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1.
Semin Vasc Surg ; 37(1): 3-11, 2024 Mar.
Artículo en Inglés | MEDLINE | ID: mdl-38704181

RESUMEN

The diagnosis and clinical features of thoracic outlet syndrome have long confounded clinicians, owing to heterogeneity in symptom presentation and many overlapping competing diagnoses that are "more common." Despite the advent and prevalence of high-resolution imaging, along with the increasing awareness of the syndrome itself, misdiagnoses and untimely diagnoses can result in significant patient morbidity. The authors aimed to summarize the current concepts in the clinical features and diagnosis of thoracic outlet syndrome.


Asunto(s)
Valor Predictivo de las Pruebas , Síndrome del Desfiladero Torácico , Síndrome del Desfiladero Torácico/diagnóstico , Síndrome del Desfiladero Torácico/terapia , Síndrome del Desfiladero Torácico/fisiopatología , Síndrome del Desfiladero Torácico/diagnóstico por imagen , Humanos , Factores de Riesgo , Pronóstico , Diagnóstico Diferencial , Diagnóstico por Imagen/métodos , Errores Diagnósticos
2.
Phys Ther ; 104(6)2024 Jun 04.
Artículo en Inglés | MEDLINE | ID: mdl-38501862

RESUMEN

OBJECTIVE: Clinical practice guidelines recommend the radial nerve mechanosensitivity evaluation in patients with lateral epicondylalgia. Despite different positions and sequences having been described, no research analyzed how each variation triggers symptoms associated with lateral epicondylalgia. The aim of this study was to explore the effects of different positions and sequences in the upper limb neural tension test 2b (ULNT2b) in symptom responses in patients with lateral epicondylalgia. METHODS: In this observational study, 66 patients underwent 4 test conditions: standard ULNT2b, ULNT2b proximal to distal, ULNT2B with resisted supination, and resisted supination isolated. Paresthesia sensations, symptom reproduction, pain intensity (measured using a visual analog scale), and distribution of painful symptoms data were collected. RESULTS: Significant differences in paresthesia sensations were observed between groups, with significant differences between the standard ULNT2B and other ULNT variations or resisted supination maneuvers. Symptom reproduction also differed significantly across groups, with significant differences between the standard ULNT2B and other ULNT or resisted supination tests. The positive/negative test and percentage of distribution of painful symptoms scores varied significantly across 4 conditions in both lateral and frontal views. Although pain intensity scores during tests were comparable among the tests, distribution of painful symptoms differed significantly. CONCLUSION: Variations in the ULNT2b test can affect symptom responses in patients with lateral epicondylalgia. The standard ULNT2b test appears more effective at reproducing symptoms, intensity of paresthesia, and distribution of painful symptoms compared to other ULNT variations and the resisted supination test. IMPACT: ULNT2b sequences have been shown to elicit varying responses concerning paresthesia, replication of familiar symptoms, positive/negative test results, and distribution of painful symptoms. Clinicians should consider specific test variations during the patients' radial nerve mechanosensitivity assessment to identify aggravating factors reproducing recognizable symptoms. A control group of asymptomatic participants and the role of presence of other comorbidities, psychological factors, or the duration of symptoms were not considered in this study and might play an important role influencing the results of the tests.


Asunto(s)
Dimensión del Dolor , Parestesia , Nervio Radial , Codo de Tenista , Humanos , Masculino , Femenino , Codo de Tenista/fisiopatología , Persona de Mediana Edad , Nervio Radial/fisiopatología , Adulto , Parestesia/fisiopatología , Parestesia/etiología , Supinación/fisiología , Extremidad Superior/fisiopatología
3.
Materials (Basel) ; 17(2)2024 Jan 05.
Artículo en Inglés | MEDLINE | ID: mdl-38255444

