3 research outputs found
Characterizing the mechanical response of metallic glasses to uniaxial tension using a spring network model
Metallic glasses are frequently used as structural materials. Therefore, it
is important to develop methods to predict their mechanical response as a
function of the microstructure prior to loading. We develop a coarse-grained
spring network model, which describes the mechanical response of metallic
glasses using an equivalent series network of springs, which can break and
re-form to mimic atomic rearrangements during deformation. To validate the
model, we perform simulations of quasistatic, uniaxial tension of Lennard-Jones
and embedded atom method (EAM) potentials for CuZr metallic
glasses. We consider samples prepared using a wide range of cooling rates and
with different amounts of crystalline order. We show that both the
Lennard-Jones and EAM models possess qualitatively similar stress
versus strain curves. By specifying five parameters in the spring
network model (ultimate strength, strain at ultimate strength, slopes of
at and at large strain, and strain at fracture
where ), we can accurately describe the form of the stress-strain
curves during uniaxial tension for the computational studies of
CuZr, as well as recent experimental studies of several Zr-based
metallic glasses. For the computational studies of CuZr, we find
that the yield strain distribution is shifted to larger strains for slowly
cooled glasses compared to rapidly cooled glasses. In addition, the average
number of new springs and their rate of formation decreases with decreasing
cooling rate. These effects offset each other at large strains, causing the
stress-strain curve to become independent of the sample preparation protocol in
this regime. In future studies, we will extract the parameters that define the
spring network model directly from atomic rearrangements that occur during
uniaxial deformation.Comment: 16 pages, 13 figure
Avalanche Statistics from Data with Low Time Resolution
Extracting avalanche distributions from experimental microplasticity data can be hampered by limited time resolution. We compute the effects of low time resolution on avalanche size distributions and give quantitative criteria for diagnosing and circumventing problems associated with low time resolution. We show that traditional analysis of data obtained at low acquisition rates can lead to avalanche size distributions with incorrect power-law exponents or no power-law scaling at all. Furthermore, we demonstrate that it can lead to apparent data collapses with incorrect power-law and cutoff exponents. We propose new methods to analyze low-resolution stress-time series that can recover the size distribution of the underlying avalanches even when the resolution is so low that naive analysis methods give incorrect results. We test these methods on both downsampled simulation data from a simple model and downsampled bulk metallic glass compression data and find that the methods recover the correct critical exponents
Universal Slip Dynamics in Metallic Glasses and Granular Matter – Linking Frictional Weakening with Inertial Effects
Slowly strained solids deform via intermittent slips that exhibit a material-independent critical size distribution. Here, by comparing two disparate systems - granular materials and bulk metallic glasses - we show evidence that not only the statistics of slips but also their dynamics are remarkably similar, i.e. independent of the microscopic details of the material. By resolving and comparing the full time evolution of avalanches in bulk metallic glasses and granular materials, we uncover a regime of universal deformation dynamics. We experimentally verify the predicted universal scaling functions for the dynamics of individual avalanches in both systems, and show that both the slip statistics and dynamics are independent of the scale and details of the material structure and interactions, thus settling a long-standing debate as to whether or not the claim of universality includes only the slip statistics or also the slip dynamics. The results imply that the frictional weakening in granular materials and the interplay of damping, weakening and inertial effects in bulk metallic glasses have strikingly similar effects on the slip dynamics. These results are important for transferring experimental results across scales and material structures in a single theory of deformation dynamics