TEMPERATURE AND STRAIN-RATE DEPENDENCE OF FRACTURE-TOUGHNESS OF PHENOLPHTHALEIN POLYETHER KETONE

A strong strain-rate and temperature dependence was observed for the fracture toughness of phenolphthalein polyether ketone (PEK-C). Two separate crack-blunting mechanisms have been proposed to account for the fracture-toughness data. The first mechanism involves thermal blunting due to adiabatic heating at the crack tip for the high temperatures studied. In the high-temperature range, thermal blunting increases the fracture toughness corresponding to an effectively higher test temperature. However, in the low-temperature range, the adiabatic temperature rise is insufficient to cause softening and Jic increases with increasing temperature owing to viscoelastic losses associated with the p-relaxation there. The second mechanism involves plastic blunting due to shear yield/flow processes at the crack tip and this takes place at slow strain testing of the single-edge notched bending (SENB) samples. The temperature and strain-rate dependence of the plastic zone size may also be responsible for the temperature and strain-rate dependence of fracture toughness.

Geophysical evaluation methods for buried hill reservoirs in the Jiyang superdepression of the Bohai Bay basin, eastern China

The Jiyang superdepression is one of the richest hydrocarbon accumulations in the Bohai Bay basin, eastern China. Comprehensive seismic methods have been used in buried hill exploration in Jiyang to describe these fractured reservoirs better. Accurate seismic stratigraphic demarcation and variable-velocity mapping were applied to reveal the inner structure of the buried hills and determine the nature of the structural traps more precisely. Based on the analysis of rock properties and the characteristics of well-developed buried hill reservoirs, we have successfully linked the geology and seismic response by applying seismic forward technology. Log-constrained inversion, absorption coefficient analysis and tectonic forward-inversion with FMI loggings were applied to analyse and evaluate the buried hill reservoirs and gave satisfying results. The reservoir prediction was successful, which confirmed that the comprehensive utilization of these methods can be helpful in the exploration of buried hill reservoirs.

高邮凹陷陈堡及陈堡东地区油气成藏规律研究

With the development of petroleum exploration in Gaoyou Depression, both old and new areas have been the active exploration targets, so the study of petroleum accumulation is significant to the petroleum exploration in the study area and the integrated oil and gas accumulation theory. Based on hydrocarbon accumulation theory and systematical research methods and combined with the structural characteristics of Gaoyou Depression, Chenbao and East of Chenbao were selected as the study areas in this dissertation, oil and gas migration pathways, accumulation periods, as well as accumulation models were studied, and favorable exploration targets were proposed. There develop three sets source rocks, which are Tai-2 Member, Fu-2 Member and Fu-4 Member respectively. Tai-2 Member is the predominant source rock in the eastern part. Fu-2 Member mainly occurs in the northern slope, while Fu-4 Member develops in the deep depression. In the study area, oil mainly comes from Fu-2 Member of Liuwushe subsag. The lower limit of TOC is 0.4%, and active source rock mostly distributed in the south fault-step zone. The source rock in Liuwushe subsag began to generate hydrocarbon in the late of Dainan depositional stage and the threshold was 2300m. The macro and micro characteristics of reservoirs and the reservoir heterogeneity characteristics of the Fu-1 Member were studied systematicly. The results show that Fu-1 Member, which has better reservoir properties, are medium porosity-medium permeability reservoir. The reservoir permeability has good correlation with porosity connectivity. The reservoirs have strong dissolution, pores are mainly thin to medium throat, and throat radii are distributed concentratedly, the sorting is good and pore structures are homogeneous. Sandstone reservoirs whether in the plan view, interlayer or in layers have a certain degree of heterogeneity, in particular, the heterogeneity in layers directly affect and control the oil and gas migration and accumulation. By analyzing the lithology correlation of the fault walls, shale smear, cross section stress, the configuration of fracture active periods and hydrocarbon generation and expulsion periods and fuzzy comprehensive evaluation, the main faults sealing were evaluated. The results show that the faults in Chenbao and East of Chenbao had poor sealing properties in Sanduo period and could be used as the migration pathways at that time. After Sanduo period, the tectonic stress fields in the area changed largely, and, consequently, the fault properties converted from tensional shear to compressive shear, the faults changed progressively from close to open, so the faults sealing became better and were conducive to the preservation of oil and gas reservoirs. According to the seismic event suspension modes and profile configurations above and under the unconformities, combined with tectonic evolutions of the study areas, the unconformity types can be classified into truncation unconformity, overlapped unconformity and parallel unconformity and the distribution characteristics of unconformities in the plan view was also studied. The unconformity structure was divided into basal conglomerate, weathered clay and semi-weathered layer vertically in the study area and this kind of structure make unconformities to be effective oil and gas migration pathways and is significant to hydrocarbon accumulation in a parts of areas. With the analyses of typical oil and gas reservoirs in the study area, combined with the research results of pathway systems, hydrocarbon accumulation models were established and the oil and gas accumulation laws in Chenbao and East of Chenbao analyzed. The oil and gas came from Liuwushe subsag and Liuliushe subsag. The oil and gas from Liuwushe subsag mainly migrated from the structural high parts into the fault-step zone along strata in northeast direction, a part of them migrated upward into the fault-step zone and the Wubao low uplift along Wu-1 Fault in northeast direction. The oil and gas from Liuliushe subsag mainly migrated into the upper reservoirs through Wu-2 fault, and lesser oil and gas migrated into the fault-step zone because of the controls of cross-section orientation, depression center and the hydrocarbon formation tendency. The favorable exploration targets in Chenbao and East of Chenbao have been concluded: the southern fault-step zone is a favorable oil and gas accumulation zone of Liuwushe subsag, and they are fault block reservoirs where fault acted as the barriers, the main target intervals are Fu-1 Member and Fu-3 Member in palaeocene; Oil and gas in the middle and northern fault-step zone mainly laterally migrated from the south areas, and the main target interval is Fu-3 Member in palaeocene; Fu-1 Member and the reserviors above the Wubao subsag are still the focuses in future explorations. The results of this study have important guiding significance for the future oil and gas exploration.

