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Abstract:Over the years, several bare metal and crack-based strain sensors have been proposed for various fields of science and technology. However, due to their low gauge factor, metal-based strain sensors have limited practical applications. The crack-based strain sensor, on the other hand, demonstrated excellent sensitivity and a high gauge factor. However, the crack-based strain sensor exhibited non-linear behavior at low strains, severely limiting its real-time applications. Generally, the crack-based strain sensors are fabricated by generating cracks by bending a polymer film on which a metal layer has been deposited with a constant curvature. However, the random formation of cracks produces nonlinear behavior in the crack sensors. To overcome the limitations of the current state of the art, we propose a V-groove-based metal strain sensor for human motion monitoring and Morse code generation. The V-groove crack-based strain sensor is fabricated on polyurethane acrylate (PUA) using the modified photolithography technique. During the procedure, a V-groove pattern formed on the surface of the sensor, and a uniform crack formed over the entire surface by concentrating stress along the groove. To improve the sensitivity and selectivity of the sensor, we generated the cracks in a controlled direction. The proposed strain sensor exhibited high sensitivity and excellent fidelity compared to the other reported metal strain sensors. The gauge factor of the proposed V-groove-induced crack sensor is 10-fold higher than the gauge factor of the reported metal strain sensors. In addition, the fabricated V-groove-based strain sensor exhibited rapid response and recovery times. The practical feasibility of the proposed V-groove-induced crack-based strain sensor is demonstrated through human motion monitoring and the generation of Morse code. The proposed V-groove crack sensor can detect multiple motions in a variety of human activities and is anticipated to be utilized in several applications due to its high durability and reproducibility.Keywords: polyurethane-acrylate (PUA); crack-based strain sensor; high sensitivity; excellent fidelity; human motion monitoring

The purpose of using a notched sample is to create a fatigue crack by applying cyclic loading through pins inserted into the holes on the sample using a laboratory fatigue test machine. The fatigue crack will begin on the point of the notch and extend through the sample. The length of the crack is typically monitored by measuring the compliance of the coupon which changes as the crack grows, or direct measurement using an optical microscope to measure the position of the crack tip or indirectly from either extensometer readings of the crack mouth opening or attaching strain gauges to the backface of the coupon.[3]

Detection of wafer/die crack after the wafer dicing process is important for yield rate control prior to packaging. The traditional approach of microscopic examination is done after the dies are stripped from the dicing tape, and further crack propagation could result from this pick-and-place process. An on-tape crack inspection technique is proposed in this paper so that the crack from the dicing process can be clearly identified. The issues of seeing through the silicon substrate and the scattering at the dicing tape have been resolved, respectively, using a near-infrared wavelength of 1100 nm for illumination and using a feeding index matching liquid for filling the rough surface of the tape. Both the illumination and imaging optics of the inspection system have been designed and simulated with a ray-tracing program, and the prototype demonstrates the ability of seeing through the silicon substrate and dicing tape as well as detecting micro-crack down to 1.25 μm, whose resolution is sufficient for most applications of die crack inspection.

This chapter considers the fracture behaviour of propagating and subsequently arresting cracks and of cracks under impact loading. Loading techniques and measuring methodologies for determining the crack arrest toughness KIc and the impact fracture toughness KId are discussed. Conventional measuring procedures are outlined; the validity and the applicability range of these procedures are critically examined. Furthermore, the physical processes that control the various dynamic events are analyzed by means of a special optical technique which determines the dynamic stress intensity factor directly from the local stress strain field at the crack tip. On the basis of the established results, improved measuring techniques are developed that are capable of determining true dynamic material strength properties at arbitrary test conditions without any restrictions in crack propagation velocity, loading rate, load duration, etc. 2b1af7f3a8