Intact Material Research Articles

Use of Pulsating Water Jet Technology for Removal of Concrete in Repair of Concrete Structures

High-speed water jet technology is commonly used for removing degraded concrete surface layers selectively in the process of repair of concrete structures. This technology offers number of advantages (such as reduced noise, dust and vibrations, preservation of intact material and thus more delicate intervention into the structure), but it still requires further improvement in terms of productivity and cost effectiveness to be even more competitive to traditional methods of concrete surface layers removal. The impact of a high-velocity liquid drop or bunch of water on a rigid surface generates extremely short high-pressure transients that can cause substantially serious damage to the surface and interior of the solid material. Therefore, the use of pulsating water jets, that are able to generate repeatedly above mentioned high-pressure transients, can lead to higher performance of pulsating high-speed water jets compared to continuous ones under the same operating conditions. A special method of the generation of the high-speed pulsating water jet was developed recently and tested extensively under laboratory conditions. The method is based on the generation of acoustic waves by the action of the acoustic transducer on the pressure liquid and their transmission via pressure system to the nozzle. A series of laboratory experiments was performed to compare effects of pulsating and continuous jets (both rotating and flat fan) acting on concrete surface. A rate of concrete removal was used to evaluate the jet. Results of the study of effects of pulsating and continuous high-speed water jets on concrete surfaces using methods of optical microscopy and image analysis are also discussed in this paper.

Probabilistic analysis and design of strip foundations resting on rocks obeying Hoek–Brown failure criterion

In this paper, a probabilistic analysis is presented to compute the probability density function (PDF) of the ultimate bearing capacity of a shallow strip footing resting on a rock mass. The rock is assumed to follow the modified Hoek–Brown failure criterion. Vertical and inclined loading cases are considered in the analysis. In this study, the deterministic models are based on the kinematic approach of the limit analysis theory. The polynomial chaos expansion (PCE) methodology is used for the probabilistic analysis. Four parameters related to the modified Hoek–Brown failure criterion are considered as random variables. These are the geological strength index ( GSI), the uniaxial compressive strength of the intact rock ( σ c ), the intact rock material constant ( m i ) and the disturbance coefficient ( D). The results of the vertical load case have shown that (i) the variability of the ultimate bearing capacity increases with the increase in the coefficients of variation of the random variables; GSI and σ c being of greater effect, (ii) the non-normality of the input variables has a significant effect on the shape of the PDF of the ultimate bearing capacity, (iii) a negative correlation between GSI and σ c leads to less spread out PDF, (iv) the probabilistic footing breadth based on a reliability-based design (RBD) may be greater or smaller than the deterministic breadth depending on the values of the input statistical parameters. Finally, it was shown in the inclined load case that the variability of the ultimate bearing capacity decreases with the increase of the footing load inclination.

The Effect of Boundary Condition on the Biomechanics of a Human Pelvic Joint Under an Axial Compressive Load: A Three-Dimensional Finite Element Model

The finite element (FE) model of the pelvic joint is helpful for clinical diagnosis and treatment of pelvic injuries. However, the effect of an FE model boundary condition on the biomechanical behavior of a pelvic joint has not been well studied. The objective of this study was to study the effect of boundary condition on the pelvic biomechanics predictions. A 3D FE model of a pelvis using subject-specific estimates of intact bone structures, main ligaments and bone material anisotropy by computed tomography (CT) gray value was developed and validated by bone surface strains obtained from rosette strain gauges in an in vitro pelvic experiment. Then three FE pelvic models were constructed to analyze the effect of boundary condition, corresponding to an intact pelvic joint, a pelvic joint without sacroiliac ligaments and a pelvic joint without proximal femurs, respectively. Vertical load was applied to the same pelvis with a fixed prosthetic femoral stem and the same load was simulated in the FE model. A strong correlation coefficient (R(2)=0.9657) was calculated, which indicated a strong correlation between the FE analysis and experimental results. The effect of boundary condition changes on the biomechanical response depended on the anatomical location and structure of the pelvic joint. It was found that acetabulum fixed in all directions with the femur removed can increase the stress distribution on the acetabular inner plate (approximately double the original values) and decrease that on the superior of pubis (from 7 MPa to 0.6 MPa). Taking sacrum and ilium as a whole, instead of sacroiliac and iliolumber ligaments, can influence the stress distribution on ilium and pubis bone vastly. These findings suggest pelvic biomechanics is very dependent on the boundary condition in the FE model.

