Hosein Weekly Update

Eventually, we find the mechanical properties of our single crystal quartz. We contact the company and they sent us the paper includes all the properties. On their website they just upload Cij and Sij not others. So here is the properties:

tensile strength: 80 perpendicular-110 parallel (MPa); Bending: 90 perpendicular-135 parallel (MPa) .

Once I used the average value of 85 MPa as for \sigma_c, I saw very soon fracture in the sample and the simulation failed. But later when I increased the magnitude of till \sigma_c=300-350 Mpa, the fracture initiated at the time close to the peak of the applied force and capture the full crack propagation through the depth of the specimen.

So at this moment I conclude that either the code has some issues in calculating the correct stress matrix or the experimental data is overestimated.

Sun Group Weekly Update Aug. 9, 2016

This week I focused on plate lapping. There are three different types of plate for the experiment. The flyer plate and back target are easily lapped with high quality (below than 1 ring). The front target plate need longer time to lap, usually about 4 hours, which can result in 2 or 3 rings of flatness. The general profiles of lapped plate are acceptable. I am polishing the back target plate now and will work on real 600line/mm grating this week on back target plate and target assembly. I decide to put the grating first and then setup the target sandwich because the rotation of photolithography may generate specific patterns on granular specimen.

Protected: Hosein weekly Update

This content is password protected. To view it please enter your password below:

Protected: Alex Sun weekly update July 27 2016

This content is password protected. To view it please enter your password below:

Robinson Weekly Update

1.) Behind on schedule for data analysis (and writing) by 2 weeks

  • Finally got the code again working late last week so analysis of the next 5 tests should go fast
  • crack velocities peak at 1200 m/s, and mostly reside in the 100’s of m/s
  • force sensor seems to have an inherent response time of ~5 µs
  • force curves seem to have a second plateau after load drop
    • need to check if this is an artifact from the force sensor or genuinely linked to some fracture phenomena where the crack arrests temporarily

2.) Need to think harder about converting reaction force readout to stress intensity factor at the notch tip and comparing time till K=K_1c to time of failure. How far do I go down the road of quartz specific analysis as opposed to design of apparatus focus?

3.) Rough draft of introduction is nearing submission for first edit. All other sections are largely contingent on data analysis although introduction is mildly contingent on answer to #2.

Hosein Weekly updates

I am working with Andrew Leong to derive more experimental results which can be adopted to validate our numerical simulations.

In addition, I am still working on single crystal quartz simulations. We need more accurate fracture properties. I have searched in the literature but cannot find anyone who talked about the mode II fracture propagation in those materials.

I also started studying some papers about physical-based damage model, namely, Paliwal and Ramesh 2008 and Daphalapurkar et al 2011.


Alex Sun Weekly Update July 20th, 2016

  1. Last week I attended the ceramics summer meeting, which increases my understanding of the boron carbide material. I clarified my part of task in the whole project. Also, I talked to people from ARL and found that we shared a lot common research interests. Future cooperation will be continue after this.
  2. Reading papers and will give a presentation on group meeting.
  3. My summer plan is ultimately doing one or two PSPI on granular boron carbide. I am on my way to setup the experiments. I have tested the 600lp/mm grating and fixed the autocollimator. I gave the machineshop a deadline of next Tuesday to return all my parts. Powders from ARL will also arrive around that time and I can really start the experiment. I will do 2 PSPI tests before my fall term start.

Alex Sun Group Weekly Update

  1. Did the drop tower training with Matt. Have a basic idea of how the drop tower working and how to setup the camera with the machine. The drop tower itself if a good way of testing granular material.
  2. Reading some literature on granular flow. There are some papers on granular fabric tensor to describe the contact between grains in a micro mechanical way. This is a general direction for my theoretical modeling.
  3. Did some slides for presentation on ceramic meeting on Thursday.

Alex Sun Weekly Update July 5th 2016

(1) Doing literature review on ceramics modeling. The definition of damage tensor in terms of crack distribution gives me some inspiration on modeling. We can have granular tensor for the granular behavior of ceramics in a similarly way. This tensor will be part of my constitutive model. Like crack in damage tensor, physics law such as Mohr-Coloumb law should be included in local system. More generally, I will also try to define other material plasticity like amorphization and texture as the material mechanisms in this model. I am not sure whether dislocation mechanisms is activated for BC deformed at high level multi axial stress state. Ceramics mechanisms should be understood in order to come up with models for simulation or experimental data analysis.

(2) Did some fracture surface and fragmentation analysis on fragments and fractured Boron Carbide from Jeff using confocal Optical Microscopy. What is very interesting is I can get depth measurement of fracture surface and grain(fragments) size on vertical direction. More features can be obtained than planar images from SEM. Will continue on this. For a planar fragments size analysis, the traditional OM is enough to do the job.

(3) I am suppose to get my plate on July 15th. I will start my experiment setup formally from that time and to get the first PSPI data around Aug. 15th.