Nur Iskandar Taib

Provenance and tectonic setting of Miocene siliciclastic sediments, Sibuti formation, northwestern Borneo

Provenance and tectonic setting of sandstone and mudstone units of the Miocene Sibuti Formation from northwest Borneo have been studied based on the mineralogy, major and trace element geochemistry data. The X-ray diffraction (XRD) and scanning electron microscopy-energy dispersive spectrometry (SEM-EDS) data revealed that the sandstones and mudstones were abundant in quartz, pyrite, clay, and heavy minerals such as zircon, rutile, and some detrital cassiterite. Geochemically, the sandstones and mudstones are classified into quartz arenite, litharenite, sublitharenite, arkose, and wacke. Quartz arenites are enriched with SiO2, Zr, and Th and depleted in Al2O3, CaO, and other elements compared to other sandstone types, indicating high maturity and intensive weathering. Chemical index of alteration (CIA: 77–90), plagioclase index of alteration (PIA: 86–100), and A-CN-K diagram suggest intense weathering in the source area. Elemental ratios such as La/Sc, Th/Sc, Cr/Th, La/Co, and Th/Co are similar to sediments derived from the felsic rocks. Also, the provenance discrimination diagrams suggest recycled continental nature of these clastic sediments which are mostly derived from metasedimentary source (Rajang Formation). Discriminant-function diagram for the tectonic discrimination of siliciclastic sediments revealed that the sediments of Sibuti Formation were derived from a collision zone, which is consistent with the geology of the study area.

ASSESSMENT OF ABORIGINAL SMALLHOLDER SOILS FOR RUBBER GROWTH IN PENINSULAR MALAYSIA

This study assesses an array of physiochemical soil properties from a sample of rubber smallholdings managed by a group of Orang Asli(original people) in northwest Pahang, Peninsular Malaysia. Malaysian smallholders in general face significantly lower productivity levels than the large rubber estates and plantations (Malaysian Rubber Board, 2002). Among smallholders, Orang Asli households generate the lowest rubber yields, earn the lowest non-rubber income, and are most threatened by land scarcity (RISDA, 2003). Furthermore, little is known about the soils of these smallholdings since most rubber-related soil surveys focus on estates and experiment stations (Pushparajah & Amin, 1977). An understanding of the morphological and physiochemical soil properties of Orang Asli rubber fields is a crucial step toward the efficient allocation of government resources that aim to enhance productivity, promote sustainable agriculture, and improve household welfare. The objectives of this project were to (1) determine the predominant physiochemical characteristics of these soils, (2) evaluate them with an established rubber suitability classification system, (3) group soils according to region, geomorphic position, and estimated soil series in order to make generalizations about soil limitations for certain soil types, and (4) offer methods by which to mitigate the effects of these limitations. We find that there is a great deal of heterogeneity within our sample with regard to both soil type and limitation. The most common physical limitations were related to flooding, uprooting, soil texture, and slope. Almost all soils were severely depleted in organic nutrients and base cations. Overall, these limitations were correctable via drainage, terracing, or establishment of a cover crop. It is recommended that any application of chemical fertilizer take soil type into account. (Soil Science 2005;170:1034-1049)

Failure of car’s drive shaft under torsion

Abstract This investigation reports analysis of fracture by splitting a car’s front wheel drive shaft into two parts, which ruptured at a very early stage (<10 cycles) of its endurance/driving test. Besides computations for shear stress and shear strength, a number of experimental techniques, e.g. non-destructive testing (ultrasonic flaw detection), chemical and metallographic analyses, hardness measurements, scanning electron microscopy (SEM) and electron probe microanalysis (EPMA) techniques, are used to determine the cause of the drive shaft’s fracture. Non-destructive testing results showed the absence of any internal crack or flaw in the failed component, thereby excluding possibility of fast fracture due to propagation of crack. Scanning electron microscopy fractographs showed cleavage fracture at the outer surface of the shaft, whereas chemical analysis results showed that the steel used in the drive shaft conforms to mild steel. On the basis of the design calculations, it is concluded that failure of the shaft occurs due to shear overstressing. On the basis of hardness profile, it is concluded that the shaft has been casehardened by induction hardening. It is recommended that the steel of 25CrMo4/27CD4 type should be selected in the manufacturing of drive shaft, which should be casehardened by carbonitriding for application in modern cars.