Large bio-geographical shifts in the north-eastern Atlantic Ocean: From the subpolar gyre, via plankton, to blue whiting and pilot whales

Pronounced changes in fauna, extending from the English Channel in the south to the Barents Sea in the north-east and off Greenland in the north-west, have occurred in the late 1920s, the late 1960s and again in the late 1990s. We attribute these events to exchanges of subarctic and subtropical water masses in the north-eastern North Atlantic Ocean, associated with changes in the strength and extent of the subpolar gyre. These exchanges lead to variations in the influence exerted by the subarctic or Lusitanian biomes on the intermediate faunistic zone in the north-eastern Atlantic. This strong and persistent bottom-up bio-physical link is demonstrated using a numerical ocean general circulation model and data on four trophically connected levels in the food chain – phytoplankton, zooplankton, blue whiting, and pilot whales. The plankton data give a unique basin-scale depiction of these changes, and a long pilot whale record from the Faroe Islands offers an exceptional temporal perspective over three centuries. Recent advances in simulating the dynamics of the subpolar gyre suggests a potential for predicting the distribution of the main faunistic zones in the north-eastern Atlantic a few years into the future, which might facilitate a more rational management of the commercially important fisheries in this region.

Contact zone dynamics and the evolution of reproductive isolation in a North American treefrog, the spring peeper (Pseudacris crucifer)

Despite over seven decades of speciation research and 25 years of phylogeographic studies, a comprehensive understanding of mechanisms that generate biological species remains elusive. In temperate zones, the pervasiveness of range fragmentation and subsequent range expansions suggests that secondary contact between diverging lineages may be important in the evolution of species. Thus, such contact zones provide compelling opportunities to investigate evolutionary processes, particularly the roles of geographical isolation in initiating, and indirect selection against hybrids in completing (reinforcement), the evolution of reproductive isolation and speciation. The spring peeper (Pseudacris crucifer) has six well-supported mitochondrial lineages many of which are now in secondary contact. Here I investigate the evolutionary consequences of secondary contact of two such lineages (Eastern and Interior) in Southwestern Ontario using genetic, morphological, acoustical, experimental, and behavioural evidence to show accentuated divergence of the mate recognition system in sympatry. Mitochondrial and microsatellite data distinguish these two lineages but also show ongoing hybridization. Bayesian assignment tests and cline analysis imply asymmetrical introgression of Eastern lineage nuclear markers into Interior populations. Male calls are divergent between Eastern and Interior allopatric populations and show asymmetrical reproductive character displacement in sympatry. Female preference of pure lineage individuals is also exaggerated in sympatry, with hybrids showing intermediate traits and preference. I suggest that these patterns are most consistent with secondary reinforcement. I assessed levels of post-zygotic isolation between the Eastern and Interior lineages using a laboratory hybridization experiment. Hybrid tadpoles showed equal to or greater fitness than their pure lineage counterparts, but this may be countered through competition. More deformities and developmental anomalies in hybrid tadpoles further suggest post-zygotic isolation. Despite evidence for pre-mating isolation between the two lineages, isolation appears incomplete (i.e. hybridization is ongoing). I hypothesize that potentially less attractive hybrids may circumvent female choice by adopting satellite behaviour. Although mating tactics are related to body size, genetic status may play a role. I show that pure Eastern males almost always engage in calling, while hybrids adopt a satellite tactic. An absence of assortative mating, despite evidence of female preference, suggests successful satellite interception possibly facilitating introgression.

