Minute Cracks Research Articles

Impact of Cross‐Linking on the Physicochemical and Physiological Characteristics of Barnyard Millet (Echinochloa frumentacea) Grains Starch

Barnyard millet starch (Echinochloa frumentacea) has been investigated for its potential in drug delivery systems due to its unique properties. This study examined the physicochemical and physiological properties of cross‐linked barnyard millet starch (BMS) using varying concentrations of sodium tripolyphosphate (STPP). Physicochemical and physiological properties of the cross‐linked starches are analyzed. Cross‐linking resulted in reduced swelling capacity and solubility of starch samples. Morphological analysis revealed rough surfaces with cavities and minute cracks in cross‐linked starches. Acute and sub‐acute toxicity studies in test animals indicated no adverse effects, with LD50 values within acceptable limits at 2000 mg kg−1. Hematological, biochemical, and lipid profiles showed no significant alterations compared to the control group. The study demonstrated a low acute toxicity level and favorable safety profile for STPP‐cross‐linked starch. These findings highlighted the potential of cross‐linked barnyard millet starch as a carrier in drug delivery system and for food applications. This study supports the potential of cross‐linked barnyard millet starch in pharmaceutical formulations.

Fatigue performance of stud connectors in joints between top slabs and steel girders with corrugated webs subjected to transverse bending moments

Steel-concrete composite box girders with corrugated steel webs (CSWs) are broadly used in bridge engineering, in which the joints between top RC slabs and steel girders with CSWs are usually subjected to transverse bending moments caused by off-center vehicle loads. Stud connectors arranged in the joints usually bear repeated pull-out forces in this case and are prone to fatigue failure. Therefore, two reduced scale joints between top slabs and weathering steel girders with CSWs were designed and tested, on which variable amplitude fatigue loads were applied to investigate the fatigue performance of studs incorporated in the joints. The two joints presented similar fatigue behavior, i.e., cracks of not more than 0.26 mm in width appeared on the surface of the top slab during the fatigue loading, and the separation of the top RC slabs and the top girder flanges was observed; meanwhile, minute cracks developed along the welds connecting the CSW with the bottom girder flange, and the stiffness of the joints gradually decreased due to the accumulation of fatigue damage. The two joints underwent 2,650,000 and 2,103,600 load cycles respectively before fatigue failure occurred. After partially demolishing the RC slabs, several welded head studs in the joints were observed fractured at the roots and detached from the top girder flange. Whereafter, finite element (FE) models referring to the test joints were developed and analyzed, and the effect of the wave height (WH) of the CSW and the transverse row spacing (TRS) of studs on the distribution of pull-out forces among studs was investigated. It showed that the pull-out force bore by each stud in the joint was distributed unevenly even in the same row. Then, a modification factor α was introduced to revise the pull-out forces of studs calculated in the theoretical method. An equation to determine the factor was fitted, considering the effect of the WH of the CSW and the TRS of studs. Finally, the detail category for studs bearing pull-out forces in the joints was discussed based on the experimental results and the collected test data, and it was preliminarily recommended studs subjected to pull-out forces can be classified into detail category 45 specified by Eurocode 3 in fatigue design.

Macro- and micromechanical characteristics and energy evolution law of micro/nano carbon fibre grouting samples

