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AR Categoría: Pruebas de laboratorio
Efecto de la humedad en la tribología del revestimiento de DLC
Importance of Wear Evaluation on DLC in Humidity
Diamond-like carbon (DLC) coatings possess enhanced tribological properties, namely excellent wear resistance and a very low coefficient of friction (COF). DLC coatings impart diamond characteristics when deposited on different materials. Favorable tribo-mechanical properties make DLC coatings preferable in various industrial applications, such as aerospace parts, razor blades, metal cutting tools, bearings, motorcycle engines, and medical implants.
DLC coatings exhibit very low COF (below 0.1) against steel balls under high vacuum and dry conditions 12. However, DLC coatings are sensitive to environmental condition changes, particularly relative humidity (RH)3. Environments with high humidity and oxygen concentration may lead to significant increase in COF4. Reliable wear evaluation in controlled humidity simulates realistic environmental conditions of DLC coatings for tribological applications. Users select the best DLC coatings for target applications with proper comparison
of DLC wear behaviors exposed to different humidity.
Objetivo de medición
This study showcases the Nanovea Tribómetro equipped with a humidity controller is the ideal tool for investigating wear behavior of DLC coatings at various relative humidity.
Procedimiento de ensayo
Friction and wear resistance of DLC coatings were evaluated by the Nanovea Tribometer. Test parameters are summarized in Table 1. A humidity controller attached to the tribo-chamber precisely controlled the relative humidity (RH) with an accuracy of ±1%. Wear tracks on DLC coatings and wear scars on SiN balls were examined using an optical microscope after tests.
Note: Any solid ball material can be applied to simulate the performance of different material coupling under environmental conditions such as in lubricant or high temperature.
Resultados y debate
DLC coatings are great for tribological applications due to their low friction and superior wear resistance. The DLC coating friction exhibits humidity dependent behavior shown in Figure 2. The DLC coating shows a very low COF of ~0.05 throughout the wear test in relatively dry conditions (10% RH). The DLC coating exhibits a constant COF of ~0.1 during the test as RH increases to 30%. The initial run-in stage of COF is observed in the first 2000 revolutions when RH rises above 50%. The DLC coating shows a maximum COF of ~0.20, ~0.26 and ~0.33 in RH of 50, 70 and 90%, respectively. Following the run-in period, the DLC coating COF stays constant at ~0.11, 0.13 and 0.20 in RH of 50, 70 and 90%, respectively.
Figure 3 compares SiN ball wear scars and Figure 4 compares DLC coating wear tracks after the wear tests. The diameter of the wear scar was smaller when the DLC coating was exposed to an environment with low humidity. Transfer DLC layer accumulates on the SiN ball surface during the repetitive sliding process at the contact surface. At this stage, the DLC coating slides against its own transfer layer which acts as an efficient lubricant to facilitate the relative motion and restrain further mass loss caused by shear deformation. A transfer film is observed in the wear scar of the SiN ball in low RH environments (e.g. 10% and 30%), resulting in a decelerated wear process on the ball. This wear process reflects on the DLC coating’s wear track morphology as shown in Figure 4. The DLC coating exhibits a smaller wear track in dry environments, due to the formation of a stable DLC transfer film at the contact interface which significantly reduces friction and wear rate.
Conclusión
Humidity plays a vital role in the tribological performance of DLC coatings. The DLC coating possesses significantly enhanced wear resistance and superior low friction in dry conditions due to the formation of a stable graphitic layer transferred onto the sliding counterpart (a SiN ball in this study). The DLC coating slides against its own transfer layer, which acts as an efficient lubricant to facilitate the relative motion and restrain further mass loss caused by shear deformation. A film is not observed on the SiN ball with increasing relative humidity, leading to an increased wear rate on the SiN ball and the DLC coating.
The Nanovea Tribometer offers repeatable wear and friction testing using ISO and ASTM compliant rotative and linear modes, with optional humidity modules available in one pre- integrated system. It allows users to simulate the work environment at different humidity, providing users an ideal tool to quantitatively assess the tribological behaviors of materials under different work conditions.
