Shi Fan Zhu

An Experimental-Numerical Hybrid Method to Determine Dynamic Elastic-Plastic Fracture Toughness

The dynamic fracture behavior of 7075-T6 aluminum alloy was studied by finite element method to simulate a cracked three-point bending specimen loaded by stress wave loading. In order to determine the elastic-plastic dynamic fracture toughness using quasi-static fracture mechanics theory, the nominal load measured by Hopkinson pressure bar loaded fracture testing system was input into a finite element program to calculate the loading point displacement, and then this displacement was employed to obtain the load-displacement field in the vicinity of the crack tip without the inertia effect, the variation of J-integral as a function of time was established using the load-displacement parameters determined by finite element analysis. The critical J-integral corresponding to crack initiation time detected by a small strain gauge mounted on the three-point bending fracture specimen is determined as an elastic-plastic dynamic fracture toughness (JId). The comparison between the equivalent dynamic fracture toughness(KId) given by the aforementioned procedures and the value measured in previous studies was made to verify the validation of the proposed procedure.

Structural Design and Finite Element Analysis of Composite Wind Turbine Blade

This paper presents structural studies of a medium scale composite wind turbine blade construction made of epoxy glass fiber for a 750kW rated power stall regulated horizontal axis wind turbine system. The complex geometry of the blade with a skin-spar foam sandwich structure was generated by utilizing commercial code ANSYS finite element package. Dimensions of twist, chord and thickness were developed by computer program. NREL S-series airfoils with different chord thickness are used along current blade cross-sections. The current design method uses blade element momentum (BEM) theory to complete satisfactory blade design and can be carried out using a spreadsheet, lift and drag curves for the chosen aerofoil. According to composite laminate theory and finite element method, optimal blade design was obtained. The focus is on the structural static strength of wind turbine blades loaded in flap-wise direction and methods for optimizing the blade cross-section to improve structural reliability. Moreover, the natural frequencies and modal shapes of the rotor blade were calculated for defining dynamic characteristics. Structural analysis was performed by using the finite element method in order to evaluate and confirm the blade to be sound and stable under various load conditions.

An Ontology-Based Framework for Ergonomics Knowledge Classification and Representation

Ergonomics applications is now a highlight spot in various fields. To tackle the problem of unsustainable accumulation of ergonomics knowledge, the representation of ergonomics knowledge is of great importance for the ergonomics experts system to be developed. Based on the appropriate ontology technology, the general knowledge of ergonomics is reclassified to the man-machine-environment. By adopting the top-down method and Protégé, an ontology-based ergonomic framework is conducted to the ergonomics knowledge classification and representation.

Analyzing the Effects of the Hollow Bars on Compression Experimental Setup Using Numerical Methods

For the Comprehension of the dynamic mechanical properties of the materials under the dynamic loading, Hopkinson pressure bar apparatus is used. During the compression testing of the low impedance materials the use of the hollow transmission bar is common. In the current work, the analysis is performed to analyze the effects of hollow transmission and incident bars on the specimen testing for the large diameter compression setup. Complete model of the setup is prepared using the ANSYS software and the simulation of loading is done using the LS-DYNA software. The results of analysis indicate that for the large compression testing setup, solid bars can be replaced with hollow bars. By using the hollow transmission bar the objective of high strain rate testing is also obtained.

The Influence of Wedge Shape on the Determination of Dynamic Fracture Toughness in SHPB Test

The SHPB loading three-point bending specimen is a popular way for measuring the dynamic fracture toughness of the material. The wedge shapes on the loading end of the incident bar have necessary effects on the propagation of the stress wave. The dynamic mechanical response and the fracture toughness of the aluminum alloy were measured by SHPB with different wedge shapes, and the influences of wedge shape on determination of dynamic fracture toughness was analyzed in this study. The investigation result can be used to provide reference for the design of a new Hopkinson apparatus for dynamic fracture testing.