This study comprehensively explores the macro- and micromechanical attributes and energy evolution dynamics of micro/nano carbon fiber (CF) specimens. The investigation centers on a graded sand gravel grouting specimen, aiming to determine the optimal CF content through uniaxial compression tests conducted on samples containing 0.0 %, 0.5 %, 1.0 %, and 1.5 % CF. Utilizing CT and PFC2D simulation analyses, we establish the interrelation between micro- and macromechanics. The findings reveal similar failure modes across CF samples with varying contents, predominantly marked by shear failure in the principal crack of the inclined section, accompanied by proximal secondary cracks. The post-peak stress–strain curves exhibit notable divergences. Specifically, with increasing CF content, the total strain energy, elastic strain energy, and dissipated energy of the CF samples initially decline, subsequently rise, and then diminish once more. Furthermore, the 1.0%CF sample demonstrates heightened dissipated energy, uniaxial compressive strength, and elastic modulus in contrast to the 0%CF sample, showcasing superior macroscopic mechanical properties and enhanced toughness. A staged microcrack evolution unfolds, delineating defect initiation, pore evolution, crack development, and crack penetration stages. The non-uniform distribution of CF and sand gravel profoundly influences the propagation trajectory of minute cracks. Additionally, the failure modes and energy evolution trends from both models closely mirror experimental outcomes. The reinforcing characteristics and crack-resistant attributes of CF usher the transition from brittle failure (0%CF) to ductile failure (1.0%CF). PFC simulations highlight hysteresis in the model's damage and failure, underscoring CF's role in restraining grouting sample failure and shifting it from brittle (0%CF) to ductile (1.0%CF) failure, thus accentuating CF's pivotal role in impeding crack propagation. These findings furnish invaluable theoretical insights for bolstering grouting reinforcement in fractured rock masses.

Efficacy and accuracy of Invisalign attachments: an updated systematic review

Background: The primary purposes of Invisalign® technology are to treat minor to moderate crowding problems and patch up minute cracks. But more recent research and development have made it possible to cure more complex malocclusions. Although the accuracy of Invisalign-assisted orthodontic tooth movements has been researched, the effectiveness of various attachment methods and other aligner factors has not been thoroughly assessed. This study aimed at assessing the accuracy and efficacy of the Invisalign attachment mechanism as described in the most recent publications. Method: A systematic assessment of research examining the precision and efficacy of Invisalign attachments between 2019 and 2022 was performed employing Google Scholar and PubMed databases. The keywords were "efficacy, accuracy, Invisalign attachments, clear aligners, Invisalign®, invisible orthodontics, treatment results," which were used in various combinations. Original research describing the precision and effectiveness of the Invisalign attachments and full-text papers met the criteria for inclusion. Results: Only 8 articles out of 14 met the requirements for inclusion. Six studies were retrospective, one was prospective observational research, and one was a case-series investigation. Together, they involved 621 people. Even though Invisalign® orthodontic treatment is widely used, aside from the non-extraction treatment of mild to moderate malocclusions in non-growing patients, there are presently no definitive recommendations on additional indications of the system based on trustworthy scientific evidence. Invisalign attachments, transparent aligners, and full-text studies demonstrated its efficacy in the non-extraction correction of mild to moderate malocclusions in patients who were not growing. Conclusion: Despite the large number of studies examined in this study, evaluations of treatment results need to be cautious due to the significant heterogeneity. For a broad spectrum of malocclusions and expanding patient populations, further research involving parallel arm RCTs or carefully planned prospective trials is necessary to develop solid clinical recommendations.

Does periodontal ligament removal using natural proteolytic enzymes alter the surface structure and microhardness of cementum of avulsed tooth? An in vitro analysis

Introduction: Surface treatment of avulsed tooth must be directed towards the debridement of necrotic periodontal fibers while having no effect on the cementum microhardness. The role of proteolytic enzymes on the periodontal ligament (PDL) surface and hardness of cementum has not been investigated in the literature. Aim: The present study aimed to evaluate the effect of 5.25% sodium hypochlorite (NaOCl), 10% bromelain, 10% papain and 10% panzyme on root surface topography and microhardness of avulsed teeth. Materials and Methods: Forty healthy premolars were freshly extracted and randomly allocated into five treatment groups based on the surface agent employed; Group 1: 50 ml saline, Group 2:20 ml of 5.25% NaOCl, Group 3: 20 ml of 10% bromelain enzyme, Group 4: 20 ml of 10% papain enzyme, and Group 5: 20 ml of 10% mixed panzyme enzyme. The specimens were then subjected to confocal laser scanning microscopy and scanning electron microscopic examination. Supplemental set of freshly extracted forty premolars were decoronated longitudinally and one-half from each specimen was submitted for Vickers microhardness testing before and after application of the above-mentioned agents. Statistical Analysis: Intragroup comparison of mean percentage hardness reduction was assessed using paired t-test. Results: Treatment with NaOCl led to complete removal of PDL fibers with the presence of cracks and crazes on the root surface along with a significant reduction in microhardness. Bromelain and papain revealed regular and even distribution, while few PDL fibers were evident with papain. Panzyme revealed a shiny surface with minute cracks and a significant reduction in microhardness. Conclusion: Ten percentage bromelain for 10 min was effective in the removal of necrotic PDL fibers and preserved the cementum integrity better.