Multi-scale dynamics on the Eastern Brazilian margin

Este trabalho combina esforços de simulação numérica e de análise de dados para investigar a dinâmica em diversos compartimentos (oceano aberto, plataforma continental e zona costeira-estuarina) e, em multiplas escalas, na Margem Continental Leste Brasileira (MCLB). A circulação de largo e mesoescala espacial e a propagação da maré barotrópica são investigadas através de uma configuração aninhada do modelo numérico ROMS. O estudo da dinâmica regional da Baía de Camamu (CMB) baseia-se na análise de dados locais. A MCLB, localizada a SW do Atlântico Sul entre 8±S e 20±S, possui plataforma estreita, batimetria complexa, e baixa produtividade primária. A sua dinâmica é influenciada pela divergência da Corrente Sul Equatorial (CSE). As simulações refletem as conexões sazonais e espaciais entre a Corrente do Brasil e a Contra Corrente Norte do Brasil , em conexão com a dinâmica da CSE. As simulações revelam atividades vorticais nas proximidades da costa e interações com a dinâmica costeira, cujos padrões são descritos. A validação do modelo em mesoescala é baseada em cálculos de energia cinética turbulenta e em dados históricos de transporte. A CMB, localizada a 13±400S, abriga uma comunidade piscatória tradicional e extenso de manguezal. Situa-se porém sobre uma bacia sedimentar com grande reservas de óleo e gás, estando em tensão permanente de impacto ambiental. Neste trabalho sumarizamos as condições físicas regionais e investigamos sua dinâmica interna, focando sua variabilidade em amostragens realizadas sob condições de seca (Setembro de 2004) e de chuva (Julho de 2005). Finalmente, o modelo numérico ROMS é forçado com o sinal de maré, empregando-se uma configuração simples (com coeficientes de atrito de fundo constantes e condições hidrográficas homogéneas), com o intuito de avaliar sua resposta e investigar a natureza da propagação da maré barotrópica na MCLB, convergindo na CMB. A análise da resposta do modelo à maré basea-se em séries históricas do nível do mar para a MCLB e dados recentes da CMB.

Modelling adhesive joints with cohesive zone models: effect of the cohesive law shape of the adhesive layer

Adhesively-bonded joints are extensively used in several fields of engineering. Cohesive Zone Models (CZM) have been used for the strength prediction of adhesive joints, as an add-in to Finite Element (FE) analyses that allows simulation of damage growth, by consideration of energetic principles. A useful feature of CZM is that different shapes can be developed for the cohesive laws, depending on the nature of the material or interface to be simulated, allowing an accurate strength prediction. This work studies the influence of the CZM shape (triangular, exponential or trapezoidal) used to model a thin adhesive layer in single-lap adhesive joints, for an estimation of its influence on the strength prediction under different material conditions. By performing this study, guidelines are provided on the possibility to use a CZM shape that may not be the most suited for a particular adhesive, but that may be more straightforward to use/implement and have less convergence problems (e.g. triangular shaped CZM), thus attaining the solution faster. The overall results showed that joints bonded with ductile adhesives are highly influenced by the CZM shape, and that the trapezoidal shape fits best the experimental data. Moreover, the smaller is the overlap length (LO), the greater is the influence of the CZM shape. On the other hand, the influence of the CZM shape can be neglected when using brittle adhesives, without compromising too much the accuracy of the strength predictions.