Importance of Material’s Dynamic Stress Intensity Factor Calculation in the Design of High Strenght Structures

The researchers and scientists have concluded that material dynamic fracture properties must be considered during the design stage of the modern structure. The dynamic stress intensity factor is very important in understanding of material dynamic behavior. Keeping in view the importance of the materials dynamic stress intensity factor: an efficient and reliable numerical-analytical procedure is developed for calculation of dynamic stress intensity factor. For this, three-dimensional model of a Modified Hopkinson Pressure Bar (MHPB) and a specimen is modeled and analyzed with the ANSYS software. Transient dynamic analysis technique is used for simulation of load-variations as a function of time. As an output of analysis, values of load point displacement and Crack Mouth Opening Displacement (CMOD) are obtained. These values are substituted into two different analytical formulas for calculation of a dynamic stress intensity factor. The results obtained are compared with previous published results, and a good agreement is found.

Analyzing Stress Wave Propagation in a Hollow Bar Loaded Three-Point Bend Fracture Test Using Numerical Methods

Modified Hopkinson pressure bar apparatus is widely used to investigate the dynamic fracture behavior of materials at higher rate loading. While using a small sample for fracture toughness testing, plane strain conditions are compromised. In the current work, a large diameter two-bar/ three-point bend fracture setup is used to analyze stress wave propagation behavior within a larger cracked specimen. The experimental setup model consists of striker, incident bar, loading pin, cracked three-point specimen, span and transmission bar. The model is prepared using ANSYS software and the transient dynamic analysis technique is used to simulate the dynamic load. The effects of increased transient time on the stress wave propagation behavior within the cracked sample and the stress and strain values at the crack tip of the three-point bend specimen are analyzed. In addition, the effects of the hollow striker, the hollow incident bar and the specimen span are studied. It is found that during large specimen testing, an increase in the transient time results in the lower stress and strain values in the specimen crack-tip. The relationship of the specimen span, the striker and the incident bars with the strain values in the specimen is analyzed and a method for the three-point bend specimen testing at the higher strain rates is also proposed.

Contact State Investigation of a Three-Point Bend Specimen Using Numerical Methods

At higher loading rates, modified Hopkinson pressure bar apparatus is widely used to determine the dynamic fracture toughness of the engineering materials. For accurate measurement of the dynamic fracture properties, we need to thoroughly understand the contact situation of the three-point bend specimen, with the loading apparatus. Strong inertial effects complicate the specimen’s contact situation with impactor and supports. In this work, ANSYS software is used for modeling and analysis of a modified Hopkinson pressure bar loaded fracture experimental setup. Analysis of stress contours and nodal displacements are used for the examination of specimen contact state. The results indicate that during loading in the elastic range, the specimen remains in contact with the loading apparatus as this is previously proved experimentally.

Fundamental Concepts and Principles for Robust Structures, Subjected to Dynamic Loading

The dynamic behavior assessment of material is very important before selecting the material for structural applications. In the modern world, Modified Hopkinson pressure bar apparatus is being widely used to investigate the dynamic behavior of engineering materials under compressive and tensile loading. Materials like ceramics, rocks, metals, concrete and soft material are being tested. The cost associated with the dynamic loading pressure bar apparatus are also low and can be easily built. For accurate measurement of material properties we need to understand the basic concepts associated with dynamic loading. With the advancement in computational capabilities, the dynamic load testing of materials is also performed in available commercial softwares. In the current work, the basic concepts and components associated with dynamic compressive loading system are discussed and a test case studies are also selected for analyzing material specimen behavior during testing. For simulation of dynamic compressive loading ANSYS LS-DYNA software is used and the output of the simulation results is analyzed. The effects of changing the diameter of material specimen, and hollow bars on stress and strain values in the bar and setup are also discussed.

Design Optimization of Hub for 3-Bladed Horizontal Axis Tidal Turbine

In this paper, Wind turbines knowledge, which is already matured enough, is effectively used for design of horizontal axis tidal turbine (HATT) hub. Design optimization keeping in view the shape and strength for minimum weight was done using ANSYS software. Maximum stress concentration areas are found to be the blade roots and edges of shaft connection. A novel approach is used to optimize the fillet radii along with overall thickness.