Sample Width Research Articles

Superelasticity of Geometrically Graded NiTi Shape Memory Alloys

A stress plateau with a strain of 5–8% normally occurs during the stress-induced martensite transformation (SIM) of NiTi shape memory alloys. Within the stress plateau, the correlation between the stress and strain is lost, which limits their application in certain fields which require accurate control of inelastic deformation. In order to address this limitation, a series of step-like NiTi samples with graded cross-sectional area were designed and fabricated. Multiple stress plateaus were achieved by varying the sample width and adjusting the number of steps; for instance, two and three stress plateaus were obtained in the samples with two and three steps, respectively. Also, linear force–strain response was obtained by changing gradually the width of the samples. The functional stability of the geometrically graded samples was significantly improved by incomplete recrystallization annealing (600 °C) followed by low-temperature (250 °C) aging treatment. The incompletely recrystallized specimens contained many dislocations and grain and sub-grain boundaries, which promoted the uniform precipitation of Ni4Ti3 nanoparticles during aging treatment. The homogeneously and densely dispersed Ni4Ti3 nanoparticles were able to strengthen the matrix considerably and prevent plastic activities during stress-induced martensite transformation. As a result, the functional stability of the geometrically graded NiTi samples was much improved. After aging at 250 °C for 120 h, all the samples showed a small residual strain of <1.0% after 20 loading–unloading cycles.

Computational Fracture Evolution Analysis of Steel-Fiber-Reinforced Concrete Using Concrete Continuous Damage and Fiber Progressive Models.

The process of concrete cracking is a common problem because the first micro-cracks due to the loss of moisture may appear even before the concrete is loaded. The application of fracture mechanics allows for a better understanding of this problem. Steel-fiber-reinforced concrete (SFRC) samples with a notch were subjected to a three-point bending test, and the results for crack energy were used to analyze the concrete's material properties. In this paper, an experimental and numerical analysis of SFRC with rapid changes in the force (F) crack mouth opening displacement (CMOD) curve (F-CMOD) is presented. In order to obtain the relevant F-CMOD diagrams, three-point bending tests were carried out with non-standard samples with a thickness equal to one-third of the width of standard samples. For analysis purposes, crimped steel fibers were adopted. A probabilistic analysis of the most important parameters describing the material in question, such as peak strength, post-cracking strength, crack mouth opening displacement (CMOD), fracture energy, and the post-cracking deformation modulus, was conducted. The tests and the analysis of their results show that the quasi-static numerical method can be applied to obtain suitable results. However, significant dynamic effects during experiments that influence the F-CMOD curves are hard to reflect well in numerical calculations.

Measurement techniques for self-sensing cementitious composites under flexure

Intrinsic self-sensing concrete has gained substantial interest recently as a promising construction material for smart structures. Most of the research focuses on testing their sensing behaviour under pure compression, but in practice, damage to concrete structures due to bending is more commonly seen. It is thus necessary to also test the sensing performance of the composites under flexural loading. Due to the variation of the stress distribution in a concrete element subject to bending, the influence of the geometry of electrodes on measured results is more complex. This study investigated the self-sensing behaviour of prismatic graphite-cementitious specimens under three- and four-point bending with different electrode placements. Composites were tested both in the elastic and plastic range by applying cyclic and monotonic flexural loading. Prisms with different sample depth, sample width, electrode penetration and electrode diameter were further modelled numerically using Finite Element Analysis (FEA) to study the electrical behaviour. Experimental results show that to obtain accurate measurements for composites under flexure, the electrodes need to be at close spacings with shallow penetration at the tensile side of the specimen in order to measure behaviour in the tensile zone. An equation for the relationship between the measured resistance and the geometry variables has been found through numerical simulation that can estimate the influence zone within the sample and hence enable optimisation of the electrode placement for self-sensing cementitious composites under flexure.