Evolução cenozóica da área de Longroiva-Vilariça (NE Portugal)

In the Longroiva-Vilariça area, the identification of Cenozoic lithostratigraphic units, the sedimentology and the characterization of its geometric relations with tectonic structures allowed the interpretation of the palaeogeographic main stages: 1) the greenwhitish Vilariça Arkoses (Middle Eocene to Oligocene ?) represent proximal sediments of a very low gradient drainage towards the eastern Spanish Tertiary Duero Basin; 2)Quintãs Formation (late Miocene ?) are brown-reddish coloured piedmont alluvial deposits, correlative of important vertical displacement (western tectonic block relative uplift) along the NNE-SSW indent-linked strike-slip Bragança-Vilariça-Longroiva fault zone, interpreted as a reactivated deep hercynian fracture, with left-lateral movement; 3) the red Sampaio Formation (Gelasian-early Pleistocene ?)was interpreted as downhill conglomeratic deposits related with important overtrusting along this fault zone (the definition of the present-day narrow graben configuration) and correlative of the atlantic hydrographic incision stage beginning; 4) conglomeratic terraces (middle and late Pleistocene ?); 5) alluvial plains and colluvial deposits (Holocene).

The role of a transcrustal shear zone in orogenic gold mineralization at the Aijanahalli Mine, Dharwar Craton, South India

The Ajjanahalli gold mine is spatially associated with a Late Archean craton-scale shear zone in the eastern Chitradurga greenstone belt of the Dharwar craton, India. Gold mineralization is hosted by an similar to100-m-wide antiform in a banded iron formation. Original magnetite and siderite are replaced by a peak metamorphic alteration assemblage of chlorite, stilpnomelane, minnesotaite, sericite, ankerite, arsenopyrite, pyrite, pyrrhotite, and gold at ca. 300degrees to 350degreesC. Elements enriched in the banded iron formation include Ca, Mg, C, S, An, As, Bi. Cu, Sb, Zn, Pb, Se, Ag, and Te, whereas in the wall rocks As, Cu, Zn, Bi, Ag, and An are only slightly enriched. Strontium correlates with CaO, MgO, CO2, and As, which indicates cogenetic formation of arsenopyrite and Mg-Ca carbonates. The greater extent of alteration in the Fe-rich banded iron formation layers than in the wall rock reflects the greater reactivity of the banded iron formation layers. The ore fluids, as interpreted from their isotopic composition (delta(18)O = 6.5-8.5parts per thousand; initial Sr-87/Sr-86 = 0.7068-0.7078), formed by metamorphic devolatilization of deeper levels of the Chitradurga greenstone belt. Arsenopyrite, chalcopyrite, and pyrrhotite have delta(34)S values within a narrow range between 2.1 and 2.7 per mil, consistent with a sulfur source in Chitradurga greenstone belt lithologies. Based on spatial and temporal relationships between mineralization, local structure development, and sinistral strike-slip deformation in the shear zone at the eastern contact of the Chitradurga greenstone belt, we suggest that the Ajjanahalli gold mineralization formed by fluid infiltration into a low strain area within the first-order structure. The ore fluids were transported along this shear zone into relatively shallow crustal levels during lateral terrane accretion and a change from thrust to transcurrent tectonics. Based on this model of fluid flow, exploration should focus on similar low strain areas or potentially connected higher order splays of the first-order shear zone.

Microphytoplankton community structure in the North Eastern Arabian Sea during Winter Monsoon

The overall attempt of the study was aimed to understand the microphytoplankton community composition and its variations along a highly complex and dynamic marine ecosystem, the northern Arabian Sea. The data generated provides a first of its kind knowledge on the major primary producers of the region. There appears significant response among the microphytoplankton community structure towards the variations in the hydrographic conditions during the winter monsoon period. Interannually, variations were observed within the microphytoplankton community associated with the variability in temperature patterns and the intensity of convective mixing. Changing bloom pattern and dominating species among the phytoplankton community open new frontiers and vistas towards more intense study on the biological responses towards physical processes. The production of large amount of organic matter as a result of intense blooming of Noctiluca as well as diatoms aggregations augment the particulate organic substances in these ecosystem. This definitely influences the carbon dynamics of the northern Arabian Sea. Detailed investigations based on time series as well as trophodynamic studies are necessary to elucidate the carbon flux and associated impacts of winter-spring blooms in NEAS. Arabian sea is considered as one among the hotspot for carbon dynamics and the pioneering records on the major primary producers fuels carbon based export production studies and provides a platform for future research. Moreover upcoming researches based on satellite based remote sensing on productivity patterns utilizes these insitu observations and taxonomic data sets of phytoplankton for validation of bloom specific algorithm development and its implementation. Furthermore Saurashtra coast is considered as a major fishing zone of Indian EEZ. The studies on the phytoplankton in these regions provide valuable raw data for fishery prediction models and identifying fishing zones. With the Summary and Conclusion 177 baseline data obtained further trophodynamic studies can be initiated in the complex productive North Eastern Arabian Seas (NEAS) ecosystem that is still remaining unexplored.