RESUMEN

The effectiveness of a ductile fracture model in accurately predicting fracture initiation has been demonstrated. In this study, we concentrate on applying the ductile fracture model to pre-cracked structures constructed from SUS304L stainless steel with experimental and numerical analyses. The Swift hardening law was employed to extend the plastic behavior beyond the onset of necking. Additionally, the Hosford-Coulomb model, integrated with a damaged framework, was utilized to predict ductile fracture behavior, particularly under non-proportional loading conditions. Tension tests were conducted on various specimens designed to illustrate various fracture modes resulting from geometric effects. Numerical analyses were conducted to explore the loading histories, utilizing an optimization process to calibrate fracture model parameters. The proposed fracture model is validated against pre-cracked structures detailed in a reference paper. The results convincingly demonstrate that the fracture model effectively predicts both fracture initiation and propagation in pre-cracked structures.

4.
Braz J Phys Ther ; 27(6): 100558, 2023.
Artículo en Inglés | MEDLINE | ID: mdl-37967500

RESUMEN

BACKGROUND: The validity of the ULTT is unclear, due to heterogeneity of test procedures and variability in the definition of a positive test OBJECTIVE: To evaluate test procedures and positive diagnostic criteria for the upper limb tension test (ULTT) in diagnostic test accuracy studies. METHODS: A systematic review of diagnostic accuracy studies was performed. We conducted a search of the DiTA (Diagnostic Test Accuracy) database and selected primary studies evaluating the diagnostic accuracy of the ULTT. We assessed risk of bias, performed data extraction on study characteristics, test procedures, and positive diagnostic criteria, and performed a descriptive analysis. RESULTS: We included nine studies (681 participants), four diagnosing people with cervical radiculopathy (CR), four diagnosing people with carpal tunnel syndrome (CTS), and one included both CR and CTS. The risk of bias varied between 2 and 6 out of 6 positive items. Eight studies reported on the ULTT1 (median nerve). Overall, all studies clearly described their test procedures and positive diagnostic criteria although the order of movements and the diagnostic criteria between studies varied. We suggest a more standardised test procedure for the ULTT1 to consist of: 1) stabilising the shoulder in abduction, 2) extending the wrist/fingers, 3) supinating the forearm, 4) externally rotating the shoulder, 5) extending the elbow, and finally 6) performed structural differentiation by side bending (lateral flexion) of the neck. This proposed test procedure should reproduce the symptoms and enables the clinician to evaluate whether symptoms increase/decrease when stressing or relaxing the nerves. CONCLUSION: Based on our findings we proposed a more standardised test procedure for the ULTT1 with accompanying positive diagnostic criteria to facilitate homogeneity in future diagnostic accuracy studies of the ULTT.


Asunto(s)
Síndrome del Túnel Carpiano , Examen Físico , Humanos , Extremidad Superior/fisiología , Muñeca , Síndrome del Túnel Carpiano/diagnóstico , Dedos
5.
Acta Biomater ; 162: 304-311, 2023 05.
Artículo en Inglés | MEDLINE | ID: mdl-36963595

RESUMEN

The fibers of the deep-sea sponge Euplectella aspergillum exhibit exceptional mechanical properties due to their unique layered structure at a micrometer length scale. In the present study, we utilize a correlative approach comprising of in situ tensile testing inside a scanning electron microscope (SEM) and post-failure fractography to precisely understand mechanisms through which layered architecture of fibers fracture and improves damage tolerance in tensile loading condition. The real-time observation of fibers in the present study confirms for the first time that the failure starts from the surface of fibers and proceeds to the center through successive layers. The concentric layers surrounding the central core sacrifice themselves and protect the central core through various toughening mechanisms like crack deflection, crack arrest, interface debonding, and fiber pullout. STATEMENT OF SIGNIFICANCE: Biological materials often exhibit multiscale hierarchical structures that can be incorporated into the design of next generation of engineering materials. The fibers of deep-sea sponge E. aspergillum possess core-shell like layered architecture. Our in situ study reveals astounding strategies by which this architecture delays the fracture of the fiber. The core-shell architecture of these fibers behaves like fiber-reinforced ceramic matrix composite, where the outer shells act as a matrix and the central core acts as a fiber. The outer shells take the environmental brunt and scarify themselves to protect the central core. The precise understanding of damage evolution presented here will help to design architected materials for load-bearing applications.


