A 2D plane-strain dynamically propagating crack under tensile loading is simulated with cohesive elements. Information of the main crack is extracted from a diffuse crack network with the use of ...graph properties. Micro-transgranular fracture properties are calibrated by comparing the crack path transgranular fracture percentage of numerical simulations with experimental data. Results show that although weaker grain boundaries cause more deflections in the crack path and consequently increase the crack length and roughness, the overall toughness is decreased due to reduction of transgranular fracture. The main crack failure mode transition at grain boundaries is compared to static (Hutchinson and Suo, 1992) and dynamic (Xu et al., 2003) classical analytical predictions. It is observed that in many cases, before the arrival of a transgranular fracture at a grain boundary, a micro-daughter crack starts to propagate on the interface. The crack tip extension through this daughter crack/mother crack mechanism complicates the interpretation of the main crack speed in dynamic regime. Yet, the dynamic analysis brings a more accurate prediction of the crack path in microstructures compared to the static one when the data are segregated according to this mechanism.
We present the first results from the science demonstration phase for the Hi-GAL survey, the Herschel key program that will map the inner Galactic plane of the Milky Way in 5 bands. We outline our ...data reduction strategy and present some science highlights on the two observed 2° × 2° tiles approximately centered at l = 30° and l = 59°. The two regions are extremely rich in intense and highly structured extended emission which shows a widespread organization in filaments. Source SEDs can be built for hundreds of objects in the two fields, and physical parameters can be extracted, for a good fraction of them where the distance could be estimated. The compact sources (which we will call cores' in the following) are found for the most part to be associated with the filaments, and the relationship to the local beam-averaged column density of the filament itself shows that a core seems to appear when a threshold around AV ~ 1 is exceeded for the regions in the l = 59° field; a AV value between 5 and 10 is found for the l = 30° field, likely due to the relatively higher distances of the sources. This outlines an exciting scenario where diffuse clouds first collapse into filaments, which later fragment to cores where the column density has reached a critical level. In spite of core L/M ratios being well in excess of a few for many sources, we find core surface densities between 0.03 and 0.5 g cm-2. Our results are in good agreement with recent MHD numerical simulations of filaments forming from large-scale converging flows.
This paper presents an efficient method to implement a damage law within an explicit time-integration scheme, in an open-source object-oriented finite-element framework. The hybrid object/vector ...design of the framework and implementation choices are detailed in the special case of non-local continuum damage constitutive laws. The computationally demanding aspect of such constitutive laws requires efficient algorithms, capable of using High Performance Computing (HPC) clusters. The performance of our approach is demonstrated on a numerically and physically challenging 3D dynamic brittle-fragmentation test case. An almost perfect scalability is achieved on parallel computations. The global dynamics and energy terms are in good agreement with classical cohesive models’ predictions.
•New finite-element code based on a hybrid object/vector design.•Parallel implementation showing a close to perfect scalability on integral type localization limiter algorithms.•Results in agreement with theoretical predictions and comparable to other numerical approaches in terms of energies and fragments’ shapes are obtained with an explicit time-integration scheme and non-local continuum damage.
A direct multiscale method coupling molecular dynamics to finite element simulations is introduced to study the contact area evolution of rough surfaces under normal loading. First, a description of ...the difficulties due to using the bridging domain method at finite temperatures is discussed. This approach, which works well at low temperatures, is based on a projection, in an overlap region, of the atomic degrees of freedom on the coarser continuum description. It is shown that this leads to the emergence of a strong temperature gradient in the bridging zone. This has motivated the development of a simpler approach suitable for quasi-static contact problems conducted at constant but finite temperatures. This new approach is then applied to the normal loading of rough surfaces, in which the evolution of the real contact area with load is monitored. Surprisingly, the results show little influence of the contact area on temperature. However, the plastic events, in form of atomic reshuffling at the surface and dislocation activity, do clearly depend on temperature. The results show also a strong and temperature-dependent relaxation of the initial rough surfaces. This natural mechanism which alters atomic asperities brings to question the classical atomic description of roughness.
Socioeconomic status (SES) has been associated with differential healthcare outcomes and may be proxied using the area-deprivation index (ADI). Few studies to date have investigated the role of ADI ...on patient-reported outcomes and clinically meaningful improvement following lumbar spine fusion surgery.
The purpose of this study is to investigate the role of SES on lumbar fusion outcomes using Patient-Reported Outcomes Measurement Information System (PROMIS) surveys.
Retrospective review of a single institution cohort.
About 205 patients who underwent elective one-to-three level posterior lumbar spine fusion.
Change in PROMIS scores and achievement of minimum clinically important difference (MCID).