Experimental Investigation on Damage Sensitive Dynamic Responses of a Reinforced Concrete Beam

Reinforced concrete structures are subjected to damage due to environmental loading and operational conditions. Early detection of damages in reinforced concrete structures is very important. However, this becomes difficult because failure at the micro level in the form of minute cracks, develops much earlier than the visual appearance of actual damages resulting out of coalesce of several such micro level damages. Vibration based damage detection techniques, particularly use of modal testing by exciting a structure dynamically and measuring resulting responses is well established in current practice. Still, real experimental investigation involving a full scale reinforced concrete structure is somewhat rare in current literature. In the present investigation, dynamic responses of a 3.3-metre long reinforced concrete beam were measured experimentally before and after damage. Damage in the form of flexural cracks was inflicted by applying quasi-static load using a universal testing machine of capacity 300 kN under the four-point bending configuration. Broadband roving impact excitation was imparted through an impact hammer and the resulting responses were picked up by a single accelerometer. The time signals of both the force and acceleration responses were Fourier transformed using a spectrum analyser to determine the frequency response functions. The modal parameters e.g. frequencies, mode shapes, modal damping factors are found out through curve fitting. The frequency response function at a particular point has also been investigated for all the load increments and gradual changes into the dynamic properties are noted. Comparison of modal parameters between the undamaged and damaged state including their curvatures indicates that they are sensitive to the crack locations. On the other hand, the differences in frequency response functions including their curvatures were sensitive to the damage intensity in turn. The current experimental investigation provides great insight into the application of vibration-based damage detection technique to reinforced concrete structures.

Fracture mechanics analysis of a closure head of a PWR reactor pressure vessel LEFM-based SIF

In this study, fracture mechanics analysis of a closure head of a PWR reactor pressure vessel has been performed under accidental conditions. For the purpose, a wide range of elliptical surface cracks starting from minute cracks to worst-case cracks was postulated at the highest stress concentration locations of the head. The analyzed accidental conditions are small break loss of coolant accident (SB-LOCA) and Rancho-Seco transient (RST). The maximum linear elastic fracture mechanics-based stress intensity factors of the worst-case crack ‘a = 0.25 th; a = 0.33 c’ under SB-LOCA and RST are 104.37 MPa√m and 137.12 MPa√m respectively, which are less than the fracture toughness value of the material i.e. 155.6 MPa√m. Hence, the accidental conditions do not threaten the structural integrity of the proposed closure head.

A computationally efficient crack detection approach based on deep learning assisted by stockwell transform and linear discriminant analysis

This paper presents SpeedyNet, a computationally efficient crack detection method. Rather than using a computationally demanding convolutional neural network (CNN), this approach made use of a simple neural network with a shallow architecture augmented by a 2D Stockwell transform for feature transformation and linear discriminant analysis for feature reduction. The approach was employed to classify images with minute cracks under three simulated noisy conditions. Using time–frequency image transformation, feature conditioning and a fast deep learning-based classifier, this method performed better in terms of speed, accuracy and robustness compared to other image classifiers. The performance of SpeedyNet was compared to that of two popular pre-trained CNN models, Xception and GoogleNet, and the results demonstrated that SpeedyNet was superior in both classification accuracy and computational speed. A synthetic efficiency index was then defined for further assessment. Compared to GoogleNet and the Xception models, SpeedyNet enhanced classification efficiency at least sevenfold. Furthermore, SpeedyNet’s reliability was demonstrated by its robustness and stability when faced with network parameter and input image uncertainties including batch size, repeatability, data size and image dimensions.