Asunto(s)
Poríferos , Dióxido de Silicio , Poríferos/química
6.
Materials (Basel) ; 16(3)2023 Jan 31.
Artículo en Inglés | MEDLINE | ID: mdl-36770208

RESUMEN

In this work, roof felts are considered. Special attention is paid to the mechanical properties and self-healing (SH) phenomena under elevated temperatures. The results of the heating and strength tests for the entire range of material work, from the first load to sample breaking, are shown with respect to the angle of reinforcement relative to the longitudinal axis of the sample and different ways of breaking the continuity of the material. The influence that the material thickness and modifiers used for the production of the base material have on the obtained results was also pointed out. The meaningful SH strength is reported-from 5% up to 20% of the strength of the undamaged material-which, in perspective, can provide comprehensive knowledge of the optimal use of roofing felts and its proper mathematical modeling.

7.
Asian Pac J Cancer Prev ; 23(10): 3355-3360, 2022 Oct 01.
Artículo en Inglés | MEDLINE | ID: mdl-36308359

RESUMEN

BACKGROUND: Lymphedema in breast cancer survivors is a very common condition which progressively may lead to entrapment  neuropathy. In lymphedema there is accumulation of fluid due to removal of lymph nodes which causes stretching of nerve fibres within the skin, compression on top of the nerve bundle leading to nerve entrapment. This will increase the neural mechanosensitivity and functional impairment of shoulder as a protective neural response to movement or traction. METHODS: This study was carried out by assessing the total 72 breast cancer survivor women, with lymphedema. Out of 72, 28 of women underwent lumpectomy, 12 underwent quadrantectomy and 32 underwent unilateral mastectomy.  These subjects were assessed for neural tissue mobility by taking pain assessment using visual analogue scale (VAS), range of motion (ROM) using goniometer, lymphedema measurement using an inch tape. The neural tissue mobility for  median nerve, ulnar nerve and radial nerve was measured using limb tension test. RESULT: The result obtained from this study showed that neural tissue mobility was significantly impaired in breast cancer survivors with lymphedema. The result of the upper limb tension tests showed 32 women with mild lymphedema had median nerve affected on the involved side 54.1%, about  21 women had moderate lymphedema with 75% of women had median and 25% ulnar nerve affected with median nerve affected in majority of women. Only 19 women with severe lymphedema had all the three nerves affected. CONCLUSION: This study of women who have undergone surgical intervention for breast cancer concludes that there was significant amount of neural tissue impairment noted to mechanical provocation test post operatively after 6 months of surgery. The study suggests that severity of lymphedema was directly related to the nerves affected due to neural tissue impairment.


Asunto(s)
Neoplasias de la Mama , Supervivientes de Cáncer , Linfedema , Femenino , Humanos , Neoplasias de la Mama/complicaciones , Neoplasias de la Mama/cirugía , Neoplasias de la Mama/patología , Mastectomía/efectos adversos , Linfedema/etiología , Sobrevivientes , Extremidad Superior/patología
8.
J Pers Med ; 12(10)2022 Sep 28.
Artículo en Inglés | MEDLINE | ID: mdl-36294740