The effect of oxygen and water on the provision of crack closure in bacteria-based self-healing cementitious composites

This study determined the impact of oxygen and water on the crack healing performance of bacteria-based self-healing cementitious composites (BBSHCCs). Oxygen and water are considered essential to BBSHCCs using non-ureolytic bacteria, but in practice, the availability of either, for even short periods of time, cannot be guaranteed in the immediate aftermath of a crack forming. In this study, four healing regimes, (i) daily wet-dry cycle, (ii) weekly wet-dry cycle, (iii) semi-submerged and (iv) a deposition medium, were utilised to compare the impact of oxygen and water on the performance of BBSHCCs. Furthermore, an oxygen-releasing coating (ORC) containing calcium peroxide was evaluated and used in this study to further understand the function of oxygen in bacteria-based self-healing. Results showed that bacteria-based self-healing was only effective in wet conditions that also permit oxygen to penetrate the crack. Where there was a possibility for the composite to dry, after cracking, despite being wet some of the time the self-healing was far less efficient. It was observed that an overdose of nutrients and calcium in the healing environment resulted in early rapid healing, followed at a later stage by the dissolution of the initially formed precipitates. Moreover, it was found that the ORC contributed significantly to the recovery of both crack width and water tightness of samples. These findings will aid the development of appropriate test standards for self-healing cementitious composites and for the design and implementation of such cementitious composites in practice.

Preparation and characterization of lignin containing cellulose nanofiber from moso bamboo via acidified choline chloride/ethylene glycol pretreatment combined with homogenization

Lignin is one of the main components of lignocellulose, which is conducive to controlling and optimizing the performance of cellulose nanofiber. In the present work, lignin containing cellulose nanofiber (LCNF) was prepared from moso bamboo by acidified choline chloride/ethylene glycol (acidified ChCl/EtG) pretreatment combined with high-pressure homogenization. The cellulose-rich residue with gradient lignin retention (9.10–31.12%) was obtained from bamboo pretreatment under different reaction conditions. The residue was nanofibrillated into LCNF via high-pressure homogenization. The results showed that the width of LCNF samples was 6–30 nm and its width was tunable by adjusting the lignin content in cellulose-rich residue. Meanwhile, the lignin was evenly distributed in the LCNF suspension, endowing LCNF with UV shielding capability. Moreover, the LCNF suspension was stable at concentrations above 0.1 wt%, which was prone to long-term preservation and utilization. The presence of a certain amount of lignin was also able to enhance the mechanical properties of LCNF films, which can provide a prospective future for bamboo and LCNF valued-added utilization.

Interlaminar shear modulus of cardboard obtained by torsional and flexural vibration tests

Abstract The interlaminar shear modulus of cardboards was measured using torsional vibration (TV) and flexural vibration (FV) methods. In the TV method, the sample widths were decreased during the tests, and the interlaminar and in-plane shear moduli were determined using the data obtained based on the different widths. By contrast, in the FV method, the resonance frequencies from the first to third FV modes were measured using samples of various lengths, and the interlaminar shear modulus and Young’s modulus in the length direction were calculated using Timoshenko’s vibration theory. In addition to the experiment, modal analyses based on the finite element (FE) method were performed, and the sample configurations used to accurately obtain the interlaminar shear modulus were experimentally and numerically investigated. The TV method did not allow the interlaminar shear modulus to be obtained appropriately because the vibration behavior often deviated from that theoretically derived by the TV equation. By contrast, the FV method allowed the interlaminar shear modulus to be obtained appropriately for a wide range of sample lengths.

Desiccation cracking behaviour of a vegetated soil incorporating planting density

Vegetation has been widely used in geotechnical engineering. However, desiccation cracking in vegetated soils is very common and often neglected. This study aims to investigate desiccation cracking behaviour of a vegetated soil considering different planting densities. The evolution of water content and surface crack pattern during drying is monitored. Experimental results show that during the early stage of drying, the evapotranspiration rate of the vegetated sample with a smaller planting density is slightly less than the evaporation rate of the bare soil sample, and the evapotranspiration rate increases with increasing planting density. In the vegetated samples, cracks initiate almost simultaneously. The larger the planting density, the more the crack initiation points and the smaller the cracking water content. In terms of the final crack pattern, both the surface crack ratio and the average crack width of vegetated samples are smaller than those of the bare sample. As the planting density increases, there are more fine and thin cracks. However, increasing planting density does not lead to a continuous decrease in cracking degree. It is necessary to select an appropriate planting density (about 24 g/m2 in this study) to maximize the inhibitory effect of vegetation on soil desiccation cracking.