A Hybrid Fuzzy based Cross Neighbor Filtering (HF-CNF) for Image Enhancement of fine and coarse powder Scanned Electron Microscopy (SEM) images

Image enhancement is one of the most critical stages towards any image processing application. The outcome of image enhancement determines the accuracy and precise nature of the overall output from the image processing under interest. This research paper has shown specific interests towards enhancement of Scanned Electron Microscopic (SEM) images which are primarily concerned with projection of fine details exist in internal details of surfaces, metals, fine powders, fibers etc. These fine details play a dominant role in detection of minute cracks, artifacts, progressing faults, texture of powders, their coarseness or fineness, internal details of fibers in forensics. However, due to the image capturing process which is through conventional camera-based models, noise tends to be a major source in degrading or blurring the underlying vital information. A cross neighbor fuzzy filter is a hybrid combination called Hybrid Fuzzy Based Cross Neighbor Filtering (HF-CNF) which is proposed in this research paper in order to minimize impulse and random noise to a great extent also to fine tune the further processing stages. The proposed method has been subjected to extensive analysis by comparison with state of art and recent benchmark methods and superior performance justified in terms of several validation metrics.

The effects of cellulose nanofibers compounded in water-based undercoat paint on the discoloration and deterioration of painted wood products

Cellulose nanofibers (CNFs) have many potentials as filler to improve the properties of the other materials. We have developed the novel paints containing CNFs, and which controlled the discoloration of wood products. To clarify the discoloration mechanism of wood panels using an undercoat paint containing CNFs, prepared by an integrated process from Cryptomeria japonica, the composites and films made of CNFs and acryl resin that was a raw material for the paints were prepared. Observation of the surface of the CNFs/acryl resin composite film by atomic force microscopy showed that the fibers and the resin were uniformly mixed. The composite film prevented light transmittance in the ultraviolet (UV) light region, as well as oxygen gas permeation. The permeability coefficient of the oxygen gas decreased to 60% with the addition of 1.5 wt% of CNFs to the acryl resin. The addition of CNFs also increased the breaking stress by approximately 1.5 times compared with the acryl resin film. Electron spin resonance (ESR) analysis after UV irradiation resulted in the lowest radical formation of a piece of wood wrapped in the CNFs/acryl resin composite compared with the acryl-coated specimen and the wood as it was. Therefore, the CNFs composite film shielded the UV rays and oxygen more effectively than the original acryl resin, making it difficult for these factors to reach the wood’s surface, and thus, perhaps suppressing the generation of radicals from the wood. These actions would suppress the production of coloring substances caused by the radicals, resulting in the suppression of discoloration. Furthermore, the increase in the film’s strength by the addition of CNFs would have enhanced the stability of overall the paints with a CNF-containing undercoat. These effects might have contributed not only to the prevention of discoloration but also to the prevention of the occurrence of minute cracks caused by various weather deterioration factors.

High temperature impact on calcined clay-limestone cement concrete (LC3)

