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The deformation behavior of metal lattice structures is extremely complex and challenging to predict, especially since strain is not uniformly distributed throughout the structure. Understanding and predicting the failure behavior for these types of light-weighting structures is of great interest due to the excellent scaling of stiffness- and strength-to weight ratios they display. Therefore, there is a need to perform simplified experiments that probe unit cell mechanisms. This study reports on high resolution mapping of the heterogeneous structural response of single unit cells to the macro-scale loading condition. Two types of structures, known to show different stress-strain responses, were evaluated using synchrotron radiation micro-tomography while performing in-situ uniaxial compression tests to capture the local micro-strain deformation. These structures included the octet-truss, a stretch-dominated lattice, and the rhombic-dodecahedron, a bend-dominated lattice. The tomographic analysis showed that the stretch- and bend-dominated lattices exhibit different failure mechanisms and that the defects built into the structure cause a heterogeneous localized deformation response. Also shown here is a change in failure mode for stretch-dominated lattices, where there appears to be a transition from buckling to plastic yielding for samples with a relative density between 10 and 20%. The experimental results were also used to inform computational studies designed to predict the mesoscale deformation behavior of lattice structures. Here an equivalent continuum model and a finite element model were used to predict both local strain fields and mechanical behavior of lattices with different topologies.

Signe S Risom,1,2 Johanne Lind,2 Pamela J McCabe,3 Selina Kikkenborg Berg1,4,5 1The Heart Centre, Rigshospitalet, Copenhagen University Hospital, Copenhagen, Denmark; 2Department of Nursing, Metropolitan University College, Copenhagen, Denmark; 3Mayo Clinic, Rochester, MN, USA; 4Faculty of Health and Medical Sciences, University of Copenhagen, Copenhagen, Denmark; 5National Institute of Public Health, University of Southern Denmark, Copenhagen, Denmark Purpose: The CopenHeartRFA trial was designed and conducted to explore the effects of rehabilitation on patients treated with ablation for atrial fibrillation (AF). It included a cardiac rehabilitation program consisting of physical exercise and psychoeducational consultations over 6 months. As part of the evaluation of the CopenHeartRFA trial, both quantitative and qualitative data were collected. The intervention was delivered by a multidisciplinary team. Aim: This study aimed to understand the experience of patients treated for AF with ablation who participated in the CopenHeartRFA cardiac rehabilitation program. Methods: A qualitative descriptive design was used. A purposive sample of 10 patients who had completed the intervention consented to participate. The interviews were conducted face-to-face and were audio-recorded and transcribed. Qualitative content analyses were used to analyze the data. The interviews were analyzed individually by two researchers and themes were constructed and discussed. Results: The sample included 10 participants, mean age 54.6 years. Four categories were identified and labeled: 1) strengthening belief in one’s own physical capacity and survival; 2) still struggling with fear of AF symptoms; 3) a need for support to move on; and 4) regaining confidence in one’s own mental strength with support from professionals. Conclusion: The four themes describe a positive experience from participating in the rehabilitation program. The rehabilitation program promoted self-efficacy for engaging in physical activity and the benefit of a safe environment for processing the emotional responses and the value of the therapeutic relationship between the patient and the rehabilitation provider. Keywords: atrial fibrillation, rehabilitation, qualitative research

Dynamic compaction of granular materials is a complex process, wherein the material response at the continuum scale arises from fracture, comminution, and fragment flow at the grain scale. Granular materials have heterogeneity due to variation in grain properties as well as variation in local packing density and structure. These heterogeneities may affect the dynamic compaction response, producing a structured and time-varying compaction front. The methodology used to characterize the shock behavior in solid materials may be inappropriate for granular materials because of this unsteady behavior and interactions between the granular material and measurement surfaces. To observe the compaction front heterogeneity, in situ x-ray imaging of granular compaction is conducted at a scale between the grain- and continuum scales. To allow for sufficient x-ray transmission, a thin sample geometry is used, for which boundary affects may result in a significantly different load path than would occur in a 1-D compaction configuration. Numerical simulations of the experimental geometry support the analysis of the results so that the feature of the compaction front can be distinguished from artifacts of the experimental configuration. The results suggest that compaction front heterogeneity may have structure with a length scale of tens of particle diameters and demonstrate that finite grain size can inhibit the formation of shear-induced features that would arise in a homogenized representation of the same material. [ABSTRACT FROM AUTHOR]