Learn More about the Nanovea Tribometer and Lab Service
1 C. Donnet, Surf. Coat. Technol. 100–101 (1998) 180.
2 K. Miyoshi, B. Pohlchuck, K.W. Street, J.S. Zabinski, J.H. Sanders, A.A. Voevodin, R.L.C. Wu, Wear 225–229 (1999) 65.
3 R. Gilmore, R. Hauert, Surf. Coat. Technol. 133–134 (2000) 437.
4 R. Memming, H.J. Tolle, P.E. Wierenga, Thin Solid Coatings 143 (1986) 31
AHORA, HABLEMOS DE SU SOLICITUD
Análisis tridimensional de la superficie de una moneda con perfilometría sin contacto
Importancia de la perfilometría sin contacto para monedas
La moneda tiene un gran valor en la sociedad moderna porque se intercambia por bienes y servicios. Las monedas y billetes circulan por las manos de muchas personas. La transferencia constante de moneda física crea deformaciones en la superficie. Nanovea 3D Perfilómetro escanea la topografía de monedas acuñadas en distintos años para investigar las diferencias de superficie.
Las características de las monedas son fácilmente reconocibles para el público en general, ya que son objetos comunes. Una moneda de un céntimo es ideal para presentar la potencia del software de análisis avanzado de superficies de Nanovea: Montañas 3D. Los datos de superficie recogidos con nuestro Perfilómetro 3D permiten realizar análisis de alto nivel en geometría compleja con sustracción de superficies y extracción de contornos 2D. La sustracción de superficies con una máscara, un sello o un molde controlados compara la calidad de los procesos de fabricación, mientras que la extracción de contornos identifica las tolerancias con un análisis dimensional. El perfilómetro 3D de Nanovea y el software Mountains 3D investigan la topografía submicrónica de objetos aparentemente sencillos, como los céntimos.
Objetivo de medición
Se escaneó toda la superficie superior de cinco peniques utilizando el sensor de líneas de alta velocidad de Nanovea. El radio interior y exterior de cada penique se midió con el software de análisis avanzado Mountains. Una extracción de la superficie de cada penique en un área de interés con sustracción directa de la superficie cuantificó la deformación de la superficie.
Resultados y debate
Superficie 3D
El perfilómetro Nanovea HS2000 tardó sólo 24 segundos en escanear 4 millones de puntos en un área de 20 mm x 20 mm con un tamaño de paso de 10um x 10um para adquirir la superficie de un céntimo. A continuación se muestra un mapa de alturas y una visualización en 3D del escaneado. La vista en 3D muestra la capacidad del sensor de alta velocidad para captar pequeños detalles imperceptibles a simple vista. En la superficie de la moneda de un céntimo se aprecian muchos pequeños arañazos. Se investigan la textura y la rugosidad de la moneda vistas en la vista 3D.
Análisis dimensional
Se extrajeron los contornos del centavo y mediante un análisis dimensional se obtuvieron los diámetros interior y exterior de la característica del borde. La media del radio exterior fue de 9,500 mm ± 0,024, mientras que la media del radio interior fue de 8,960 mm ± 0,032. Otros análisis dimensionales que Mountains 3D puede realizar en fuentes de datos 2D y 3D son la medición de distancias, la altura de los escalones, la planitud y el cálculo de ángulos.
Sustracción de superficies
La figura 5 muestra el área de interés para el análisis de sustracción de superficie. El penique de 2007 se utilizó como superficie de referencia para los cuatro peniques más antiguos. La sustracción de la superficie del penique de 2007 muestra las diferencias entre los peniques con agujeros/picos. La diferencia de volumen total de la superficie se obtiene sumando los volúmenes de los agujeros/picos. El error cuadrático medio indica la concordancia entre las superficies de los céntimos.