Reconstruction of Material Inhomogeneity Profile Using Partially Filled Rectangular Waveguide Measurements

This article presents a novel technique to reconstruct the inhomogeneity profiles of the material using partially filled rectangular waveguide (RWG) measurements. Variation in the sample width is developed to obtain the required independent scattering parameters for accurately reconstructing the inhomogeneity profiles. The electromagnetic parameters of the inhomogeneous sample are obtained, minimizing the difference between the measured and the theoretically calculated scattering parameters. For the first time in this article, the scattering parameters of the inhomogeneous material partially loaded in the RWG are theoretically calculated using the hybrid of mode matching and Taylor’s series expansion. A prototype of the measurement system is fabricated for experimental verification. Through comprehensive examples, experimental verifications are performed for the three types of inhomogeneous materials. The validity and accuracy of the proposed method are verified by comparing the results obtained by the RWG methods. The suggested technique is less expensive and more straightforward than the previously developed RWG method, which uses multiple waveguides and requires a single-time calibration.

DEM investigation on the size effect in the fragmentation of intact aggregates

In this work, the size effect in the fragmentation strength of cylindrical alumina aggregate under quasi-static diametrical loading is investigated by performing Discrete Element Method (DEM) simulations. It is found that tensile stress concentration develops in the inner margin of the damage zone, ultimately leading to the emergence and propagation of diametrical crack and thus the catastrophic splitting of the compressed aggregate. Both the fragmentation strength and the dimensionless damage zone size (normalized by aggregate diameter) decrease to limit values, and the latter is around 0.1. It is found that the obtained limit value of fragmentation strength is approximately equal to the tensile fracture strength of the corresponding rectangular sample having two equal-length side cracks with length being 0.1 times the sample width. The DEM simulations thus suggest that the formation of damage zones adjacent to the loading points would induce the size effect in the fragmentation of intact aggregate.

Dispersive contour-path algorithm for the FDTD analysis of a periodic structure at oblique incidence

Arbitrarily-shaped dispersive media can be treated with the dispersive contour-path (DCP) FDTD method. We extend the DCP-FDTD method for the analysis of a periodic structure to the case at oblique incidence. A trapezoidal recursive convolution technique is used to incorporate dispersive media into the DCP-FDTD method. The transmission characteristics of a metallic cylinder array are evaluated and discussed. It is found that the present method gives almost the same solution as the conventional staircase FDTD method, even with a sampling width five times as large as the conventional counterpart.

Statistical analysis of biomechanical properties and size of the sternum and its fracture risk in a Japanese sample

ObjectiveSternal fractures can have life-threatening complications. To understand chest injury mechanisms, sufficient data regarding the mechanical properties and structure of the sternum are required. The aim of this study was to examine the mechanical properties and size of the sternum in a Japanese forensic sample. Materials and methodsSterna were obtained from 120 Japanese dead bodies of known age and sex. The sample thickness (ST) and the sample width (SW) were measured using a computed tomographic image. Three-point-bending tests were conducted using a three-point-bending apparatus to assess the fracture load (FL) of the sample. Then, the flexural strength (FS) was calculated and the natural logarithm of FL (ln FL) and FS (ln FS) were also calculated. ResultsThe values of ST, ln FL, and ln FS for male samples were significantly greater than those for female samples. Both ln FL and ln FS had significant negative correlations with age regardless of sex; the Pearson product-moment correlation coefficients were larger for female samples than for male samples. Although age was significantly negatively correlated with SW in female samples, there was no significant correlation between age and SW in male samples. No significant correlations were found between age and ST regardless of sex. ConclusionThis is the first study to present quantitative data on the biomechanical properties of the sternum. Because of the smaller sternal strength of elderly women, it is especially important for them to avoid the risk of sternal fractures.

Failure Characteristics of the Water-Resisting Coal Pillar under Stress-Seepage Coupling and Determination of Reasonable Coal Pillar Width