Leaf Spray: Direct Chemical Analysis of Plant Material and Living Plants by Mass Spectrometry

The chemical constituents of intact plant material, including living plants, are examined by a simple spray method that provides real-time information on sugars, amino acids, fatty acids, lipids, and alkaloids. The experiment is applicable to various plant parts and is demonstrated for a wide variety of species. An electrical potential is applied to the plant and its natural sap, or an applied solvent generates an electrospray that carries endogenous chemicals into an adjacent benchtop or miniature mass spectrometer. The sharp tip needed to create a high electric field can be either natural (e.g., bean sprout) or a small nick can be cut in a leaf, fruit, bark, etc. Stress-induced changes in glucosinolates can be followed on the minute time scale in several plants, including potted vegetables. Differences in spatial distributions and the possibility of studying plant metabolism are demonstrated.

Skeleton Pattern and Joint Formation in Chorioallantoic Grafts Containing the Distal Parts of the Chick Wing Bud

Skeleton pattern formation was examined in chick wing bud grafts using the chorioallantoic grafting method. The distal parts of the wing bud were excised from the donor wing and transplanted onto the chorioallantoic membrane (the experimental groups). Transplants with intact limb bud material served as the control group. The skeleton pattern formation in the grafts depended on the amount of transplanted material and donor's limb bud stage. The younger the donor's stage and the bigger the piece of the transplanted material the more proximal parts grafts had, more retarded growth and abnormal skeleton in the zeugopod and autopod was. The percentage of the signs of insufficient blood supply in the experimental groups was less than that in the control group. As the amount of the transplanted limb bud material decreased and donor's limb bud aged, post-axial polydactyly changed to the pre-axial one.

Use of Digital Terrestrial Photogrammetry in rocky slope stability analysis by Distinct Elements Numerical Methods

Current approaches to rocky slope stability analysis require knowledge of the geometrical–structural setting, as well as the physical–mechanical properties of the intact material and its discontinuities. The physical–mechanical properties are derived from in situ and laboratory tests, whereas the geometrical characteristics come from field attitude measurements. Frequently, the inaccessibility of walls does not allow direct measurement of discontinuity surfaces by traditional geological methods. In such cases, data can only be obtained by statistical methods. Although this approach is significant and provides spatial meaning, it is ineffective for deterministic analysis. This paper provides a solution to this problem by applying digital terrestrial photogrammetric techniques employing a reamed bar, an aerostatic balloon and a helicopter. Results demonstrate that the accuracy and the quantity of geometrical and engineering–geological data coming from the photogrammetric survey, allow for numerical simulation of the relationship between rock elements as a function of their physical–mechanical properties and load conditions. The 3DEC code was chosen among the different methods available to model the discontinuous media through distinct elements. The proposed methodology was applied to a quarry located in the Carrara Marble District (the Apuan Alps, Italy), the largest and most exploited mining region in Europe. The economic value of the area required a detailed study of the presence of instability phenomena so that marble extraction could continue in safe conditions.

Ballistic behaviour of explosively shattered alumina and silicon carbide targets

The resistance offered by three ceramic materials of varying strength that have been subjected to explosive loading has been investigated by depth-of-penetration testing. Each material was completely penetrated by a tungsten carbide cored projectile and the residual penetration into a ductile aluminium alloy backing material was measured. The resulting ballistic performance of each damaged ceramic was found to be similar implying that the resistance offered to the projectile by the damaged ceramic is not dependent on the intrinsic strength properties of the intact material. This was taken as evidence that the important controlling parameter for enhancing the ballistic performance of a damaged ceramic material was not the strength of the ceramic but rather the fragment morphology.

An assessment of total RMR classification system using unified simulation model based on artificial neural networks

Engineering design has great importance in the cost and safety of engineering structures. Rock mass rating (RMR) system has become a reliable and widespread pre-design system for its ease of use and variety in engineering applications such as tunnels, foundations, and slopes. In RMR system, six parameters are employed in classifying a rock mass: uniaxial compressive strength of intact rock material (UCS), rock quality designation (RQD), spacing of discontinuities (SD), condition of discontinuities (CD), condition of groundwater (CG), and orientation of discontinuities (OD). The ratings of the first three parameters UCS, RQD, and SD are determined via graphic readings where the last three parameters CD, CG, and OD are estimated by the tables that are composed of interval valued linguistic expressions. Because of these linguistic expresions, the estimated rating values of the last three become fuzzy especially when the related conditions are close to border of any two classes. In such cases, these fuzzy situations could lead up incorrect rock class estimations. In this study, an empirical database based on the linguistic expressions for CD, CG, and OD is developed for training Artificial Neural Network (ANN) classifiers. The results obtained from graphical readings and ANN classifiers are unified in a simulation model (USM). The data obtained from five different tunnels, which were excavated for derivation purpose, are used to evaluate classification results of conventional method and proposed model. Finally, it is noted that more accurate and realistic ratings are reached by means of proposed model.

