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The fracture behaviors of tungsten alloys 91W-6.3Ni-2.7Fe were investigated by tensile tests and numerical simulations. Firstly, tensile tests were conducted on the S-570 SEM with an in-situ tensile stage. With this system, the process of deformation, damage and evolution in micro-area can be tracked and recorded, and at the same time, the load-strain curve can be drawn. Secondly, the 2D finite element model of a unit cell for the tungsten alloys was established by using finite element program. By copying the unit cell model, the macro-model of the alloys was given. Dozen of cases were performed to simulate the fracture behaviors of tungsten alloys. Thirdly, the random model of the alloys was established. The fracture patterns of the alloys were investigated by the model. The interface between the tungsten particle and the matrix was explored in details. The effect of interface strength on the fracture patterns of the alloys was taken into account. A good agreement was achieved between the experimental results and the numerical predictions.

In this paper, the copper (Cu)-based multi-wall carbon nanotube (MWCNT) composite tools were fabricated using electro-co-deposition method. The composite tools were prepared from different MWCNT concentrated (0.5, 0.75 and 1g/L) electrolytic solution and these tools were utilized in electro discharge machining (EDM). The experiments were performed with varying discharge currents. The results indicated that the incorporation of MWCNTs into the copper matrix greatly influenced the machining performances. A lower rate of tool wear and higher material removal rate (MRR) were observed for the copper-based MWCNT composite tools at different discharge currents. The highest tool wear rate (TWR) was reduced by 45.68% and the MRR was improved by 63% for the Cu-MWCNT (0.5g/L) composite tool compared to copper coated tool. At higher discharge current, smoother machined surfaces were generated using copper-based MWCNT composite tools compared to the copper tools. The SEM image exhibits that the micro-crack-free machined surfaces were produced by using copper-based MWCNT composite tools. The migration of tool material to the machined surface was also reduced for copper-based MWCNT composite tools.

The Direct FE² method is a recently developed concurrent multi-scale simulation approach with a monolithic solution scheme, where the macroscopic and microscopic models are solved in a unit iteration process. The conventional Direct FE² using quadrilateral element has some limitations in determining the failure state of a macro-element. In this work, we develop a new Direct FE² method based on the Single-integration Point triangle element (Direct SP-FE²) and apply it to simulate the micro-crack-induced fracture problems for the first time. The cohesive element is inserted into a representative volume element (RVE), so that the failure process of a macro-element can be determined by the micro-crack propagation on RVE. Accordingly, the relationship between macro-deformations and microstructures can be established directly, thus avoiding complex derivation and utilization of a multi-scale damage constitutive model. In Direct SP-FE², the failure state of a macro-element can be directly predicted by the RVE at the single-integration point inside, avoiding the uncertainty associated with predictions by multiple RVEs. As a result, compared to the conventional Direct FE² with a quadrilateral element, the Direct SP-FE² shows advantages in capturing complex geometric boundaries and predicting the damage evolution process and failure state more accurately. Various numerical examples are conducted to comprehensively validate the effectiveness of the present method in describing the influence of micro-cracks on macro-structure deformations. For the macro-damage behaviors, the simulation results by the Direct SP-FE² show good agreement with the direct numerical simulation (DNS) results of the full FE model at a significantly lower computational time. With the developed Direct SP-FE², a variety of complex micro-crack fracture problems in composite materials can be successfully modeled by manipulating the interior RVE structure.

A new method applied to test direct shear is developed and tested on sandstone with a constant normal load. A CCD camera and stereomicroscope were employed to record crack fractures of specimen surfaces and rock damage was recorded by an acoustic emission monitoring system. During the shearing process, AE signal changes were found to indicate crack initiation and propagation on the surface of specimens. Micro-cracks were observed on the specimen surfaces, including different genesis tension cracks, shear cracks, and rock bridges. Crack growth both along and through particles was clearly observed.

The fracture behaviors of tungsten alloys 91W-6.3Ni-2.7Fe were investigated by tensile tests and numerical simulations. Firstly, tensile tests were conducted on the S-570 SEM with an in-situ tensile stage. With this system, the process of deformation, damage and evolution in micro-area can be tracked and recorded, and at the same time, the load-strain curve can be drawn. Secondly, the 2D finite element model of a unit cell for the tungsten alloys was established by using finite element program. By copying the unit cell model, the macro-model of the alloys was given. Dozen of cases were performed to simulate the fracture behaviors of tungsten alloys. Thirdly, the random model of the alloys was established. The fracture patterns of the alloys were investigated by the model. The interface between the tungsten particle and the matrix was explored in details. The effect of interface strength on the fracture patterns of the alloys was taken into account. A good agreement was achieved between the experimental results and the numerical predictions.