Omid Khalaj

Microstructure Evaluation of New ODS Alloys with Fe-Al Matrix and Al2O3 Particles

ODS steels are used for their very good mechanical properties at high temperature and low-cost production in comparison with other super alloys (ex. nickel super alloys). The paper describes a new group of Fe-Al Oxide Dispersion Strengthened (ODS) alloys with fine Al2O3 precipitates. ODS ferritic steels are high temperature creep resistant materials, which are intended to be applied more in the future industry. The steel was prepared by powder metallurgy under mechanical alloying and hot consolidation. To describe the stability of this material, annealing with different temperatures and holding times were carried out. The results show that the fine-grained microstructure is stable during long-term annealing up to 800 °C. At temperatures over 1000 °C, the grain structure coarsens by abnormal grain growth by keeping the size of oxides unchanged. Besides, the grain structure of the material is improved by differing the annealing time and temperature. The obtained structures were analyzed by optical and scanning electron microscopy. The mechanical properties and hardness were measured by tensile test at different temperatures.

Laboratory Investigation of Buried Pipes Using Geogrid and EPS Geofoam Block

This paper describes the results of laboratory tests conducted on flexible PVC pipes with diameter of 160 mm, buried in unreinforced and reinforced trench with geogrid layer and expanded polystyrene (EPS) geofoam block. The repeated load with amplitude of 450 kPa and frequency of 0.33 Hz was applied on the trench surface, using plate loading at a diameter of 150 mm to simulate the vehicle loads. Vertical diameter strain (VDS), strain at pipes crown and transferred pressure on the pipes crown were recorded throughout the test for up to 500 cycles of loading. The variables examined in the testing program include thickness of EPS block (30, 60 and 100 mm) and its density (10, 20 and 30 kg/cm3). The pipes were embedded at depths 1.5 times their diameter and the width of EPS block was kept constant at 2.0 times the pipe diameter in all tests. The results show that the values of VDS and pipe strain increased rapidly during the initial loading cycles, thereafter the rate of deformation and strain reduced significantly as the number of load cycles increased. According to the results, the minimum VDS and pipes crown strain were provided by 100 mm thickness and 30 kg/cm3 of EPS block placed over the pipe with a geogrid layer giving values of, respectively, 0.15 and 0.10 times those obtained in the reinforced trench with a geogrid layer.

Cyclic Response of Footing with Embedment Depth on Multi-Layered Geocell-Reinforced Bed

In order to investigate the effect of embedment depth on settlement of footing supported by geocell-reinforced bed, a series of cyclic plate loading at a diameter of 300 mm supported by layers of geocell in a test pit of 2000*2000 mm in plane and 700 mm in depth, were performed. The results show that installation of the geocell layers in the foundation bed toward embedded footing supported by one layer geocell has more effect on increasing the resilient behaviour in addition to reduction of accumulated plastic and total settlement of system. The study also compares the embedment depth ratio of one layer geocell reinforcement with two and three layer geocell reinforcement bed with no embedment depth.