RESUMEN

Hypertension, as a primary risk factor for many fatal disorders, is prevalent in the elderly. There is wide literature on hypertension dealing with its biological and/or biochemical aspects; however, limited research is available on the multifactorial nature of hypertension from a mechanobiological standpoint. This study intended to study in parallel histopathological alterations and deviated protein expressions with the mechanical behavior of the hypertensive tissues. The Goldblatt (2K1C) method was chosen for induction of renovascular hypertension in rabbits. The microstructural and immunohistological characteristics of the aortic, pancreatic, and brain vasculature were investigated. The mechanical properties of the aortic tissue were also evaluated using biaxial tensile tests. Our findings indicated severe hypertrophy of the hypertensive vessels and declined content of intact smooth muscle cells. Most of the collagen I content of the wall was compromised and less functional type III collagen was highly expressed. Reversed collagen I to collagen III ratio was the main contributor to the hypertrophic and less stiff hypertensive vessel walls. The multifactorial nature of hypertension is illustrated, and smooth muscle cell detachment is identified as the sign of described degenerative cascades all along the arterial tree.

9.
Materials (Basel) ; 15(14)2022 Jul 17.
Artículo en Inglés | MEDLINE | ID: mdl-35888444

RESUMEN

Mode I fracture (tensile type) is the common cracking mode of asphalt pavements, which is caused by thermal cyclic loading or traffic. Some studies allow the analysis of the fracture modes by means of standardized tests, some of which are limited, difficult, with little repeatability or do not generate an adequate tension state. In this paper, mode I fracture toughness of asphalt mixtures with symmetric geometry specimens at intermediate temperature is evaluated. Experimental results from direct tension test and simulations on asphalt mix specimens subjected to intermediate temperatures of 10, 20 and 30 °C, mode I load rates (0.5, 1 and 2 mm/min) and notches (2 and 3 cm) were compared to find the variables that reflect the operating conditions of the asphalt mix. Results showed that shear stresses are 8.12% lower in the simulations with respect to the tests, while the load-deformation curves show 30% and 35% variation, where the temperature of 20 °C, the notch of 2 cm and the loading speed of 1 mm/min are the conditions that best represent the stress state of the test; moreover, it manages to consider the elastic and viscous components of the material.

10.
Materials (Basel) ; 15(12)2022 Jun 12.
Artículo en Inglés | MEDLINE | ID: mdl-35744222

RESUMEN

Aramid and polyamide cords are used in a wide range of applications, particularly in the automotive industry (tire reinforcement) and textile industry for military and fireguard purposes. The problem of the reliable experimental study of tensile behavior of synthetic cords is considered in this paper. In the available standards for synthetic cord testing, particularly ASTM D 885-03, the tensile test must result with the cord damage in the middle of gauge length, and the cords should be fixed in the machine clamps. The trial test gave damage near the clamps. We propose a novel testing stage mounted in the testing machine clamps to achieve the uniform tensile stress distribution in the gauge length of the measured cords. The results of the deformations were measured in two ways: using testing machine head displacement and a videoextensometer. Stress curves of four distinguished cords were evaluated and compared. The second method allowed to acquire results differing from the manufacturers' data from 0.7% to 21.5%, which allowed for the conclusion that the designed test stand allows for obtaining reliable results for stretched cords.