A lot of CO2 is released into the atmosphere during the manufacturing process of cement, which causes a global warming problem. Calcined clay-limestone cement concrete (LC3) can be used to partially solve this problem. Limestone cement concrete is produced from calcined clay-limestone cement which is an advanced ternary mixed cement formed by the combination of 30 percent low-grade calcined clay, 15 percent limestone powder, and 5 percent gypsum and 50 percent cement clinkers. That means 50 percent of cement clinkers are to be replaced by additional cementitious materials which are beneficial for reducing CO2 emission at the time of production of cement. In the present study, calcined clay-limestone cement is used to prepared concrete and compare it with concrete using ordinary portland cement (OPC) of grade 53. The physical and chemical characteristics of prepared cement samples were carried out and compared with OPC. M30 grade of concrete was prepared by calcined clay-limestone cement; mechanical properties such as compressive strength (CS) test are carried out on prepared concrete. After the age of 28 days, M30 grade of concrete was exposed to 100 °C, 200 °C, 400 °C, 600 °C, and 800 °C temperature, surface texture, weight loss, compressive strength test were carried on the cubes of size 150 × 150 × 150 mm3. The SEM analyses were carried out over 100 °C and 600 °C temperature on OPC and calcined clay-limestone cement concrete. The result shows that the compressive strength reduces with an increase in exposed temperature. The compressive strength decreases after 200 °C and significant losses occur after 400 °C. When the temperature reached 400 °C, noticeable minute cracks started to appear on the surface of the cube specimens.

Absorption and Strength Properties of Short Carbon Fiber Reinforced Mortar Composite

This paper presents the water absorption and strength properties of short carbon fiber reinforced mortar (CFRM) composite. Four CFRM composites with 1%, 2%, 3%, and 4% short pitch-based carbon fibers were produced in this study. Normal Portland cement mortar (NCPM) was also prepared for use as the control mortar. The freshly mixed mortar composites were tested for workability, wet density, and entrapped air content. In addition, the hardened mortar composites were examined for compressive strength, splitting tensile strength, flexural strength, and water absorption at the ages of 7 and 28 days. The effects of different carbon fiber contents on the tested properties were observed. Test results showed that the incorporation of carbon fibers decreased the workability and wet density, but increased the entrapped air content in mortar composite. Most interestingly, the compressive strength of CFRM composite increased up to 3% carbon fiber content and then it declined significantly for 4% fiber content, depending on the workability and compaction of the mortar. In contrast, the splitting tensile strength and flexural strength of the CFRM composite increased for all fiber contents due to the greater cracking resistance and improved bond strength of the carbon fibers in the mortar. The presence of short pitch-based carbon fibers significantly strengthened the mortar by bridging the microcracks, resisting the propagation of these minute cracks, and impeding the growth of macrocracks. Furthermore, the water absorption of CFRM composite decreased up to 3% carbon fiber content and then it increased substantially for 4% fiber content, depending on the entrapped air content of the mortar. The overall test results suggest that the mortar with 3% carbon fibers is the optimum CFRM composite based on the tested properties.

Effect of water spray on degradation of styrene-butadiene-rubber during accelerated weathering tests

Accelerated weathering tests using a xenon lamp were performed on styrene-butadiene rubber (SBR) under two conditions: only photo irradiation (photo-irradiated condition) and the addition of intermittent water spraying to photo irradiation (photo-irradiated/water-sprayed condition). Degradation mechanisms under these conditions were evaluated based on changes in chemical structure, hardness, and morphology of the exposed surface during weathering tests. The morphology of the exposed surfaces differed significantly between the two weathering conditions. Random minute cracks, known as crazes, were clearly observed under the photo-irradiated/water-sprayed condition. To clarify the origin of such craze propagation, the temperature change accompanying water spraying was traced. A combination of temperature decrease during water spraying and subsequent increase due to water evaporation was repeated under the photo-irradiated/water-sprayed condition. Such periodic temperature change caused the sample to expand and contract; however, the exposed surface could not follow this dimensional change, resulting in craze. This result indicates that water spraying is a degradation factor for accelerated weathering tests on SBR, especially change of surface shape.