The prediction of seasonal and inter-annual climate variations and their impacts on the water resources in the eastern seaboard of Thailand

The research of this thesis dissertation covers developments and applications of short-and long-term climate predictions. The short-term prediction emphasizes monthly and seasonal climate, i.e. forecasting from up to the next month over a season to up to a year or so. The long-term predictions pertain to the analysis of inter-annual- and decadal climate variations over the whole 21st century. These two climate prediction methods are validated and applied in the study area, namely, Khlong Yai (KY) water basin located in the eastern seaboard of Thailand which is a major industrial zone of the country and which has been suffering from severe drought and water shortage in recent years. Since water resources are essential for the further industrial development in this region, a thorough analysis of the potential climate change with its subsequent impact on the water supply in the area is at the heart of this thesis research. The short-term forecast of the next-season climate, such as temperatures and rainfall, offers a potential general guideline for water management and reservoir operation. To that avail, statistical models based on autoregressive techniques, i.e., AR-, ARIMA- and ARIMAex-, which includes additional external regressors, and multiple linear regression- (MLR) models, are developed and applied in the study region. Teleconnections between ocean states and the local climate are investigated and used as extra external predictors in the ARIMAex- and the MLR-model and shown to enhance the accuracy of the short-term predictions significantly. However, as the ocean state – local climate teleconnective relationships provide only a one- to four-month ahead lead time, the ocean state indices can support only a one-season-ahead forecast. Hence, GCM- climate predictors are also suggested as an additional predictor-set for a more reliable and somewhat longer short-term forecast. For the preparation of “pre-warning” information for up-coming possible future climate change with potential adverse hydrological impacts in the study region, the long-term climate prediction methodology is applied. The latter is based on the downscaling of climate predictions from several single- and multi-domain GCMs, using the two well-known downscaling methods SDSM and LARS-WG and a newly developed MLR-downscaling technique that allows the incorporation of a multitude of monthly or daily climate predictors from one- or several (multi-domain) parent GCMs. The numerous downscaling experiments indicate that the MLR- method is more accurate than SDSM and LARS-WG in predicting the recent past 20th-century (1971-2000) long-term monthly climate in the region. The MLR-model is, consequently, then employed to downscale 21st-century GCM- climate predictions under SRES-scenarios A1B, A2 and B1. However, since the hydrological watershed model requires daily-scale climate input data, a new stochastic daily climate generator is developed to rescale monthly observed or predicted climate series to daily series, while adhering to the statistical and geospatial distributional attributes of observed (past) daily climate series in the calibration phase. Employing this daily climate generator, 30 realizations of future daily climate series from downscaled monthly GCM-climate predictor sets are produced and used as input in the SWAT- distributed watershed model, to simulate future streamflow and other hydrological water budget components in the study region in a multi-realization manner. In addition to a general examination of the future changes of the hydrological regime in the KY-basin, potential future changes of the water budgets of three main reservoirs in the basin are analysed, as these are a major source of water supply in the study region. The results of the long-term 21st-century downscaled climate predictions provide evidence that, compared with the past 20th-reference period, the future climate in the study area will be more extreme, particularly, for SRES A1B. Thus, the temperatures will be higher and exhibit larger fluctuations. Although the future intensity of the rainfall is nearly constant, its spatial distribution across the region is partially changing. There is further evidence that the sequential rainfall occurrence will be decreased, so that short periods of high intensities will be followed by longer dry spells. This change in the sequential rainfall pattern will also lead to seasonal reductions of the streamflow and seasonal changes (decreases) of the water storage in the reservoirs. In any case, these predicted future climate changes with their hydrological impacts should encourage water planner and policy makers to develop adaptation strategies to properly handle the future water supply in this area, following the guidelines suggested in this study.