11.
J Indian Soc Periodontol ; 26(2): 162-168, 2022.
Artículo en Inglés | MEDLINE | ID: mdl-35321301

RESUMEN

Context: The mucogingival junction (MGJ) is one of the important anatomical entities which mark the apical termination of attached gingiva, except that at palatal side. Its position is genetically determined like other organs and tissues in our body. There are certain anatomic aberrations such as abnormal teeth eruption or high frenal attachments and pathologies, such as periodontitis, leading to its absence. There are no studies on the prevalence of teeth having no clinically detectable MGJ. There is a resurgence of importance of attached gingiva, reflected by the definite presence of MGJ, through the field of dental implantology. Aims: We aim to evaluate the prevalence of teeth without clinically detectable MGJ on the buccal aspect of dentate alveolar processes. Settings and Design: This cross-sectional observational clinical study was conducted in the department of periodontology which was approved by the institutional ethical committee. Materials and Methods: Periodontally healthy as well as diseased patients of age 18-50 years were included in the study. The detection of MGJ was carried out by visual method, tension test, rolling probe method, and Lugol's iodine solution, and confirmation from any two methods was considered for the absence of MGJ. The etiology of MGJ absence (gingival recession, pocket till MGJ, trauma, abnormal frenal attachment, malposition of tooth, abnormal habits, severe abrasion, etc.,) was also evaluated. Statistical Analysis Used: Simple statistics in the form of averages and percentages were used for calculations. Results: A total of 130 subjects (3637 teeth) were examined out of which 32 (24.6%) subjects showed no clinically detectable MGJ. In all subjects, on an average, every subject has 28 teeth and out of the total 3637 teeth analyzed, only 91 (2.5%) teeth were without detectable MGJ. Conclusion: Almost 25% of the population may show a tooth or few teeth without a clinically detectable MGJ. The prevalence of teeth without clinically detectable MGJ per mouth is very low at 0.7 (approximately 1 tooth/subject).

12.
São José dos Campos; s.n; 2022. 46 p. tab, ilus.
Tesis en Portugués | BBO - Odontología | ID: biblio-1397775

RESUMEN

O objetivo do presente estudo in vitro é investigar possíveis alterações nas propriedades mecânicas de alinhadores transparentes de poliuretano (PU). Em um estudo piloto, amostras de alinhadores foram submetidas à Espectroscopia Raman antes e depois de irradiações de UV e de LED, e os resultados demonstraram evidente alteração da estrutura molecular. Em virtude disso, foi levantada a hipótese de que as radiações também provoquem alterações nas propriedades mecânicas. Foram confeccionados trinta alinhadores, pela empresa Align Technology Inc. (Invisalign ®), distribuídos em três grupos de dez alinhadores cada. Um grupo controle não sofreu irradiação, e os outros dois grupos foram irradiados: um com radiação UV dentro de uma câmara construída para esse tipo de experimento e um terceiro grupo com radiação LED por fotopolimerizador específico. Os grupos foram definidos, as irradiações foram efetuadas sob sigilo por um operador e as identificações, armazenadas em envelopes lacrados, somente foram reveladas após a conclusão dos testes e tabulação dos dados obtidos. Para avaliação das propriedades mecânicas, neste caso resistência à deformação, utilizou-se uma máquina de ensaio universal para o teste de carga. Os alinhadores foram preenchidos com gesso, com um alívio que deixou livres as áreas a serem testadas. O teste de tensão mostrou que tendo como referência o grupo controle, os alinhadores submetidos à radiação UV tornaram-se menos rígidos e os submetidos à radiação LED tornaram-se mais rígidos. O teste de H de Kruskal-Wallis foi realizado e evidenciou não haver diferença estatisticamente significativa na carga aplicada nas amostras dos diferentes grupos. O mesmo teste foi utilizado para avaliar a diferença entre a deformação ocorrida e o módulo de elasticidade nos três grupos. A hipótese nula foi rejeitada em ambos os testes, considerando o nível de 5% de significância, o que assegura que há uma diferença significativa entre os três grupos quanto à irradiação de UV ou LED. Ainda assim, para uma avaliação mais minuciosa utilizou-se o teste de Mann-Whtiney comparando os grupos dois a dois. O resultado apontou que as irradiações aplicadas neste estudo são responsáveis pelas diferenças estatísticas apresentadas. (AU)