Groundwater inrush hazard has always been a great threat to the construction of vertical shafts in coal mines. Generally, the failure of the water-resisting coal pillar under coupled stress-seepage conditions around the vertical shaft is the main reason for the generation of the water inrush channel. In order to understand the mechanical behaviors of the water-resisting coal pillar, the strength of typical coal affected by the size and water content was investigated, and the stress sensitivity of permeability was investigated by a stress-seepage coupling test. The stress field and deformation of the water-resisting coal pillar were investigated by numerical simulation, the stability of the water-resisting coal pillars with different widths was evaluated, and the reasonable width of the coal pillars under coupled stress-seepage condition was determined. Results show that the water content and coal pillar width have a great influence on the mechanical characteristics of coal samples. Under the conditions of lower water content and larger coal sample width, the coal sample presents higher strength, smaller axial deformation, smaller permeability and porosity, and weak sensitivity to stress. The simulation results show that the boundary of the main roadway at the end of the coal pillar is dominated by tensile stress, and fractures can significantly contribute to the destruction of coal pillars. With the increase in the width of the water-resisting coal pillar, the internal damage variable, maximum tensile stress, porosity, and average water flow velocity of the coal pillar decrease, which reduces the risk of water inrush and improves the safety of the water-resisting coal pillar. An evaluation model of the reasonable width of the water-resisting coal pillar under the stress-seepage coupling was proposed, and the model was verified by the shear slip law and experimental results. This study provides theoretical and experimental guidance for the risk management of groundwater inrush disaster during the construction of vertical shafts in coal mines.

Confinement-Induced Chiral Edge Channel Interaction in Quantum Anomalous Hall Insulators.

In quantum anomalous Hall (QAH) insulators, the interior is insulating but electrons can travel with zero resistance along one-dimensional (1D) conducting paths known as chiral edge channels (CECs). These CECs have been predicted to be confined to the 1D edges and exponentially decay in the two-dimensional (2D) bulk. In this Letter, we present the results of a systematic study of QAH devices fashioned in a Hall bar geometry of different widths under gate voltages. At the charge neutral point, the QAH effect persists in a Hall bar device with a width of only ∼72 nm, implying the intrinsic decaying length of CECs is less than ∼36 nm. In the electron-doped regime, we find that the Hall resistance deviates quickly from the quantized value when the sample width is less than 1 μm. Our theoretical calculations suggest that the wave function of CEC first decays exponentially and then shows a long tail due to disorder-induced bulk states. Therefore, the deviation from the quantized Hall resistance in narrow QAH samples originates from the interaction between two opposite CECs mediated by disorder-induced bulk states in QAH insulators, consistent with our experimental observations.

Validation of gas flow experiments for porous media by means of computer simulations

A profound understanding of gas flow in porous media is of great interest for various technological and scientific fields. Its investigation by laboratory measurements, however, poses several challenges. In particular, the determination of macroscopic flow parameters from pressure and gas flow measurements is prone to various error influences, some of which are very difficult to analyze experimentally. Computer simulations are a solution in this context as they facilitate modifications of the underlying geometry and boundary conditions in a flexible way. Here we present a simulation framework for the analysis of a recent experiment for determining the Knudsen diffusion coefficient and viscous permeability of various porous granular materials. By combining the finite element method with analytical models and other numerical methods, we were able to identify previously neglected physical effects that increase the uncertainty of the measurements. In particular, the porosity increase due to finite sample dimensions, in a layer of about a grain diameter thickness near the container wall, creates a deviation of the measured pressure gradient. This deviation amounts to ca. 5% for a sample width of about 100 grains and a porosity of 0.5, and is indirectly proportional to the porosity. The second most prominent error source, the sample support sieve, causes a slight constriction of the flow volume. Simulations of this effect show an error around 4%–7%, dependent on the grain size. Based on these findings we recommend an overall sample dimension of 100 grains or larger. As an example of failures of the sample homogeneity, we elaborate how channels through the sample influence the flow properties. Respective suggestions for keeping all discussed effects negligible are discussed in detail. Our methodology demonstrates how the combination of finite element computations with analytical representations of the involved macroscopic parameters can assess the validity and accuracy of laboratory experiments.

Experimental study on coupled combustion of PMMA counter-directional flame spread in the horizontal direction

An experimental study was carried out to address the effects of coupled combustion, and sample widths on counter-directional flame spread over poly(methyl methacrylate) (PMMA) boards in the horizontal direction. Typical flame propagation parameters were observed and analyzed, including flame form, flame front, characteristic angles, rate of spread, and radiative heat flux density. Experimental results showed that the counter-directional fire propagation process could be divided into four stages based on the flame morphology variation, and the evolution of the flame front was presented as well. The characteristic angles, defined as half of the flame front angle, show the velocity variation between the side-edge and center flame at different spread phases. Compared with unilateral flame spread, the radiative heat flux density for the counter-directional flame spread grows faster, and the maximum value is about twice. Moreover, the maximal radiative heat flux increases for a wider sample, and a positive linear relationship exists between the dimensionless mass loss rate and characteristic angle against the breadth length ratio. The research outcomes of this study offer a better understanding of the counter-directional flame spread mechanism from aspects of scale change and heat transfer.

