Page 303 - 00. Complete Version - Progress Report IPEN 2014-2016

Materials and Nanotechnology | Progress Report 303

Mechanical Properties DSA in the (b) and (c) conditions.

Fracture mechanics and A fracture mechanics analysis of flaws in grind-
mechanical properties of metals, ing balls mills for mining plants was under-
alloys and composites taken and the theoretical values of growth

rate of those defects were compared with ac-
An elastic-plastic fracture mechanics study of tual values obtained through periodic inspec-
the application of Leak-Before-Break (LBB) con- tions performed in this component. The cracks
cept in a relatively small-diameter (273 mm nucleation was caused by lack of lubrication
diameter) high-energy nuclear reactor cool- in the trunnion bearings, generating circum-
ant line was done, where it is proposed AISI ferential thermal stresses and the estimated
316LN type stainless steel to be used as base temperature of the trunnion and bushing con-
material welded with AISI 316L coated elec- tact reached 150°C. During the analyzed peri-
trode. Results show a well-defined mechani- od, the results obtained by the BS7910 stan-
cal behavior where base material has a high dard proved to be closer to the actual values
toughness, weld region has a low toughness, than the ASME Section XI standard.
and HAZ shows intermediate properties. For
the load limit analysis, the lowest critical crack A study of the influence of solution heat treat-
size was found for base material presenting ment temperature on the hardness response in
circumferential cracks. For J-integral analysis, incoloy 945 was done. Incoloy 945 is a hybrid
it was demonstrated that tearing instability Ni-Fe-Cr based superalloy with a mechanical
leading to failure would not occur. strength and corrosion resistance comparable
to those of Inconel 718 and Incoloy 925, respec-
A preliminary draft version of a surveillance tively, with minimum yield strength reaching
program for the materials presented in the nu- 860 MPa. The heat treatment at 1000°C caus-
cleus of Brazilian Multipurpose Reactor (RMB) es a hardness reduction around 61%, reaching
was developed. The surveillance program is 63% at the temperature of 1020°C. The reasons
needed to confirm and determine the effects for the reductions are the dissolution of the
of radiation on the mechanical properties of gamma prime hardening phase and a slight
the core reactor materials: its effects on the grain growth (ASTM 7). Above this tempera-
tensile properties (strength and ductility), frac- ture, the hardness loss is negligible, however,
ture toughness, radiation-induced growth and grain growth is more pronounced reaching
corrosion. a ASTM 2 grain size in the specimens treat-
ed at 1050°C.
The mechanical behavior of high strength alu-
minum alloys of the 7075 series is under inves- Aluminum alloys for
tigation, to study the occurrence of dynamic automotive applications
strain aging (DSA: Portevin-Le Chatellier effect)
on tensile specimens, submitted to different Automobile parts made of steel/cast iron have
heat-treatment conditions: (a) solution heat been replaced with those made with alumi-
treated then artificially aged, T6, (b) T6 then num alloys to not only reduce weight, but also
solution heat treated at 485°C for 5 hours, (c) to reduce fuel consumption the emission of
T6 then solution heat treated at 300°C for 5 h. pollutants. Structural materials require not
Preliminary results show the occurrence of only high strength/weight ratio, besides rea-