The aim of the present in vitro study is to investigate possible changes in the mechanical properties of transparent polyurethane (PU) aligners. In a pilot study, specimens of aligners were subjected to Raman Spectroscopy before and after UV and LED irradiation, and the results showed evident alteration of the molecular structure. Because of this, it was hypothesized that the radiations also cause changes in the mechanical properties. Thirty aligners were made by Align Technology Inc. (Invisalign®), distributed in three groups of ten aligners each. A control group was not irradiated, and the other two groups were irradiated: one with UV radiation inside a chamber built for this type of experiment, and the third group with LED radiation by a specific photopolymerizer. The groups were defined, the irradiations were done under confidentiality by an operator and the identifications, stored in sealed envelopes, were only revealed after the completion of the tests and tabulation of the data obtained. To evaluate the mechanical properties, in this case resistance to deformation, a universal testing machine was used for the load test. The aligners were filled with plaster, with a relief that left free the areas to be tested. The tension test showed that taking the control group as reference, the aligners submitted to UV radiation became less rigid and those submitted to LED radiation became more rigid. The Kruskal-Wallis H test was performed and showed that there was no statistically significant difference in the load applied to the samples of the different groups. The same test was used to evaluate the difference between the deformation occurred and the modulus of elasticity in the three groups. The null hypothesis was rejected in both tests, considering the 5% significance level, which ensures that there is a significant difference between the three groups regarding UV or LED irradiation. Even so, for a more detailed evaluation the Mann-Whtiney test was used, comparing the groups two by two. The result pointed out that the irradiations applied in this study are responsible for the statistical differences presented (AU)


Asunto(s)
Aparatos Ortodóncicos Removibles , Poliuretanos , Espectrometría Raman , Radiación , Rayos Ultravioleta , Pruebas Mecánicas
13.
Entramado ; 17(1): 290-301, ene.-jun. 2021. tab, graf
Artículo en Español | LILACS-Express | LILACS | ID: biblio-1249790

RESUMEN

RESUMEN Obtener la envolvente de ruptura de suelos no saturados requiere de equipos especializados, de elevado costo y difícil acceso. Sin embargo, a través de ensayos de laboratorio simples combinados como corte directo, tracción indirecta y succión, es posible determinar la envolvente. La presente investigación busca, por tanto, validar dicha metodología, en un material limo de origen residual de la ciudad de Medellín-Antioquia, Colombia, compactado a la máxima densidad a través del ensayo Proctor normal. La validación se efectúa por medio de la repetitividad de una serie de ensayos de corte directo para diferentes valores de succión; comprobando que, es posible encontrar la envolvente de ruptura al corte de un suelo fino residual compactado, para distintas condiciones de succión, por medio de los ensayos de laboratorio de corte directo en condición consolidada y drenada, succión por el método del papel filtro y tracción indirecta, cuando no se cuenta con equipos de corte con succión controlada.


ABSTRACT Obtaining the failure envelope of unsaturated soils requires specialized equipment, which is expensive and difficult to access. Nevertheless, by combining simple laboratory tests like direct shear test on saturated samples, indirect tension test, and soil suction measurements by filter paper it is also possible to determine the envelope. This research aims to validate this latter methodology on a residual origin silt material from the city of Medellin, Colombia, which is compacted to the maximum dry density through the standard proctor test. The validation is carried out by repeating a series of direct shear tests for different suction values. It was verified that it is possible to find the shear failure envelope of a compacted fine-grained residual soil for different suction conditions, using the direct shear test under consolidated drained conditions, suction by the filter paper method, and the indirect tension test, when no suction controlled shear equipment is available.


RESUMO A obtenção da envoltória de ruptura de solos não saturados com controle de sucção requer equipamentos especiais, que são caros e de difícil acesso. No entanto, através de ensaios simples laboratoriais combinados, tais como os de cisalhamento direto, tração indireta e sucção, é possível determinar a envoltória de resistência. A presente investigação procura validar esta metodologia, usando um material siltoso de origem residual da cidade de Medellin-Antioquia, Colômbia, compactado na condição de densidade máxima obtida no ensaio de compactação Proctor normal. A validação é feita por meio da realização de uma série de ensaios de cisalhamento direto para diferentes valores de sucção; mostrando que é possível encontrar a envoltória de ruptura de um solo fino residual compactado, para diferentes condições de sucção, por meio de ensaios laboratoriais de cisalhamento direto consolidados drenados, sucção determinada pelo método do papel de filtro e ensaio de tração indireta, quando não se dispõe de equipamento de cisalhamento direto à sucção controlada.