Conclusión
El escáner de alta velocidad HS2000L de Nanovea escaneó cinco monedas de un penique acuñadas en diferentes años. El software Mountains 3D comparó las superficies de cada moneda mediante extracción de contornos, análisis dimensional y sustracción de superficies. El análisis define claramente los radios interior y exterior entre los peniques, a la vez que compara directamente las diferencias de las características superficiales. Con la capacidad del perfilómetro 3D de Nanovea para medir cualquier superficie con una resolución nanométrica, combinada con las capacidades de análisis de Mountains 3D, las posibles aplicaciones de investigación y control de calidad son infinitas.
AHORA, HABLEMOS DE SU SOLICITUD
Acabado dimensional y superficial de los tubos poliméricos
Importance of Dimensional and Surface Analysis of Polymeric Tubes
Tubes made from polymeric material are commonly used in many industries ranging from automotive, medical, electrical, and many other categories. In this study, medical catheters made of different polymeric materials were studied using the Nanovea Perfilómetro 3D sin contacto to measure surface roughness, morphology, and dimensions. Surface roughness is crucial for catheters as many problems with catheters, including infection, physical trauma, and inflammation can be linked with the catheter surface. Mechanical properties, such as coefficient of friction, can also be studied by observing surface properties. These quantifiable data can be obtained to ensure the catheter can be used for medical applications.
Compared to optical microscopy and electron microscopy, 3D Non-Contact Profilometry using axial chromatism is highly preferable for characterizing catheter surfaces due to its ability to measure angles/curvature, ability to measure material surfaces despite transparency or reflectivity, minimal sample preparation, and non-invasive nature. Unlike conventional optical microscopy, the height of the surface can be obtained and used for computational analysis; e.g. finding dimensions and removing form to find surface roughness. Having little sample preparation, in contrast to electron microscopy, and non-contact nature also allows for quick data collection without fearing contamination and error from sample preparation.
Objetivo de medición
In this application, the Nanovea 3D Non-Contact Profilometer is used to scan the surface of two catheters: one made of TPE (Thermoplastic Elastomer) and the other made of PVC (Polyvinyl Chloride). The morphology, radial dimension, and height parameters of the two catheters will be obtained and compared.
Resultados y debate
Superficie 3D
Despite the curvature on polymeric tubes, the Nanovea 3D Non-contact profilometer can scan the surface of the catheters. From the scan done, a 3D image can be obtained for quick, direct visual inspection of the surface.
2D Dimensional Analysis
The outer radial dimension was obtained by extracting a profile from the original scan and fitting an arc to the profile. This shows the ability of the 3D Non-contact profilometer in conducting quick dimensional analysis for quality control applications. Multiple profiles can easily be obtained along the catheter’s length as well.
Surface Analysis Roughness
The outer radial dimension was obtained by extracting a profile from the original scan and fitting an arc to the profile. This shows the ability of the 3D Non-contact profilometer in conducting quick dimensional analysis for quality control applications. Multiple profiles can easily be obtained along the catheter’s length as well.
Conclusión
In this application, we have shown how the Nanovea 3D Non-contact profilometer can be used to characterize polymeric tubes. Specifically, surface metrology, radial dimensions, and surface roughness were obtained for medical catheters. The outer radius of the TPE catheter was found to be 2.40mm while the PVC catheter was 1.27mm. The surface of the TPE catheter was found to be rougher than the PVC catheter. The Sa of TPE was 0.9740µm compared to 0.1791µm of PVC. While medical catheters were used for this application, 3D Non-Contact Profilometry can be applied to a large variety of surfaces as well. Obtainable data and calculations are not limited to what is shown.
