspection process. In order to make sure that it would work, that we would be able to clean out any debris that got in there, and that we just had access, we built a simulator that had two flow liners nested together in the associated welds that joined the back and forward ends of the forward and aft flow liners, respectively. We also built machine rings that were in the same configuration as the inside of the convoluted bellows. When the welder is on the inside of the 17” line, he can see the flow liners, and inside of those – just barely visible through those drain holes – you can see the convolutes of the bellows. We constructed the simulator from the welder’s point of view, so he could stick his head in the hole, get into position, and weld. We were also able to make contamination measurements. We would flush out the inside of the simulator and get it clean, and then go in and weld it. We would simulate all of the shielding that we were going to do, because you can’t simply go into the back of a liquid oxygen or liquid hydrogen system and just weld away. It has to be absolutely clean, because any bit of contamination will ignite and start a fire. We also used it to develop the masking techniques to keep debris from getting into the holes and developed a process to make sure that we didn’t get dirt inside. As a further check, we deliberately introduced contamination into the simulator and developed a process for cleaning that would remove it. So the simulator became very necessary for repairing the orbiter successfully. Normally,
when we certify a new process or a new material, we test it full scale
in the test stands to make sure that it is working
right – that
the stresses and strains, and the induced loads in it are what we calculated
them to be. None of that was in the cards for the flow liners, because
we don’t
have a ground test vehicle that we can certify new things like that on.
In order to certify the repairs, we had to develop customized
material testing
techniques for simulating those repairs and then test them under the
same loads they receive in service. That was quite an extensive
operation with a lot of
analysis. NTB: What commercial/practical applications does the MP&MD work on? Dr.
Munafo: We do
have a select group of scientists in this department who develop new
materials and more commonly, scientists who are looking
to expand the horizons of the new materials that have been developed
at the NASA research centers in order to use them in hardware. For instance,
one of our scientists extended the technology for an aluminum alloy that
we are using for pump housings and what we call static parts, which are
parts that don’t rotate, and he adapted it for the automotive industry. Now other
companies have learned we are here. For example, Evinrude outboard
motors advertise their latest line of motors as featuring
NASA-developed
technology to reduce their emissions and to make their engines more
efficient that is based on another material that was developed
in this department. NTB: What is your department currently working on? Dr. Munafo: We are always working to improve and upgrade materials and processes. One of our scientists is working on the Columbia accident. We are working to improve processes of applying foam to the external tank, which has to be done. We are also working on developing some new high-temperature ceramic materials, which are currently available only in very small sizes – wafer and pencil-sized pieces. We are working on making those big enough so we can use them in the new orbital space plane – the vehicle that will be used for rescues – because it will be critical to have high-temperature materials for re-entry. We are actually going to build the orbital space plane here in our department. We are also participating in the on-orbit repair development, which is the ability to repair things in orbit; in particular the tiles and the wing leading edges. We are repairing the boom that goes from the orbiter, because one of them broke recently. We’re developing a process for repairing anything in orbit using rapid prototyping. This is a technology that builds hardware by selectively melting and sintering a powder with a laser to get the part or shape that is needed. When the melting and sintering is finished, the box is opened and you’ve got yourself a new part. We now have a microwave-sized unit that will go on the space station. Anytime a part is broken, a powder disk, which has all the geometries of all the parts in a suitable format, is simply inserted into the machine. The part number is punched in and in no time out comes the necessary replacement part. We’re hoping to expand this technology to the tiles, since every one of those tiles has a different shape. Basically, any kind of process, be it land-based or space-based, is what we develop and work on in the Materials, Processes, and Manufacturing Department. Resources:
Previous interviews: October
2003 September
2003 August
2003
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