Page 66


www.us-tech.com


June, 2018


Building Fiber Optic Strain Sensors into Metal Components


By Adam Hehr, Research Engineer, Fabrisonic, LLC C


onventionally attached to the outside of a component or device, sensors detect and


respond to external stimuli, control- ling the equipment on which they are mounted. Now, it is possible to build sensors into the metal matrix of a piece of equipment with 3D metal printing.


External mounting can confuse


data collection, reduce the informa- tion gained and create challenges for sensor attachment, due to the use limits of adhesives, such as high tem- peratures or humid environments. It is beneficial to build these sensors into the metal matrix directly to pro- vide in situ information and to pro- tect them.


Ultrasonic Additive Manufacturing


Ultrasonic additive manufac-


turing (UAM) is a 3D metal printing technology that uses high-frequency


Ultrasonic additive


manufacturing (UAM) uses high-frequency ultrasonic vibrations to scrub metal foils together layer by layer.


ultrasonic vibrations to scrub metal foils together layer by layer. Other


methods use a directed heat energy source, such as a laser or e-beam. UAM systems are integrated into computer numerical control (CNC)


Melt-based 3D metal printing has been used to build some fiber types into metal, yet voids around the fiber, atmosphere requirements,


temperature measurements. An example of this technology


can be seen in Figure 1, where an instrumented bracket is shown along with a micrograph of a consolidated fiber. The fiber is fully integrated into the metal matrix. Fundamental work has shown


that the joint strength between the fiber and metal matrix is stronger than the yield stress of the metal and that the joint does not degrade with fatigue loading. Fabrisonic collaborated with


Figure 1: Bracket shown with sensors embedded near the


stress riser (left) and micrograph showing complete encapsulation of the fiber in aluminum.


frameworks to enable subtractive manufacturing alongside the ultra- sonic additive process. Ultra sonic joining is a solid-state process (no melting), enabling direct integration of temperature-sensitive components into the 3D metal part. Fiber optic strain sensors are


particularly vulnerable, due to their temperature-sensitive inscriptions, common commercially available plas- tic coatings and large thermal expan- sion mismatch with many metal alloys (susceptibility to cracking).


dimensional accuracy, and cracking remain challenges. To embed small fiber materials


into a metal part, a channel path is cut during the CNC stage of the UAM process. The fiber is placed into the channel and consolidated with the additive stage. Metal flow in the UAM process — similar to metal flow in friction stir welding — creates a strong mechanical joint between the matrix and sensor material. This in turn enables excellent strain transfer to the metal matrix for stress and


EWI’s mechanical test lab to perform testing. The joint robustness allows the technology to be scaled up and its applications evaluated. EWI is an engineering and technology organiza- tion that works to develop, test and implement industrial manufacturing technologies in North America. The team is also working with


NASA Langley Research Center for ad vanced mechanical testing and analysis.


Technology Outlook Building fiber optic strain sen-


sors into metal using UAM is still in its infancy, yet the technology is very promising. To help with technology transition and adoption, the team is working to explore other key areas.


Continued on page 70


Page 1  |  Page 2  |  Page 3  |  Page 4  |  Page 5  |  Page 6  |  Page 7  |  Page 8  |  Page 9  |  Page 10  |  Page 11  |  Page 12  |  Page 13  |  Page 14  |  Page 15  |  Page 16  |  Page 17  |  Page 18  |  Page 19  |  Page 20  |  Page 21  |  Page 22  |  Page 23  |  Page 24  |  Page 25  |  Page 26  |  Page 27  |  Page 28  |  Page 29  |  Page 30  |  Page 31  |  Page 32  |  Page 33  |  Page 34  |  Page 35  |  Page 36  |  Page 37  |  Page 38  |  Page 39  |  Page 40  |  Page 41  |  Page 42  |  Page 43  |  Page 44  |  Page 45  |  Page 46  |  Page 47  |  Page 48  |  Page 49  |  Page 50  |  Page 51  |  Page 52  |  Page 53  |  Page 54  |  Page 55  |  Page 56  |  Page 57  |  Page 58  |  Page 59  |  Page 60  |  Page 61  |  Page 62  |  Page 63  |  Page 64  |  Page 65  |  Page 66  |  Page 67  |  Page 68  |  Page 69  |  Page 70  |  Page 71  |  Page 72  |  Page 73  |  Page 74  |  Page 75  |  Page 76  |  Page 77  |  Page 78  |  Page 79  |  Page 80  |  Page 81  |  Page 82  |  Page 83  |  Page 84  |  Page 85  |  Page 86  |  Page 87  |  Page 88  |  Page 89  |  Page 90  |  Page 91  |  Page 92  |  Page 93  |  Page 94  |  Page 95  |  Page 96  |  Page 97  |  Page 98  |  Page 99  |  Page 100  |  Page 101  |  Page 102  |  Page 103  |  Page 104