Mechanical Properties and Failure Modes of Rock Specimens with Specific Joint Geometries in Triaxial Unloading Compressive Test

The effects of disconnected joints on the mechanical characteristics of rock masses are interesting and challenging aspects of rock mechanics. The prime objective of this study is to investigate the effect of joint orientations and joint connectivity rates on the strength, deformation, and failure mechanisms of rock specimens under unloading condition. To establish the relationships between different factors (confining pressure, joint orientation, and joint connectivity) and failure mechanisms, a series of triaxial unloading tests were performed. The results showed that the joint orientation had a more considerable effect than the joint connectivity on the strength and deformation of the specimens. Generally, three different types of failures were observed (i.e., shear, mixed, and split). Finally, Griffith’s theory was utilized to analyze the maximum tensile stress around the crack. The findings of this paper can also be used for practical engineering problems.

Interfacial Delamination of Inorganic Films on Viscoelastic Substrates

The performance of flexible/stretchable electronics may be significantly reduced by the interfacial delamination due to the large mismatch at the interface between stiff films and soft substrates. Based on the theory of viscoelasticity, a cracked composite beam model is proposed in this paper to analyze the delamination of an elastic thin film from a viscoelastic substrate. The time-varying neutral plane of the composite beam is derived analytically, and then the energy release rate of the interfacial crack is obtained from the Griffith's theory. Further, three different states of the crack propagation under constant external loadings are predicted, which has potential applications on the structural design of inorganic flexible/stretchable electronics.

CHARACTER DEVELOPMENT OF NATHANIEL FROM JONATHAN STROUD’S BARTIMAEUS TRILOGY: THE AMULET OF SAMARKAND

This research is aimed at studying about the character development of someone. The development character is based on a novel Bartimaeus Trilogy: The Amulet of Samarkand by Jonathan Stroud. The discussion of this research is limited to the analysis of Nathaniel’s character development as the main character.The study of character development of Nathaniel from ordinary little boy to ambitious boy is important in this story because he is the main character and to prove that someone’s personality changed because of his past. For this reason, an objective approach suggested by Abrams is applied in this research. The definition of character development by Griffith which is used as the reference is also used to know whether the dynamic characteristic of Nathaniel is in accordance with the theories suggested by Griffith. The Library research is used in collecting the data. It includes doing intensive reading on the novel and finding the evidences through the plot.By doing the analysis, it turns out that Nathaniel’s character has changed from ordinary to ambitious boy because of his past. This finding is actually in accordance with Griffith’s theory of dynamic characteristic.

FRACTURE MODELING AND CHARACTERIZATION OF ELASTOMERIC MATERIALS AND COMPOSITES FOR DESIGN APPLICATIONS

Existing approaches of fracture analysis of elastomeric materials are primarily based on classical Griffith's theory of crack growth. There are numerous experimental, analytical, and computational studies covering applications of these approaches for a wide range of different polymeric materials, loading and environmental conditions, methods of testing and modeling, and so on. However, these results are usually based on certain assumptions regarding original cracks (their sizes, shapes, locations, etc.); that is, damage initiation is considered as the input of such analysis rather than the output. To avoid this challenge, an advanced approach predicting both (a) damage initiation and (b) damage growth is considered in this study for analysis of hyperelastic materials such as rubber and elastomeric composites. The approach is specifically proposed for finite element analysis implementation and is based on so-called cohesive elements. Such elements mimic contact between individual elements and account for both material strength and toughness properties. Implementation of the approach for hyperelastic deformation is considered in detail. Presented examples illustrate computational efficiency and benefits of the approach for design applications. Challenges and opportunities of material characterization for the approach are discussed as well.

FAILURE ASSESSMENT OF UHTC PLATE UNDER ELEVATED TEMPERATURE

In the present study, a theoretical model is presented to assess the failure temperature for ultra-high temperature ceramics (UHTCs). Unlike traditional thermal shock theory, the parameters, such as thermal expansion coefficient and Young's modulus, are considered a function of temperature in the present model. The oxide film of UHTCs is also believed to grow under high temperature. Considering two kinds of conditions, the critical elevated temperature for delamination is calculated using Griffith's theory. By establishing the relation between temperature and the mechanical properties of UHTCs, it is found that the failure behavior of UHTCs is strongly affected by the oxide film thickness, initial temperature and the heating rate.

The synergistic effect of dope concentration and jetdrawing on structure development of wet-spun poly(acrylonitrile)

Acrylic fibers are the major precursor of carbon fibers. In this work, the synergistic effect of polymer concentration and jet stretching on porosity, morphology and mechanical properties of wet-spun poly(acrylonitrile) fibers were studied and then the role of void size was elucidated. The results showed that the effect of jet stretching on fiber porosity is negligible below a threshold polymer concentration. Increasing polymer concentration up to 20 vol. % reduced the total porosity significantly but increased the nanometric void population slightly. On the other hand increasing polymer concentration and jet stretching simultaneously, improved mechanical properties as a result of a remarkable reduction in porosity. In addition, stretching shifted nanovoids distribution strongly toward smaller sizes. This was attributed to the effect of stretching and increasing polymer concentration on reducing the diffusion coefficient. Young's modulus of fibers also increased with decreasing overall porosity. Finally, strength-diameter correlation showed a good agreement with the Griffith's theory.

Prevention of Thin Film Failures for PECVD Amorphous-Si on Plastic Substrate

Amorphous silicon thin films were deposited below 160oC on PES plastic films using PECVD. After thin film deposition using PECVD, thin film failures such as film delamination and cracking often occurred. For successful growth of thin films (about 2000 Å) without their failures, it is necessary to solve the critical problem related to the internal compressive stress (some GPa) leading to delamination at a threshold thickness value of the films. The Griffith’s theory explains the failure process by looking at the excess of elastic energy inside the film, which overcomes the cohesive energy between film and substrate. In this work, reducing a-Si layer film thickness and optimizing a barrier SiNx layer have produced stable a-Si films at 150oC, over PES substrates.