Ex vivo bovine liver nonlinear viscoelastic properties: MR elastography and rheological measurements

IntroductionKnowledge of the nonlinear viscoelastic properties of the liver is important, but the complex tissue behavior outside the linear viscoelastic regime has impeded their characterization, particularly in vivo. Combining static compression with magnetic resonance (MR) elastography has the potential to be a useful imaging method for assessing large deformation mechanical properties of soft tissues in vivo. However, this remains to be verified. Therefore this study aims first to determine whether MR elastography can measure the nonlinear mechanical properties of ex vivo bovine liver tissue under varying levels of uniform and focal preloads (up to 30%), and second to compare MR elastography-derived complex shear modulus with standard rheological measurements. MethodNine fresh bovine livers were collected from a local abattoir, and experiments were conducted within 12hr of death. Two cubic samples (∼10 × 10 × 10 cm3) were dissected from each liver and imaged using MR elastography (60 Hz) under 4 levels of uniform and focal preload (1, 10, 20, and 30% of sample width) to investigate the relationship between MR elastography-derived complex shear modulus (G∗) and the maximum principal Right Cauchy Green Strain (C11). Three tissue samples from each of the same 9 livers underwent oscillatory rheometry under the same 4 preloads (1, 10, 20, and 30% strain). MR elastography-derived complex shear modulus (G∗) from the uniform preload was validated against rheometry by fitting the frequency dependence of G∗ with a power-law and extrapolating rheometry-derived G∗ to 60 Hz. ResultsMR elastography-derived G∗ increased with increasing compressive large deformation strain, and followed a power-law curve (G∗ = 1.73 × C11−0.38, R2 = 0.96). Similarly, rheometry-derived G∗ at 1 Hz, increasing from 0.66 ± 1.03 kPa (1% strain) to 1.84 ± 1.65 kPa (30% strain, RM one-way ANOVA, P < 0.001), and the frequency dependence of G∗ followed a power-law with the exponent decreasing from 0.13 to 0.06 with increasing preload. MR elastography-derived G∗ was 1.4–3.1 times higher than the extrapolated rheometry-derived G∗ at 60 Hz, but the strain dependence was consistent between rheometry and MR elastography measurements. ConclusionsThis study demonstrates that MR elastography can detect changes in ex vivo bovine liver complex shear modulus due to either uniform or focal preload and therefore can be a useful technique to characterize nonlinear viscoelastic properties of soft tissue, provided that strains applied to the tissue can be quantified. Although MR elastography could reliably characterize the strain dependence of the ex vivo bovine liver, MR elastography overestimated the complex shear modulus of the tissue compared to rheological measurements, particularly at lower preload (<10%). That is likely to be important in clinical hepatic MR elastography diagnosis studies if preload is not carefully considered. A limitation is the absence of overlapping frequency between rheometry and MR elastography for formal validation.

Physiochemical Properties Characterization of Local Sesame Seeds (Sesamum indicum L.) Grown in Kurdistan Region

The aim of this investigation to determine the physical and chemical properties of three sesame seeds sample to see the differences between mixed and the sieved sesame seed and which one is better and which sesame seed has the best physical and chemical properties: which were taken from sharzoor in Sulaymaniyah (S, mixed brown), Akre in Duhok (A, mixed brown) and Mala Omar in Hawler (MO, mixed brown). For each sample two parts were taken to undergoes study the first one as a mix and other part was sieved in three different mesh size sieve (1.50, 1.35, 1) mm, then three sieves divisions of sesame seed size were obtained, Large (L), Medium (Med), Small (Sm) and the three dimension of all sesame seeds parts were measured by applying Digital Dial Caliper instrument. The dimensions length (L,mm), width(W,mm) and Thickness(T,mm) were measured for determine of geometrical properties of sesame seeds sample and all samples color was as a mix of brown color such as volume (V, mm^3), sphericity (S, %,), arithmetic diameter (Da, mm), geometric diameter (Dg, mm), apparent density (𝜌d, kg/m3), transverse surface area (At, mm2) and flat surface area (Af, mm2) also weight of 100 seeds (g) was estimated. The result of the study indicated that Akre (A) sesame seed sample length for mix and med has higher value 3.33 and 3.08 mm respectively. The Mala Omar sample width for all mix and other parts large, small reported higher measurement 1.75, 1.86, 1.27mm respectively. The thickness of the mix and large parts of Sharazoor reported higher measurement 0.90 and 0.91 mm while. Mala Omar Sample C3 of sesame seed scored highest moisture content 4.909%, while Akre sample B1 recorded the lowest moisture content. The large part of S, A and MO sesame seed samples firstly with higher fiber content 16.141, 17.56, 18.34 respectively.

