Crack LINK Agilent ADS 2009 Update 1

by gerreyb
Published: November 23, 2022 (2 weeks ago)

Crack LINK Agilent ADS 2009 Update 1


CRACK Agilent ADS 2009 Update 1

the fracture toughness is typically measured by standard crack-bridging technique 34, 35 , with a side-crack length 2b that is typically more than a half of the sample width. we believe that this large crack extension is one of the reasons for the low fracture toughness of graphene. therefore, we employ a micromechanical device (fig. 4a ) that is integrated with a nanoindenter (fig. 4b ) to allow a nanoscale crack to bridge a pre-crack of length <2 a0. the micromechanical device is fabricated using a polydimethylsiloxane (pdms) elastomer, which is transparent to soft x-ray. the sample is placed on a pdms-coated glass slide, and then the micromechanical device is bonded to the pdms surface using the silicone-based adhesive. a pre-crack with length <2 a0 is introduced by fib. the deformation is recorded continuously in the form of z displacement of a microsphere via the afm cantilever mounted on the nanoindenter, with feedback control of the nanoindenter, as shown in fig. 4c. when the pre-crack reaches the microsphere, the corresponding deformation is recorded as the z displacement of the microsphere. figure 4d shows the displacement-time and displacement-displacement curves, which are extracted from the recorded deformation signals using an in-house matlab program. with the displacement-time curve ( fig. 4e ), the crack length can be extracted at each moment, providing a fracture toughness of ~3.5mpa.m

the nanoscale crack in graphene is created using a fib system, which is based on a ga+ ion beam with a 30kv acceleration voltage and a 30na beam current. as the pre-crack extends along the arm of the nanoindenter, the beam current is continuously reduced to avoid thermal damage to graphene. the size and position of the nanoscale crack are determined in real time using a combination of afm and optical microscopy. figure 5a shows the optical micrograph of the pre-crack in graphene that is formed by a continuous fib process. a crack is first formed with a typical size of ~100nm. the crack growth is monitored in situ by a high-resolution sem (nova nanosem430, fei), as shown in fig. 5b. the displacement-time and displacement-displacement curves are recorded and the crack length is extracted with an in-house matlab program. figure 5c shows the displacement-time and displacement-displacement curves, which are extracted from the recorded deformation signals. with the displacement-time curve ( fig. 5d ), the crack length can be extracted at each moment. the crack length increases with the pre-crack length, and the crack growth rate reaches ~10-3nm/s at the critical stress for mechanical failure. from the displacement-displacement curve ( fig. 5e ), the final crack length is also extracted, from which the corresponding critical stress for failure is derived. the average value of the critical stress for failure is 30mpa.

there are two ways to combat the problem. the first method is to design the circuit in such a way that the rise and fall times of the circuit are short enough so that the distortion is not significant. the second method is to use a circuit that has minimal coupling capacitance. the small coupling capacitance of a high impedance oscilloscope provides a flat response. therefore, the distortion caused by the circuit being tested will not be significant. the oscilloscope can then be used as a high impedance probe, which can be used to measure signals from the circuit being tested. in the agilent ads 2009 update, agilent has improved the harmonic balance simulator in ads, which is used to measure the distortion caused by the circuit being tested. the user can also optimize the circuit to reduce coupling capacitance.
the elastomeric actuator containing a suspended graphene coated with polydimethylsiloxane (pdms) was developed to apply non-uniform stress on the crack tip, and thus realize dynamic crack propagation ( fig. 3e ). the actuator is bonded to a thin film of pdms (1.1 mm thick) on a glass substrate. the actuator contains a beam with a circular indented area of radius a and width w (~500nm). upon the crack reaching the circular-shaped indented area, the beam is buckled under the non-uniform stress. repeated action of the beam buckling deforms the pdms layer and results in the continuous dynamic propagation of the crack, leading to growth of the crack length l and thus a total strain of ld. the corresponding stress distribution on the cracked graphene can be calculated by the finite element analysis, which is shown in fig. 3f. under the same loading condition, the crack length l increases gradually with the crack opening displacement d from about 10nm to 2.5um. the crack length can also be controlled by adjusting the crack opening displacement d and the crack width w.

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