A Study of the Radial Compressive Cracking Force of Two Cassava Varieties

Radial compressive cracking force of two cassava varieties （TMS 30572 and TMS 4（2）1425） was determined. Tubers from plants about 1.5 years old, freshly harvested from the Teaching and Research Farm of Obafemi Awolowo University, Ile-Ife, Nigeria, were used for this study. The tubers were cleaned and sliced into different lengths ranging from 25 mm to 150 mm in steps of 25 mm. For each species, slices of a particular length were sorted into 8 diameter groups： 21-30, 31-40, 41-50, 51-60, 61-70, 71-80, 81-90 and 91-100 ram. The cracking force of the sliced tubers was determined using an adapted tensometer. Generally, the cracking force increases with increase in tuber slice length. While the average value across all diameters ranges from 504.65 N to 1,770.19 N as the tuber length varies from 25 mm to 150 mm for TMS 30572, it ranges from 428.32 N to 1,721.95 N for TMS 4（2）1425. Within the same diameter group, the compression cracking force for tubers of small lengths was significantly lower than that required for large tuber lengths. Further, while the average cracking force for TMS 30572 varies between 894.54 N and 1,287.16 N across varying diameter ranges, it varies between 715.47 N and 1,268.82 N for TMS 4（2）1425. The highest values for both varieties occur at diameter range 71-80 mm. The data generated would be useful for the development of an efficient cassava peeling machine, based on the principle of peel-flesh separation by compression and peel removal with knives.

NUMERICAL SIMULATION OF STRESS-STRAIN DISTRIBUTIONS FOR WELD METAL SOLIDIFICATION CRACKING IN STAINLESS STEEL

This paper analyzed the characteristics of welding solidification crack of stainless steels,and clearly re- vealed the the of the deformation in the molten - the pool and the solidification shrinkage on the stress - strain fields in the trail of molten - weld pool.Moreover, rheologic properties of the alloys in solid - liquid zone were also obtained by measuring the hading and unloading deform curves of the steels.As a result, a numerical model for simulation of stress - strain distributions of welding solidifi- cation crack was developed. On the basis of the model,the thesis simulated the driving force of solidifi- cation crack of stainless steels, that is, stress - strain fields in the trail of molten-weld pool with fi- nite element method.

Nonequilibrium Statistical Nature of Intergranular Brittle Fracture in Polycrystal

The brittle fracture probability and reliability are obtained in terms of dislocation mechanism of microcrack evolution. The statistical distribution functions and statistical deviations of elongation, strength, plastic work, crack extension force, fracture foughness, critical and crack length, can be derived in a unified fashion.

Stress/strain distributions for weld metal solidification crack instain less steels

This paper has simulated the driving force of solidification crack of stainless steels, that is, stress/strain field in the trail of molten pool. Firstly, the effect of the deformation in the molten pool was eliminated after the element rebirth method was adopted. Secondly, the influence of solidification shrinkage was taken into account by increasing thermal expansion coefficients of the steels at elevated temperatures. Finally, the stress/strain distributions of different conditions have been computed and analyzed. Furthermore, the driving force curves of the solidification crack of the steels have been obtained by converting strain time curves into strain temperature curves, which founds a basis for predicting welding solidification crack.

ANALYSIS ON THE COHESIVE STRESS AT HALF INFINITE CRACK TIP

The nonlinear fracture behavior of quasi-brittle materials is closely related with the cohesive force distribution of fracture process zone at crack tip. Based on fracture character of quasi-brittle materials, a mechanical analysis model of half infinite crack with cohesive stress is presented. A pair of integral equations is established according to the superposition principle of crack opening displacement in solids, and the fictitious adhesive stress is unknown function . The properties of integral equations are analyzed, and the series function expression of cohesive stress is certified. By means of the data of actual crack opening displacement, two approaches to gain the cohesive stress distribution are proposed through resolving algebra equation. They are the integral transformation method for continuous displacement of actual crack opening, and the least square method for the discrete data of crack opening displacement. The calculation examples of two approaches and associated discussions are given.

Structural Integrity Assessment of Welded Pressure Vessel Produced of HSLA Steel

Welded joint is a critical region of a welded structure.The operational safety of welded pressure equipment mostly depends on the behaviour of loaded weldments.Safety of welded structure is dependent on the properties of welded joint as whole and of its constituents (parent metal,heat affected zone and weld metal).In this paper the behaviour of welded joint cracked constituents is considered.Structural integrity assessment procedure is applied to welded pressure vessel produced of high-strength low-alloyed steel,operating at-40°C,comparing crack driving force and material crack resistance,using path-independent contour J-integral as fracture mechanics parameter.The comparison of crack driving force,expressed by J-integral and material resistant curve,J-R curve,provide the possibility to determine the extent of the stable crack as well as the critical crack size for its final fast propagation and also to assess the structural integrity of a cracked pressure vessel.