Fluorescence microscopy tracking of dyes, nanoparticles and quantum dots during growth of polymer spherulites

The distribution of additives and nanoparticles in a semicrystalline polymer is largely dependent on the complex hierarchical polymer morphology and the kinetics of its development. Here we show by in-situ fluorescence microscopy (FM), coupled with polarized optical and scanning electron microscopy, that a substantial fraction of the additive (Nile Red, NR) and even NR-labelled silica nanoparticles (NP) and quantum dots (QD) was pushed ahead of the growing spherulites during melt-crystallization. For the 35 and 200 nm NPs this was unexpected because their diffusion coefficient based on Stokes-Einstein equation should have been 2–3 orders of magnitude slower than the rate at which spherulites were growing. Another surprising finding was that much of the initially rejected NR and some QDs subsequently re-entered the spherulites through back-diffusion, posing the question why they were then rejected in the first place. The excessive initial rejection of NR and QDs and the unexpectedly rapid migration of NPs are both explained by the additive preferentially filling and being carried along by the polymer depletion zone in the melt ahead of the growing spherulite, and the high negative pressure in these zones. The effectiveness of FM in detecting minute cracks and cavities is also demonstrated. The results also show that the most severe clustering of additives occurs where spherulites did not nucleate, a problem preventable by the addition of nucleating agent.

Analysis of Al-SiCp nano composite and study of its machining process by using coated carbide tool

The present study deals with aluminium and silicon carbide (Al-SiCp) metal matrix nano composite material. In this process, silicon carbide nano particles of weight fraction 1%, 1.5% and 2% weight are mixed with aluminium molten metal. Optical microscopy study is conducted for all the samples and it is found that there is some formation of minute cracks only for 2 wt% sample which might be due to the generation of high heat and temperature. Later, the machining of Al-SiCp workpiece has been carried out by CNC lathe using coated carbide insert. The design of experiment has been obtained by Taguchi L16 orthogonal array at three different factors (feed, speed and depth of cut) at four different levels. The response parameters i.e. flank wear of coated carbide tool and surface roughness of the Al-SiCp workpiece has been optimized by using Principal Component Analysis. After the machining operation, heat affected zone, tool wear, burr and damaged zone of the tool can be observed under Scanning Electron Microscope. Analysis of Variance confirms feed, depth of cut and cutting speed to be the most significant parameters affecting the Multiple Performance Index.

Activity concentrations of 238U and 226Ra in two European black shales and their experimentally-derived leachates

The production of gas from unconventional resources became an important position in the world energy economics. In 2012, the European Commission's Joint Research Centre estimate 16 trillion cubic meters (Tcm) of technically recoverable shale gas in Europe. Taking into account that the exploitation of unconventional gas can be accompanied by serious health risks due to the release of toxic chemical components and natural occurring radionuclides into the return flow water and their near-surface accumulation in secondary precipitates, we investigated the release of U, Th and Ra from black shales by interaction with drilling fluids containing additives that are commonly employed for shale gas exploitation.We performed leaching tests at elevated temperatures and pressures with an Alum black shale from Bornholm, Denmark and a Posidonia black shale from Lower Saxony, Germany. The Alum shale is a carbonate free black shale with pyrite and barite, containing 74.4 μg/g U. The Posidonia shales is a calcareous shale with pyrite but without detectable amounts of barite containing 3.6 μg/g U.Pyrite oxidized during the tests forming sulfuric acid which lowered the pH on values between 2 and 3 of the extraction fluid from the Alum shale favoring a release of U from the Alum shale to the fluid during the short-term and in the beginning of the long-term experiments. The activity concentration of 238U is as high as 23.9 mBq/ml in the fluid for those experiments. The release of U and Th into the fluid is almost independent of pressure. The amount of uranium in the European shales is similar to that of the Marcellus Shale in the United States but the daughter product of 238U, the 226Ra activity concentrations in the experimentally derived leachates from the European shales are quite low in comparison to that found in industrially derived flowback fluids from the Marcellus shale. This difference could mainly be due to missing Cl in the reaction fluid used in our experiments and a lower fluid to solid ratio in the industrial plays than in the experiments due to subsequent fracking and minute cracks from which Ra can easily be released.