Patients 18 years or older undergoing elective one-to-three level lumbar spine fusion secondary to spinal degeneration from January 2015 to September 2021 with minimum one year follow-up were reviewed. ADI was calculated using patient-supplied addresses and patients were grouped into quartiles. Higher ADI values represent worse deprivation. Minimum clinically important difference (MCID) thresholds were calculated using distribution-based methods. Analysis of variance testing was used to assess differences within and between the quartile cohorts. Multivariable regression was used to identify features associated with the achievement of MCID.
About 205 patients met inclusion and exclusion criteria. The average age of our cohort was 66±12 years. The average time to final follow-up was 23±8 months (range 12-36 months). No differences were observed between preoperative baseline scores amongst the four quartiles. All ADI cohorts showed significant improvement for pain interference (PI) at final follow-up (p<.05), with patients who had the lowest socioeconomic status having the lowest absolute improvement from preoperative baseline physical function (PF) and PI (p=.01). Only those patients who were in the lowest socioeconomic quartile failed to significantly improve for PF at final follow-up (p=.19). There was a significant negative correlation between socioeconomic level and the absolute proportion of patients reaching MCID for PI (p=.04) and PF (p=.03). However, while ADI was a significant predictor of achieving MCID for PI (p=.02), it was nonsignificant for achieving MCID for PF.
Our study investigated the influence of ADI on postoperative PROMIS scores and identified a negative correlation between ADI quartile and the proportion of patients reaching MCID. Patients in the worse ADI quartile had lower chances of reaching clinically meaningful improvement in PI. Policies focused on alleviating geographical deprivation may augment clinical outcomes following lumbar surgery.
We have used in situ X-ray scattering and finite element modeling (FEM) to examine the micromechanics of deformation of in situ formed metallic-glass–matrix composites consisting of Ta-rich particles ...dispersed in an amorphous matrix. The strain measurements show that under uniaxial compression the second-phase particles yield at an applied stress of ∼325
MPa. After yielding, the particles do not strain harden significantly; we show that this is due to an increasingly hydrostatic stress state arising from the lateral constraint on deformation of the particles imposed by the elastic matrix. Shear band initiation in the matrix is not due to the difference in elastic properties between the matrix and the particles. Rather, the development of a plastic misfit strain causes stress concentrations around the particles, resulting in localized yielding of the matrix by shear band formation at an applied stress of ∼1450
MPa, considerably lower than the macroscopic yield stress of the composite (∼1725
MPa). Shear bands do not propagate at the lower stress because the yield criterion of the matrix is only satisfied in the region immediately around the particles. At the higher stresses, the yield criterion is satisfied in large regions of the matrix, allowing extensive shear band propagation and significant macroscopic plastic deformation. However, the presence of the particles makes the stress state highly inhomogeneous, which may partially explain why fracture is suppressed in the composite, allowing the development of large plastic strains.
We present three-dimensional finite-element simulations showing the propagation of slip fronts at striped heterogeneous interfaces. The heterogeneous area consists of alternating stripes of weaker ...and stronger frictional properties, which is equivalent to a lower and higher fracture energy, respectively. By comparing the slip front propagation at interfaces that differ solely by the length scale of the heterogeneous pattern, we illustrate that two different propagation regimes exist. Interfaces with wide stripes present slip fronts with propagation speeds that transition from sub-Rayleigh to inter-sonic. Thinner stripes are, however, characterized by the propagation of sub-Rayleigh slip fronts, which are preceded by slip pulses of negligible slip in the weaker stripes. From a macroscopic point of view, an interface with a smaller heterogeneous pattern appears to be stronger than the equivalent coarser interface even though both have the same average properties. The numerical results as well as a theoretical approach based on fracture-mechanics considerations suggest that the origin of these two distinct propagation mechanisms lies in the interaction between the length scales of the cohesive zone and the heterogeneous configuration. We further show by estimating the relevant length scales that the occurring propagation mechanism is influenced by the friction weakening rate of the interface as well as the shear modulus of the bulk material.
A two-dimensional finite element model is developed to investigate intergranular fracture in alumina under compression. The grain interiors are modeled as anisotropic elastic and the properties of ...the grain boundaries are fitted from experimental data. Material failure is found to occur by the linking of wing cracks. The effect of confinement pressure on the strength and strain to failure is investigated. Confinement pressure is shown to have a weak effect on the total fracture surface at failure, but is found to have a strong effect on microcrack coalescence. The numerical model suggests that the size of the largest microcrack cluster or the variance of microcrack length could be a useful criterion for predicting impending catastrophic failure.
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