Fracture Mechanism and Fracture Toughness at the Interface Between Cortical and Cancellous Bone.

The microstructure at the interface of cortical and cancellous bone is quite complicated. The fracture mechanisms at this location are necessary for understanding the comprehensive fracture of the whole bone. The goal of this study is to identify fracture toughness in terms of J integral and fracture mechanism at the interface between cortical and cancellous bone. For this purpose, single edge notch bend (SENB) specimens were prepared from bovine proximal femur according to ASTM-E399 standard. Bone samples were prepared such that half of the sample width consists of cortical bone and other half of the width was cancellous bone; this interfacial bone is referred as a corticellous bone. Elastic-plastic fracture mechanics was used to measure fracture toughness. The J integral (both elastic and plastic) was used to quantify the fracture toughness. The plastic part of J integral value (Jpl) of corticellous specimen was 9310 J m-2, and shown to be 27 times of the J integral of the elastic part (Jel), 341 J m-2. The total J integral of the corticellous bone was found to be 9651 J m-2, which is close to two times of the cortical bone, 4731 J m-2. This study observed that J integral of corticellous bone is higher than the cortical bone since more energy is required for plastic deformation of corticellous bone due to crack branches and slowdown at the interface between cortical and cancellous bone.

Enhancing the sound transmission loss through acoustic double panel using sonic crystal and porous material.

Acoustic panels are widely used for sound insulation in various applications. Sound transmission loss (STL) through the panel is due to a change in acoustic impedance as sound travels from one medium to another. In double panels, STL further increases due to multiple reflections in air cavity. Recently the sonic crystal (SC) has emerged as an interesting research topic which provides sound attenuation in specific frequency bands. The present paper aims at combining the property of a SC with the acoustic panel for enhancing the STL through the double panel. Initially, an analytical method is developed to obtain the STL through the double panel. Further finite element (FE) simulations are performed using acoustic structure interaction to obtain the STL through the double panel which is in good agreement with the analytical predictions. The SC, along with the double panel, is analyzed using the FE method for the combined effect of both sound attenuators. Further, glass wool is considered as a filler material between the double panel as well as between the double panel and the SC assembly. It is found that the combined structure of the double panel and the SC with glass wool as filler gives the best STL for all different cases for the same external dimensions.

Metamaterial foundation for seismic wave attenuation for low and wide frequency band.

Metamaterials are periodic structures made by repeating a unit cell. Such a structure shows frequency-specific wave attenuation behaviour. In this work, a 2D metamaterial foundation is proposed for the seismic protection of buildings. The paramount challenge is to offer low frequency attenuation (~ 2-8 Hz), which is the dominant excitation during an earthquake. Based on the parametric study performed, a new type of metamaterial structure was proposed. It was found that the foundation consisting of repeating circular scatterers made of steel and plumbum embedded in rubber matrix can provide low and wide frequency wave attenuation from 2.6 to 7.8 Hz. The computational model of the structure was subjected to transient excitation against three pre-recorded earthquake excitations. The result showed that the novel foundation can resist the propagation of the seismic wave to the structure. Further, the response of a 2D building frame with metamaterial foundation was compared to a concrete foundation exposed to different earthquake excitations. The results are very promising as the frame vibration on the metamaterial foundation was significantly less than the same frame on the concrete foundation. The presented work opens the path to new research and development of seismic metamaterial foundation for earthquake attenuation.

Experimental and numerical comparisons between finite element method, element-free Galerkin method, and extended finite element method predicted stress intensity factor and energy release rate of cortical bone considering anisotropic bone modelling.

Stress intensity factor and energy release rate are important parameters to understand the fracture behaviour of bone. The objective of this study is to predict stress intensity factor and energy release rate using finite element method, element-free Galerkin method, and extended finite element method and compare these results with the experimentally determined values. For experimental purpose, 20 longitudinally and transversely fractured single-edge notched bend specimens were prepared and tested according to ASTM standard. All specimens were tested using the universal testing machine. For numerical simulations (finite element method, element-free Galerkin method, and extended finite element method), two-dimensional model of cortical bone was developed by assuming plane strain condition. Material properties of the cortical bone were considered as anisotropic and homogeneous. The values obtained through finite element method, element-free Galerkin method, and extended finite element method are well corroborated to experimentally determined values and earlier published data. However, element-free Galerkin method and extended finite element method predict more accurate results as compared to finite element method. In the case of the transversely fractured specimen, the values of stress intensity factor and energy release rate were found to be higher as compared to the longitudinally fractured specimen, which shows consistency with earlier published data. This study also indicates element-free Galerkin method and extended finite element method predicted stress intensity factor and energy release rate results are more close to experimental results as compared to finite element method, and therefore, these methods can be used in the different field of biomechanics, particularly to predict bone fracture.

Erdheim-Chester disease: a unique presentation with liver involvement and vertebral osteolytic lesions.

Erdheim-Chester disease is a very rare xanthogranulomatous, non-Langerhans cell systemic histiocytosis with an unknown etiology and pathogenesis. Histologically, it is characterized by a diffuse infiltration with large, foamy histiocytes, rare Touton-like giant cells, lymphocytic aggregates, and fibrosis. The histiocytes differ from the Langerhans cell group in ontogenesis, immunohistochemistry (positive for CD68 and negative for CD1a and S100 protein), and ultrastructural appearance (lack of Birbeck granules). Although most of the cases have symmetric osteosclerosis of the long bones, an involvement of the axial skeleton has also been described. Extraskeletal lesions are present in more than 50% of the patients and may involve the retroperitoneal space, lungs, kidneys, brain, retro-orbital space, and heart. This study presents the case of a patient with Erdheim-Chester disease with vertebral destruction and, for the first time, to our knowledge, involvement of the liver. The diagnosis is based on radiologic, histologic, immunohistochemical, and ultrastructural findings.