14.
Materials (Basel) ; 14(3)2021 Jan 28.
Artículo en Inglés | MEDLINE | ID: mdl-33525439

RESUMEN

The tensile properties of plain concrete are very important for the concrete structural design, and the complete tensile stress-strain curve is essential for creating accurate and reliable designs, especially when considering special load cases such as earthquakes and impacts. To study the complete tensile stress-deformation response of plain concrete, the direct tension tests were conducted on a novel thermal tensile testing machine (TTTM), which was reformed from a hydraulic universal testing machine (UTM). Acoustic emission (AE) technology was applied to monitor the damage process of plain concrete in tests. The TTTM was powered by the thermal expansion of loading columns, and had a stiffness similar to the specimen, thus eliminating the potential AE noises in the UTM, and simulating the rapid fracture process in real concrete structures. A static-dynamic acquisition system was established to obtain the complete tensile stress-strain curves, of which the data before and at the fracture moment were respectively acquired by the static acquisition system and the dynamic acquisition system. The AE technology is a useful approach to analyze the damage process of concrete, and makes it feasible to determine the damage state and the fracture location of the specimen in real time.

15.
Materials (Basel) ; 14(4)2021 Feb 05.
Artículo en Inglés | MEDLINE | ID: mdl-33562884

RESUMEN

This paper presents an experimental material campaign focusing on fiber-reinforced polymers (FRP) to be applied in a novel bridge deck panel. Laminas based on most commonly used fibers, i.e., glass, carbon, basalt and aramid, were prepared and studied in tension, shear and compression. In the subsequent test stages, different fabric reinforcements (uni- and bi-directional fabrics, woven fabrics, CSM layers) were considered for glass laminas only, and finally, a resultant laminate was designed and tested. Such an approach gives a great opportunity to create "tailor-made" laminates, as required in FRP bridge deck panels. Simultaneously with the laboratory tests, analytical calculations were performed using a few micromechanical models that aimed to determine engineering constants and strength parameters. Then, the results obtained from material testing and analytical calculations were compared, and conclusions on the compliance were drawn. Based on this validation, further analytical calculations may replace time-consuming laboratory tests and facilitate FRP deck design.

16.
Materials (Basel) ; 14(1)2021 Jan 02.
Artículo en Inglés | MEDLINE | ID: mdl-33401650

RESUMEN

Tensile performance of fiber-reinforced cementitious composite (FRCC) after first cracking is characterized by fiber-bridging stress-crack width relationships called bridging law. The bridging law can be calculated by an integral calculus of forces carried by individual fibers, considering the fiber orientation. The objective of this study was to propose a simplified model of bridging law for bundled aramid fiber, considering fiber orientation for the practical use. By using the pullout characteristic of bundled aramid fiber obtained in the previous study, the bridging laws were calculated for various cases of fiber orientation. The calculated results were expressed by a bilinear model, and each characteristic point is expressed by the function of fiber-orientation intensity. After that, uniaxial tension tests of steel reinforced aramid-FRCC prism specimens were conducted to obtain the crack-opening behavior and confirm the adaptability of the modeled bridging laws in crack-width evaluation. The experimental parameters are cross-sectional dimensions of specimens and volume fraction of fiber. The test results are compared with the theoretical curves calculated by using the modeled bridging law and show good agreements in each parameter.