A new general empirical approach for the prediction of rock mass strengths of soft to hard rock masses

It is almost impossible to prepare representative cores of rock masses including discontinuities patterns for laboratory studies. To overcome these difficulties, researchers have focused on developing empirical equations for estimating of the stress–strain behavior of a rock mass, including measurements of the discontinuity patterns. As can be seen in the literature, the uniaxial compressive strength value of rock mass ( UCS RM ) can be estimated by reducing the uniaxial compressive strength of intact rock material ( UCS i ) based on the quality of a rock mass, represented by variables such as Rock Mass Rating ( RMR), Geological Strength Index ( GSI) and Q value. For this reason, a unique reducing curve form empirical equation has limited application and generally, cannot be applied to all kind of rock masses from particularly soft to hard rock masses. In this study, a new general empirical approach is constructed to estimate the strength of rock masses of varying hardness. The new empirical equations have been calibrated using data from five slope failures and four sets of uniaxial compressive strength data of rock masses. In the new empirical equations, the UCS i is considered not only to be a scale parameter used in the strength reduction but also used to adjust the degree of strength reduction in conjunction with elastic modulus of the rock material ( E i ). The disturbance factor on the rock mass is taken into consideration by two separate reduction factors applied to the Structure Rating ( SR) to capture increasing joint density, and to the s and m b parameters of the Hoek–Brown criterion, to decrease the degree of interlocking. Hence, non-interlocked (cohesionless under zero normal stress) rock masses such as spoil piles can also be modeled in the new empirical approach.

Modified Mohr–Coulomb criterion for non-linear triaxial and polyaxial strength of intact rocks

Triaxial or polyaxial strength of rocks is required while analysing many civil and mining engineering structures in rocks. Mohr–Coulomb criterion is the most widely used strength criterion in rock engineering problems. In its present form the criterion suffers from two major limitations. Firstly, it represents the strength of rock as a linear function of confining pressure. Secondly, the effect of intermediate principal stress is not considered by this criterion. In the present study, this criterion is modified to take into account the non-linearity and effect of intermediate principal stress on strength behaviour. Barton's [1] critical state concept for rocks has been employed for this purpose. The applicability of the proposed simple non-linear triaxial and polyaxial strength criteria has been verified by applying them to experimental results for the intact isotropic rock material available from literature and comparing the prediction with the other popular criteria in vogue. The agreement has been found to be excellent. The applicability of the concept to jointed rocks will be discussed in separate publication.

The synthetic rock mass approach for jointed rock mass modelling

This paper describes synthetic rock mass (SRM) modeling, a new approach for simulating the mechanical behavior of jointed rock mass. This technique uses the bonded particle model for rock to represent intact material and the smooth-joint contact model (SJM) to represent the in situ joint network. The macroscopic behavior of an SRM sample depends on both the creation of new fractures through intact material and slip/opening of pre-existing joints. SRM samples containing thousands of non-persistent joints can be submitted to standard laboratory tests (UCS, triaxial loading, and direct tension tests) or tested under a non-trivial stress path representative of the stresses induced during the engineering activity under study. Output from the SRM methodology includes pre-peak properties (modulus, damage threshold, peak strength, etc.) and post-peak properties (brittleness, dilation angle, residual strength, fragmentation, etc.). Of particular interest is the ability to obtain predictions of rock mass scale effects, anisotropy, and brittleness, properties that cannot be obtained using empirical methods of property estimation. This paper presents the theoretical background of the SRM approach along with some example applications.

Advances in sports drug testing: An overview

Advances in sports drug testing: An overview

On modeling failure of rubber-like materials

Strain energy increases unlimitedly with the increase of deformation according to traditional hyperelastic models of materials. This ‘growth condition’ is evidently unphysical because no real material can sustain large enough deformations without failure. To introduce failure in hyperelasticity we propose to replace the strain energy of any intact material, W, with a modified expression: ψ = Φ{ Γ(1/ m, 0) − Γ(1/ m, W m / Φ m )}/ m, where Φ is a material constant which sets a limit for the energy that can be accumulated during deformation, Γ is the upper incomplete gamma function, and m is a material constant controlling the sharpness of the transition to failure. The new formula for the strain energy is used to model failure of natural (NR) and styrene–butadiene (SBR) rubbers under plane stress conditions and the results are compared to the available experiments and other theories. The comparisons show that the proposed approach can be efficient for modeling failure in solids. The new theory allows reassessing the local criteria of material failure.

