Papers by Author: Jordi Jorba

Abstract: Young’s modulus varies with crystallographic orientation, temperature and alloying, but also with cold working and heat treatment. In this work, the evolution of Young’s modulus in polycrystalline pure aluminium (99.5%) with different cold-working levels determined at room temperature is presented. The deformation process was carried out in a universal tension machine and measurements were performed by ultrasounds. The Young’s modulus diminished from 70 to 65 GPa for 0-5% of deformation (elongation) and then increased with successive cold-working (68 GPa for 8.5% of elongation). These values were obtained 8 hours after plastic deformation was applied. This behaviour is compared with the Young’s modulus determined by extensometry in the same material. In this case, the modulus decreased from 70 to 63 GPa (3.5% of elongation) and then increased until 68 GPa for 10% of elongation. Results obtained on pure iron (Armco) deformed in the same conditions are included for comparative purposes. Values of Young’s modulus measured during the springback process after plastic deformation at different level are also included. Values obtained are between 10-15% lower than those measured 8 hours after plastic deformation.

Abstract: The information in the basic references about the relation between elastic constants and particularly Young’s modulus (E) behavior and plastic deformation indicates that this parameter is constant or almost constant. At the beginning of the XX century several authors indicated that E of some metals decreased when cold deformation increased and detected reductions up to 15% in steels, aluminum, copper, brass... In the last years this behavior is taking into account during the finite-element analysis of sheet metal stamping or other plastic deformation processes. This work includes an extensive review of papers of our research team and of other authors related with the behavior of Young’s modulus during plastic deformation of some metallic alloys. This parameter can diminish up to 10% by plastic deformation (tension test) in iron, aluminum, and stainless steel (UNS S 30403) but remains practically unaltered in aluminum alloys deformed before or after aging. Results of Young’s modulus in nanostructured copper and copper alloys determined by ultrasonic technique are also presented. Additional results of Young’s modulus of UNS G10180 and UNS G10430 steels measured during loading and unloading steps in tension test are also included. High differences in the E values were detected between both steps.

Abstract: Measurements of the elasticity modulus and Poisson’s ratio on nanostructured iron obtained by mechanical milling and on nanostructured copper obtained by severe plastic deformation (ECAP) have been carried out. Iron powder was severely deformed in a planetary ball milling. Powder compaction was done in a testing machine, obtaining cylinders that were compacted at temperatures between 425°C and 500°C. Commercial Cu of 99.98 wt % purity was processed at room temperature by Equal-Channel Angular Pressing (ECAP) following the route Bc. Heavy deformation was introduced in the samples after a considerable number of ECAP passes, from 1 to 16. A significant grain refinement was observed after processing the samples. The most important microstructural and mechanical changes were introduced in the first ECAP pass. Elasticity modulus and Poisson’s ratio were determined in iron and copper samples by ultrasonic measurement using an ultrasonic pulser-receiver and two transducers appropriate to the tested materials for pulse-echo sound velocity measurement in longitudinal and shear modes.

Abstract: The knowledge of some mechanical properties of materials and their changes with thermal treatments and/or mechanical treatments are essential to obtain the best results during simulation of processes. In this paper, changes of Young's modulus at room temperature of colddeformed aluminum AA1050 carried out in a tension machine and changes of Young’s modulus and Poisson’s ratio of AA2024 (T6 and T65) have been determined. The elastics constants have been measured by the ultrasound technique in AA2024 alloy and by tensile test in AA1050. In this alloy, the Young's modulus (E) diminishes during the first step of deformation and then increases with the successive cold working. Changes in Young's modulus measured are around 6-8%. In AA2024, the Young's modulus change is about 3% between the annealed and quenched alloy (minimum value); during aging the E parameter increases with respect to quenching. These changes are correlated with the structural changes during thermal treatments. In AA2024, the E parameter remains almost constant during cold-working after the aging treatment. Poisson’s ratio of this alloy remains almost constant in all the treatments. These results are also correlated with the dislocations arrangement in both materials. This behaviour is also compared with cold-deformed pure iron in a tensile test. These results confirm that aluminum AA1050 present similar behaviour than it was observed for pure iron.

Abstract: This research work analyses the effect of cold working level produced by drawing, on the work hardening exponent of 0.18 and 0.43 % C ferrite-pearlite steels. Such analysis is carried out by means of true stress-true strain curves derived from uniaxial tension tests. The work hardening exponent behaviour was determined by using Hollomon and differential Crussard-Jaoul models. It is found that the work hardening exponent decreases as a function of the applied cold-drawing level, and negative values were obtained when differential analysis is used. The results indicate that the Hollomon analysis shows some deviations from the experimentally determined true stress - true strain curves while the differential Crussard-Jaoul analysis fits better when two work hardening exponents are considered. This analysis establishes two exponents for different stages of plastic deformation which are determined by the sharp slope change in the plot of ln (d σ/d ε) - ln ε.