Catchment-scale modelling of flow and nutrient transport in the Chalk unsaturated zone

The unsaturated zone exerts a major control on the delivery of nutrients to Chalk streams, yet flow and transport processes in this complex, dual-porosity medium have remained controversial. A major challenge arises in characterising these processes, both at the detailed mechanistic level and at an appropriate level for inclusion within catchment-scale models for nutrient management. The lowland catchment research (LOCAR) programme in the UK has provided a unique set of comprehensively instrumented groundwater-dominated catchments. Of these, the Pang and Lambourn, tributaries of the Thames near Reading, have been a particular focus for research into subsurface processes and surface water-groundwater interactions. Data from LOCAR and other sources, along with a new dual permeability numerical model of the Chalk, have been used to explore the relative roles of matrix and fracture flow within the unsaturated zone and resolve conflicting hypotheses of response. From the improved understanding gained through these explorations, a parsimonious conceptualisation of the general response of flow and transport within the Chalk unsaturated zone was formulated. This paper summarises the modelling and data findings of these explorations, and describes the integration of the new simplified unsaturated zone representation with a catchment-scale model of nutrients (INCA), resulting in a new model for catchment-scale flow and transport within Chalk systems: INCA-Chalk. This model is applied to the Lambourn, and results, including hindcast and forecast simulations, are presented. These clearly illustrate the decadal time-scales that need to be considered in the context of nutrient management and the EU Water Framework Directive. (C) 2007 Elsevier B.V. All rights reserved.

Measuring toughness and the cohesive stress-displacement relationship by the essential work of fracture concept

The complete fracture behaviour of ductile double edge notched tension (DENT) specimen is analysed with an approximate model, which is then used to discuss the essential work of fracture (EWF) concept. The model results are compared with the experimental results for an aluminium alloy 6082-O. The restrictions on the ligament size for valid application of the EWF method are discussed with the aid of the model. The model is used to suggest an improved method of obtaining the cohesive stress-displacement relationship for the fracture process zone (FPZ).

Mode I fracture of sheet metal

The perceived wisdom about thin sheet fracture is that (i) the crack propagates under mixed mode I & III giving rise to a slant through-thickness fracture profile and (ii) the fracture toughness remains constant at low thickness and eventually decreases with increasing thickness. In the present study, fracture tests performed on thin DENT plates of various thicknesses made of stainless steel, mild steel, 6082-O and NS4 aluminium alloys, brass, bronze, lead, and zinc systematically exhibit (i) mode I “bath-tub”, i.e. “cup & cup”, fracture profiles with limited shear lips and significant localized necking (more than 50% thickness reduction), (ii) a fracture toughness that linearly increases with increasing thickness (in the range of 0.5–5 mm). The different contributions to the work expended during fracture of these materials are separated based on dimensional considerations. The paper emphasises the two parts of the work spent in the fracture process zone: the necking work and the “fracture” work. Experiments show that, as expected, the work of necking per unit area linearly increases with thickness. For a typical thickness of 1 mm, both fracture and necking contributions have the same order of magnitude in most of the metals investigated. A model is developed in order to independently evaluate the work of necking, which successfully predicts the experimental values. Furthermore, it enables the fracture energy to be derived from tests performed with only one specimen thickness. In a second modelling step, the work of fracture is computed using an enhanced void growth model valid in the quasi plane stress regime. The fracture energy varies linearly with the yield stress and void spacing and is a strong function of the hardening exponent and initial void volume fraction. The coupling of the two models allows the relative contributions of necking versus fracture to be quantified with respect to (i) the two length scales involved in this problem, i.e. the void spacing and the plate thickness, and (ii) the flow properties of the material. Each term can dominate depending on the properties of the material which explains the different behaviours reported in the literature about thin plate fracture toughness and its dependence with thickness.

Fracture and fatigue of natural fiber-reinforced cementitious composites

This paper presents the results of an experimental study of resistance-curve behavior and fatigue crack growth in cementitious matrices reinforced with eco-friendly natural fibers obtained from agricultural by-products. The composites include: blast furnace slag cement reinforced with pulped fibers of sisal, banana and bleached eucalyptus pulp, and ordinary Portland cement composites reinforced with bleached eucalyptus pulp. Fracture resistance (R-curve) and fatigue crack growth behavior were studied using single-edge notched bend specimens. The observed stable crack growth behavior was then related to crack/microstructure interactions that were elucidated via scanning electron microscopy (SEM) and energy dispersive X-ray spectroscopy (EDS). Fracture mechanics models were used to quantify the observed crack-tip shielding due to crack-bridging. The implications of the results are also discussed for the design of natural fiber-reinforced composite materials for affordable housing. (C) 2009 Elsevier Ltd. All rights reserved.