Influence of macro-fractures and micro-fractures on permeability and elastic wave velocities in basalt at elevated pressure

Fractures are ubiquitous on all scales in crustal rocks. The investigation of fractures and their influence on physical and transport properties of rocks is therefore essential for understanding of many key problems in seismology, volcanology and rock engineering. In crystalline rocks, pore water is primarily stored in and migrates through networks of cracks and fractures at all scales. It is therefore essential to know how fluid flow in such fracture networks responds to the elevated pressures found at depth. Here, we report results from an investigation of changes in fluid permeability, and associated changes in P-wave and S-wave velocities, at elevated effective pressure for intact, macro-fractured and micro-fractured samples of Seljadur basalt. In all cases, permeability decreases and both wave velocities increase with increasing effective pressure. Permeability decreases were smallest in the intact material (from approximately 10 −19 m 2 to 3 × 10 −20 m 2), intermediate in the micro-fractured material (from approximately 5 × 10 −17 m 2 to 1 × 10 −17 m 2) and largest in the macro-fractured material (from approximately 3 × 10 −15 m 2 to 9 × 10 −19 m 2). For a material containing both micro-fractures and macro-fractures, the closure of macro-fractures dominated the permeability reduction at low pressure, with the closure of micro-fractures exerting an increasing influence at higher pressure.

Failure analysis and risk management of a collapsed large wind turbine tower

Developing renewable energy is crucial as nations face the twin threats of global warming and a reduction in energy supplies. Wind turbines are one of the most promising sources of renewable energy in Taiwan. However, on September 28, 2008, Typhoon Jangmi struck Taiwan, bringing strong winds and heavy rainfall that collapsed a wind turbine tower located on the shore of Taichung Harbor. This study provides significant insights into, and lessons learned from, post-disaster inspection into the causes of tower failure during this typhoon. This event represented the first time that a wind turbine in Taiwan that had to be reconstructed after collapsing. To prevent similar accidents, the likely causal mechanisms are examined from the risk management perspective. Data for case analysis are collected from original tower design reports, the tower design code, construction records and documents, historical wind-speed data, structural tower analysis, and intact and fractured bolt material tests. Furthermore, similar accidents in other countries and their causes are reviewed to identify potential risk factors affecting the lifecycle of wind turbines.

Material model for finite element modelling of fatigue crack growth in concrete

Although fatigue damage of concrete is an important problem in structures subjected to cyclic loading, there are not many highcycle fatigue models available for use in conjunction with advanced concrete material models and nonlinear finite element analysis. The available models that are published in the literature (for instance [1]) usually deal with the low cycled fatigue when it is necessary to perform the numerical nonlinear analysis for all investigated cycles. This approach is definitely not applicable when it comes to high-cycle fatigue when it is usually necessary to consider millions of cycles. The available models (for instance [2]) for high-cycled fatigue are based on linear elastic fracture mechanics considerations and they are not readily applicable to the finite element analysis using the smeared crack approach.The three-dimensional fracture-plastic model [3] in the finite element software ATENA has been extended to capture fatigue damage in tension (however, the model can be easily modified to also consider damage from compressive and tensilecompressive loads). The damage can result in new cracks or growth of existing ones.To keep the material model as simple as possible, the implementation is based on a classical stress based model (S-N or Wöhler curve). The S-N criterion is translated into material damage, which is introduced into the material model on the basis of stress increments at each material point and the number of cycles. The S-N criterion is suitable to initiate damage into the intact material. However, in order to facilitate the necessary crack propagation and extension of a pre-existing damage an additional damage needs to be introduced. It is advantageous to base this damage not on stress cycles but rather on the cycles of crack opening displacements (delta COD). The paper will present the formulation of the new model for the high-cycle fatigue in a form that is suitable for the smeared crack model formulation and the finite element analysis. The model behaviour will be documented on small theoretical examples as well as by comparison with experimental data.

Nano-scale quasi-melting of alkali-borosilicate glasses under electron irradiation

Quasi-melting of micro- and nano-samples during transmission electron microscope irradiation of glassy materials is analysed. Overheating and true melting by the electron beam is shown not to be an explanation due to the ultra-sharp boundary between transformed and intact material. We propose that the observed fluidisation (quasi-melting) of glasses can be caused by effective bond breaking processes induced by the energetic electrons in the electron beam. The bond breaking processes modify the effective viscosity of glasses to a low activation energy regime. The higher the electron flux density the lower is the viscosity. Quasi-melting of glasses at high enough electron flux densities can result in shape modification of nano-sized particles including formation of perfect beads due to surface tension. Accompanying effects, such as bubble formation and foil bending are revisited in the light of the new interpretation.

