Fusulinidæ of North China

[A general survey of Fusulinidæ species and their distribution in North China.

The geology of China

CONTENTS INTRODUCTION SECTION I Physiography. Chapter I General physiographical description of China proper. Chapter II Description of the several physiographical regions. Chapter III Geo-morphology. SECTION II. General geology. CHAPTER IV Stratigraphy. Introductory. Pre-cambrian. Cambrian-middle ordovician. Silurian-devonian. Carboniferous-permian. Triassic-jurassic. Post jurassic. Chapter V Igneous rocks in China. Chapter VI General geological structure of China. Chapter VII The geological history of China. SECTION III Economic geology Chapter VIII The economic aspect of Chinese geology. A. Coal fields. B. Oil fields. C. Ore deposits. D. Underground water. E. Miscellaneous Economic products

On Predicting Forming Limits Using Hill\u27s Yield Criteria

The analysis of localized necking is strongly dependent on the yield function. To predict forming limits, therefore, numerous yield criteria have been postulated to characterize the plastic deformation of sheet materials. Among them Hill\u27s 1948 and the fourth form of 1979 yield criteria are the most commonly used. A new yield criterion was proposed by Hill in 1993. It uses five independent and easily obtainable material parameters, which makes it flexible in representing the shape of the yield locus for different materials. The present investigation compares these three yield criteria in forming limit predictions based on both the Marciniak and Kuczynski (M-K) approach and the bifurcation analysis. It is observed that the M-K analysis based on Hill\u27s 1993 yield criterion provides forming limit predictions in agreement with experimental data. The bifurcation analysis based on Hill\u27s 1948 yield criterion also provides an acceptable prediction of forming limits for aluminum, although they are slightly higher. All three yield criteria are found to provide acceptable predictions for aluminum-killed (AK) steel based on the M-K method. For brass, only the prediction based on the M-K method and Hill\u27s 1993 yield criterion is close to the trend of experimental data

On predicting the forming limit diagram for automotive aluminium sheet

Aluminum has considerable potential as a material for automotive panels. The ability to predict forming limit diagrams accurately for aluminum is important for preventing failure in the forming process. A method is proposed to develop forming limits using Hill\u27s1993 yield criterion. Predicted limit strains based on both Hill\u27s 1948 and 1993 yield criterion are compared with experimental data for Aluminum 6111-T4. It is found that Hill\u27s 1993 yield criterion can characterize localized necking in aluminum sheets well, while Hill\u27s 1948 criterion cannot. The critical thickness rule is found useful in predicting the left hand side of FLDs

Effect of deformation-dependent material parameters on forming limits of thin sheets

Material properties are deformation history dependent. To take this fact into consideration in forming limit analysis, the material parameters are defined as functions of strain using the Voce equation. These history-dependent material parameters are incorporated in the M-K analysis based on Hill\u27s 1993 yield criterion in which all material parameters are independent, so that the effect of each of these history-dependent parameters on forming limits can be investigated individually. The analysis shows that history-dependent material properties have a significant influence on forming limits. An increasing r-value will increase the limit strain under plane strain (FLD0), which is different from the traditional M-K analysis. Comparison of predicted results with experimental data illustrates that the consideration of history-dependent material properties can improve forming limit predictions considerably

Comparison of Hill\u27s yield criteria in forming limit predictions

The analysis of localized necking is strongly dependent on the yield function. Numerous yield criteria have been advanced to characterize the plastic deformation of sheet materials. Among them Hill\u27s 1948 and the fourth form of 1979 yield criteria are the most commonly used yield criterion. A new and user-friendly yield criterion was proposed by Hill in 1993, which uses five independent and easily-obtainable material parameters. The present investigation compares these three yield criteria in forming limit predictions based on the M-K approach. The M-K analysis based on Hill\u27s 1993 yield criterion yields forming limit predictions for aluminum in good agreement with experimental data. All three yield criteria are found to provide acceptable predictions for aluminum killed steel

Prediction of forming limit curves of sheet metals using Hill\u27s 1993 user-friendly yield criterion of anisotropic materials

A user-friendly yield criterion was proposed by Hill in 1993, which utilizes five independent material parameters in representing the yield locus. In the present investigation, an attempt is made to analyze forming limits in sheet metals based on this yield criterion and the M-K approach. Comparison of the predicted results with experimental data indicates that Hill\u27s 1993 yield criterion is able to characterize the localized necking of both aluminum and AK steel. A parametric study is carried out to investigate the influence of material parameters (r0, r90, σ0, σ90 and σb) on forming limits, which shows that the shape of the yield locus has a significant influence on limit strains. © 1998 Elsevier Science Ltd. All rights reserved

Analysis of forming limits using the hill 1993 yield criterion

Forming limits of thin sheets are investigated using a yield criterion recently proposed by Hill (1993). This criterion utilizes five independent material parameters, which can be determined from uniaxial and balanced biaxial experiments, to describe a wide range of material properties of sheet metals, including the anomalous behavior of aluminum. In the present work, a bifurcation analysis is pursued to predict the onset of localized necking in strain rate insensitive sheet materials. A detailed parametric study is then conducted to evaluate the effect of various material parameters on the positive minor strain side of the forming limit diagram. It is observed that limit strains are strongly dependent on the shape of the yield locus. Forming limits predicted using Hill’s 1993 yield criterion are compared with those predicted using Hill’s 1948 and 1979 criteria. Results from the bifurcation analysis are also compared with experimental observations, as well as the limit strain predictions based on the M-K analysis. © 1998 by ASME