Changes in Some Mechanical and Physical Properties and Anatomical Structure of Spruce and Larch Wood after Fire-Retardant Treatment

Changes in the physical and mechanical properties and anatomical structures of spruce (Picea) and larch (Larix) specimens before and after fire-retardant impregnation were studied. Results indicated that the static modulus of elasticity (MOE), dynamic modulus of elasticity (DMOE), and the Brinell hardness of the specimens decreased for both wood species upon post-treatment. This could be accounted for by the degradation of hemicelluloses by the phosphorus-based compound, the minute cracks in the latewood cell wall, and the enlarged width of the cell lumen of the specimen resulting from the vacuum-pressure treatment. However, the decreased ratio of the MOR and DMOE to density contributed to lower sound transmission, which is expected to be important in a housing environment.

Assessment of surface relief and short cracks under cyclic creep in a type 316LN austenitic stainless steel

Formation of surface relief and short cracks under cyclic creep (stress-controlled fatigue) in type 316LN stainless steel was studied at temperatures ranging from ambient to 923 K using scanning electron microscopy technique. The surface topography and crack distribution behaviour under cyclic creep were found to be strong functions of testing temperature due to the difference in strain accumulation. At 823 K, surface relief mainly consisted of fine slip markings due to negligible accumulation of strain as a consequence of dynamic strain ageing (DSA) which led to an increase in the cyclic life. Persistent slip markings (PSM) with distinct extrusions containing minute cracks were seen to prevail in the temperature range 873–923 K, indicating a higher slip activity causing higher strain accumulation in the absence of DSA. Besides, a large number of secondary cracks (both transgranular and intergranular) which were partially accentuated by severe oxidation, were observed. Extensive cavitation-induced grain boundary cracking took place at 923 K, which coalesced with PSM-induced transgranular cracks resulting in failure dominated by creep that in turn led to a drastic reduction in cyclic life. Investigations on the influence of stress rate were also carried out which underlined the presence of DSA at 823 K. At 923 K, lowering the stress rate caused further strengthening of the contribution from creep damage marked by a shift in the damage mechanism from cyclic slip to diffusion.

Research on the Multi-Actuator and Sensor Detecting Technology Based on Piezoelectric Composite Materials

Traditional ultrasonic methods are popular in identifying easily detectable cracks, but are not good enough in minute crack detection. Early damage identification is important in preventing larger crack development and future catastrophes. Highly sensitive and precise actuator/sensor is employed to improve the detection capability of these minute cracks. The Orthotropic Piezoelectric Composite Material (OPCM) has been developed as a functional material that can be conveniently used as a highly sensitive actuator/sensor. Comparing the OPCM with the traditional elements, the former has the ability of exciting and receiving focus power and directional strain waves. They have been used in non-destructive technology in many structural engineering inspections. Using the filtering capabilities of the OPCM sensor and Hilbert-Huang Transform (HHT) method, the experimental results show that by using the multi-actuator and sensor, the simulated cracks inside aluminum plane specimen can be successfully identified.

Physical and tensile properties of chemically modified wheat straw/poly lactic acid composites

In the present study poly lactic acid (PLA) and wheat straw fibers are used to make biocomposites. For a better compatibility between the two phases, wheat straw fibers were treated by silane and acetylation. Twin screw extruder was used to mix the substances, and compression molding was used to produce standard samples. Physical properties testing including water absorption and thickness swelling were studied to analyze the composites produced. Order to analyze changes occurred in samples after their immersion in water for 1,440 hours, pictures were made from the surfaces of the samples, using SEM. Results of water absorption and thickness swelling showed that the use of acetylated fibers in PLA composites resulted in the least water absorption and thickness swelling. SEM pictures showed that composites of PLA/ acetylated wheat straw fibers did not indicate a certain change after 1,440 hours of immersion in water. While composites of PLA/ untreated fibers showed noticeable gaps and cracks on the surfaces of the samples, PLA composites treated with silane showed only minute cracks on the surface of the sample. Analysis of tensile properties indicated that the tensile modulus of composites of PLA/ treated fibers showed a meaningful increase compared to pure PLA. The highest level of tensile properties was recorded for composites of PLA/ fibers treated with silane.