Lüders band evolution in geometrically graded NiTi plates

This study investigated the process of the Lüders band formation and propagation within geometrically graded plate samples of a pseudoelastic NiTi during the stress-induced martensitic transformation by means of digital image correlation full-field strain measurement. The geometrically graded plate samples had parabolic width profiles in concave and convex forms along the length. Such sample geometries created a situation of progressively increasing applied load and a continuous variation of the sample width during the process of the stress-induced transformation. The size (along the sample length direction) of the Lüders band front transition zone was found to remain unchanged with variation of the sample width during the process, but the local strain rate across the transition zone was varied. The transition zone of the martensite Lüders band during the forward transformation was wider than that of the austenite Lüders band on the reverse transformation, and the local strain rate was lower than that of the latter.

Change Laws of Pore-Fracture Structure of Coal under High-Temperature Steam Shock.

Injecting steam into coal seam is an important means to accelerate gas desorption and improve gas extraction efficiency. However, the change law of pore-fracture structures of coal after high-temperature steam shock (thermal shock) is still unclear. Through this study, pore-fracture structures of coal samples before and after thermal shock were compared and analyzed based on the experimental methods of surface pore and fracture extraction, scanning electron microscopy (SEM), and nuclear magnetic resonance (NMR) spectroscopy. The results show that after thermal shock, the surface porosity, max equivalent fracture width, fracture lengths, fracture number, and probability entropy of coal samples increased significantly, and the increment of bituminous coal was greater than that of anthracite. This indicates that thermal shock can promote the development of coal pores, which is significantly better for bituminous coal than anthracite. A SEM analysis reveals that fractures tend to appear at the interface between minerals and coal matrix. The NMR analysis demonstrates that the absolute increment of micropores is the largest, followed by that of mesopores, and that of macropores is the smallest. The increase of porosity in coal shows pore enlargement and penetration, which enhance the connectivity between the pores, thus providing a smoother channel for methane migration. Heterogeneous distribution of mineral components with different thermal expansion coefficients as well as the temperature gradient is the fundamental mechanism behind thermal stress-induced porosity development. The research results provide theoretical support for enhanced gas extraction technology by high-temperature steam injection into coal seams.

Br-doping mediated band-gap engineering contributed Bi/Bi2O2CO3 nano-platelets with enhanced photocatalytic performance

Photocatalyst modification by energy level engineering is of great significance for the generating of active free radical. In this work, a novel strategy was employed to construct Br-doped Bi2O2CO3 followed by in situ reduction deposited Bi nanoparticles on the surface of Bi2O2CO3 component. Therein, the doping of Br regulated the energy level structure of Bi2O2CO3. The characterization of SEM and TEM intuitively displayed the morphology changes among Bi2O2CO3, Br-Bi2O2CO3 and Br-Bi/Bi2O2CO3 in size and thickness, while XRD illustrated that the decrease in shape was consistent with the increase in the half-peak width of the Br-doped samples. The Tauc spectrum verified that the bandgap of Br-Bi/Bi2O2CO3 nanosheets was obviously narrowed, and after Bi nanoparticles were deposited on the surface of Bi2O2CO3 by in-situ reduction of Bi3+ with glucose, the absorption of visible light was enlarged distinctively. Excitingly, the kinetic constant of Br-Bi/Bi2O2CO3 sample was 7.22 times higher than that of Bi2O2CO3, showed excellent photocatalytic performance on degrading of tetracycline. The liquid chromatography-mass spectrometry (LC-MS) was employed to deduce the possible degradation routes, and then the toxicity of tetracycline and its degradation intermediates were analysed based on quantitative structure activity relationship (QSAR).