Dynamic fragmentation of blast mitigants

Experimental evidence from a wide range of sources shows that the expanding cloud of explosively disseminated material comprises “particles” or fragments which have different dimensions from those associated with the original material. Powders and liquids have often been used to surround explosives to act as blast mitigants, and this is the main driver for our research. There are also many other areas of interest where an initially intact material surrounding an explosive charge is dynamically fragmented into a distribution of fragment sizes. Examples of such areas include fuel air explosives and enhanced blast explosives as well as quasi-static pressure mitigation systems, and our studies are thus also relevant to these applications. In this paper, we consider the processes occurring as an explosive interacts with a surrounding layer of liquid or powder and identify why it is important to model these processes as a multiphase material problem as opposed to a single phase, single material velocity problem. We shall present results from this class of numerical modelling. In this paper we shall explore what determines the particle or fragment size distribution resulting from explosive dissemination of a layer of material and discuss reasons why clouds from disseminated liquids and powders look similar. We shall support our analysis with results from recent explosives trials and introduce early results from some ongoing small scale explosive mitigation experiments.

Deformation, fracture, and fragmentation in brittle geologic solids

A model is developed for mechanical behavior and failure of brittle solids of geologic origin. Mechanisms considered include elastic stretch and rotation, thermal expansion, and deformation associated with micro-cracks. Decohesion on preferred cleavage planes in the solid, and subsequent effects of crack opening and sliding, are modeled. Explicit volume averaging over an element of material containing displacement discontinuities, in conjunction with the generalized divergence theorem, leads to an additive decomposition of the deformation gradient into contributions from thermoelasticity in the intact material and displacement jumps across micro-cracks. This additive decomposition is converted into a multiplicative decomposition, and the inelastic velocity gradient is then derived in terms of rates of crack extension, opening, and sliding on discrete planes in the microstructure. Elastic nonlinearity at high pressures, elastic moduli degradation from micro-cracking, dilatancy, pressure- and strain rate-sensitive yield, and energy dissipation from crack growth and sliding are formally addressed. Densities of micro-cracks are treated as internal state variables affecting the free energy of the solid. The mean fragment size of particles of failed material arises from geometric arguments in terms of the evolving average crack radius and crack density, with smaller fragments favored at higher loading rates. The model is applied to study granite, a hard polycrystalline rock, under various loading regimes. Dynamic stress–strain behavior and mean fragment sizes of failed material are realistically modeled. Possible inelastic anisotropy can be described naturally via prescription of cleavage planes of varying strengths.

Biomineralization of calcium phosphate on human hair protein film and formation of a novel hydroxyapatite-protein composite material.

Human hair protein can be used not only as a totally biodegradable material but also as a "self-originated" material, which may avoid an undesirable immune reaction, if it has been prepared from a certain individual and implanted into the same person. In this study, a novel organic-inorganic composite, which contains human hair proteins and hydroxyapatite, was investigated as biomineral-scaffolding materials. The human hair protein was extracted by our original "Shindai method" (Nakamura et al., Biol Pharm Bull 2002;25:569-572; Fujii et al., Biol Pharm Bull 2004;27:89-93). The extracts were exposed to CaCl(2) solution for fabrication into flat films, which mainly consisted of alpha-keratin. After washing with distilled water, approximately 3 Ca(2+) ions per 1 keratin molecule bound to the film. The Ca(2+)-binding was slightly sensitive to the ionic strengths, and only Mg(2+) inhibited binding of Ca(2+). A composite of the human hair protein and calcium phosphate was prepared via alternate soaking processes using CaCl(2) and Na(2)HPO(4) solutions. As the soaking cycle proceeded, the film weight increased and its color became white, indicating successful deposition of calcium phosphate. The diameters of deposited calcium phosphate particles were about 2-4 microm. The proteins were not solubilized and degraded during the soaking processes. FTIR and WAXD analyses indicated that calcium phosphate was first deposited as amorphous, then transformed into crystalline monohydrogen calcium phosphate during the earlier soaking cycle, and, via octacalcium phosphate, finally converted into hydroxyapatite after 20 cycles. The present human hair protein/hydroxyapatite composite film is a "self-originated" and also an intact proteinaceous material without chemical modification, and thus, a promising material for hard tissue engineering.