17.
Scr Mater ; 422021 Jun.
Artículo en Inglés | MEDLINE | ID: mdl-38487257

RESUMEN

The elastic response of homogeneous isotropic materials is most commonly represented by their Young's modulus (E), but geometric variability associated with additive manufacturing results in materials that are neither homogeneous nor isotropic. Here we investigated methods to estimate the effective elastic modulus (Eeff) of samples fabricated by fused filament fabrication. We conducted finite element analysis (FEA) on printed samples based on material properties and CT-scanned geometries. The analysis revealed how the layer structure of a specimen altered the internal stress distribution and the resulting Eeff. We also investigated different empirical methods to estimate Eeff as guides. We envision the findings from our study can provide guidelines for modulus estimation of as-printed specimens, with the potential of applying to other extrusion-based additive manufacturing technologies.

18.
Methods Cell Biol ; 160: 327-348, 2020.
Artículo en Inglés | MEDLINE | ID: mdl-32896326

RESUMEN

Tensile testing is widely used to evaluate the mechanical properties of biological materials including soft primary plant tissues. Commercially available platforms for tensile testing are often expensive and limited in customizability. In this chapter, we provide a guide for the assembly and use of a simple and low-cost micromechanical testing apparatus suitable for research and educational purposes. The build of the setup is presented with scalability and universality in mind and is based on a do-it-yourself mind frame towards mechanical tests on plant organs and tissues. We discuss hardware and software requirements with practical details on required components, device calibration and a script to run the device. Further, we provide an example in which the device was used for the uniaxial tensile test of onion epidermis.


Asunto(s)
Botánica/instrumentación , Cebollas/fisiología , Especificidad de Órganos , Fenómenos Biomecánicos , Calibración , Epidermis de la Planta/fisiología , Análisis de Componente Principal , Programas Informáticos , Estrés Mecánico , Resistencia a la Tracción , Interfaz Usuario-Computador
19.
Ultramicroscopy ; 218: 113083, 2020 Nov.
Artículo en Inglés | MEDLINE | ID: mdl-32739752

RESUMEN

Fracturing microscale constrictions in metallic wires, such as tungsten, platinum, or platinum-iridium, is a common fabrication method used to produce atomically sharp tips for scanning tunneling microscopy (STM), field-emission microscopy and field ion microscopy. Typically, a commercial polycrystalline drawn wire is locally thinned and then fractured by means of a dislocation slip inside the constriction. We examine a special case where a dislocation-free microscale constriction is created and fractured in a single crystal tungsten rod with a long side parallel to the [100] direction. In the absence of dislocations, vacancies become the main defects in the constriction which breaks under the tensile stress of approximately 10 GPa, which is close to the theoretical fracture strength for an ideal monocrystalline tungsten. We propose that the vacancies are removed early in the tensile test by means of deformation annealing, creating a defect-free tungsten constriction which cleaves along the W(100) plane. This approach enables fabrication of new composite STM probes which demonstrate excellent stability, atomic resolution and magnetic contrast that cannot be attained using conventional methods.

20.
Materials (Basel) ; 13(12)2020 Jun 18.
Artículo en Inglés | MEDLINE | ID: mdl-32570950

RESUMEN

Tensile strength is one of the important mechanical properties of concrete, but it is difficult to measure accurately due to the brittle nature of concrete in tension. The three widely used test methods for measuring the tensile strength of concrete each have their shortcomings: the direct tension test equipment is not easy to set up, particularly for alignment, and there are no standard test specifications; the tensile strengths obtained from the test method of splitting tensile strength (American Society for Testing and Materials, ASTM C496) and that of flexural strength of concrete (ASTM C78) are significantly different from the actual tensile strength owing to mechanisms of methodologies and test setup. The objective of this research is to develop a new concrete tensile strength test method that is easy to conduct and the result is close to the direct tension strength. By applying the strut-and-tie concept and modifying the experimental design of the ASTM C78, a new concrete tensile strength test method is proposed. The test results show that the concrete tensile strength obtained by this proposed method is close to the value obtained from the direct tension test for concrete with compressive strengths from 25 to 55 MPa. It shows that this innovative test method, which is precise and easy to conduct, can be an effective alternative for tensile strength of concrete.

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