AHORA, HABLEMOS DE SU SOLICITUD
Evaluación de la dureza de los dientes mediante nanoindentación
Importancia de la nanoindentación para los biomateriales
Con muchos ensayos mecánicos tradicionales (dureza, adherencia, compresión, punción, límite elástico, etc.), los entornos actuales de control de calidad con materiales sensibles avanzados, desde geles hasta materiales quebradizos, requieren ahora un control de mayor precisión y fiabilidad. La instrumentación mecánica tradicional no proporciona el control de carga sensible y la resolución requerida; está diseñada para utilizarse con materiales a granel. A medida que aumentaba el interés por el tamaño del material sometido a ensayo, surgió el desarrollo de Nanoindentación han proporcionado un método fiable para obtener información mecánica esencial en superficies más pequeñas, como la investigación que se realiza con biomateriales. Los retos específicamente asociados a los biomateriales han exigido el desarrollo de ensayos mecánicos capaces de controlar con precisión la carga en materiales extremadamente blandos a quebradizos. Además, se necesitan varios instrumentos para realizar diversas pruebas mecánicas que ahora pueden realizarse en un único sistema. La nanoindentación ofrece una amplia gama de mediciones con una resolución precisa en cargas nanocontroladas para aplicaciones sensibles.
Objetivo de medición
En esta aplicación, el Nanovea Comprobador mecánicoen modo de nanoindentación, se utiliza para estudiar la dureza y el módulo elástico de la dentina, la caries y la pulpa de un diente. El aspecto más crítico de los ensayos de nanoindentación es la fijación de la muestra; en este caso tomamos un diente cortado y lo montamos con epoxi, dejando las tres zonas de interés expuestas para el ensayo.
Resultados y debate
Esta sección incluye una tabla resumen que compara los principales resultados numéricos de las distintas muestras, seguida de los listados de resultados completos, que incluyen cada indentación realizada, acompañados de micrografías de la indentación, cuando están disponibles. Estos resultados completos presentan los valores medidos de dureza y módulo de Young como la profundidad de penetración con sus medias y desviaciones estándar. Debe tenerse en cuenta que pueden producirse grandes variaciones en los resultados en el caso de que la rugosidad de la superficie se encuentre en el mismo intervalo de tamaño que la indentación.
Tabla resumen de los principales resultados numéricos:
Conclusión
En conclusión, hemos mostrado cómo el Nanovea Mechanical Tester, en modo de nanoindentación, proporciona una medición precisa de las propiedades mecánicas de un diente. Los datos pueden utilizarse en el desarrollo de obturaciones que se ajusten mejor a las características mecánicas de un diente real. La capacidad de posicionamiento del Nanovea Mechanical Tester permite obtener un mapa completo de la dureza de los dientes en las distintas zonas.
Utilizando el mismo sistema, es posible probar la tenacidad a la fractura del material de los dientes con cargas más elevadas, de hasta 200N. Se puede utilizar un ensayo de carga de varios ciclos en materiales más porosos para evaluar el nivel de elasticidad restante. El uso de una punta de diamante cilíndrica plana puede proporcionar información sobre el límite elástico en cada zona. Además, con DMA "Análisis Mecánico Dinámico", pueden evaluarse las propiedades viscoelásticas, incluidos los módulos de pérdida y almacenamiento.
El nanomódulo Nanovea es ideal para estas pruebas porque utiliza una respuesta de retroalimentación única para controlar con precisión la carga aplicada. Gracias a ello, el nano módulo también puede utilizarse para realizar ensayos precisos de nano rayado. El estudio de la resistencia al rayado y al desgaste del material dental y de los materiales de obturación se suma a la utilidad general del comprobador mecánico. El uso de una punta afilada de 2 micras para comparar cuantitativamente las marcas en los materiales de obturación permitirá predecir mejor el comportamiento en aplicaciones reales. Las pruebas de desgaste multipaso o de desgaste rotativo directo también son pruebas habituales que proporcionan información importante sobre la viabilidad a largo plazo.
AHORA, HABLEMOS DE SU SOLICITUD
Friction Evaluation at Extreme Low Speeds
Importance of Friction Evaluation at Low Speeds
Friction is the force that resists the relative motion of solid surfaces sliding against each other. When the relative motion of these two contact surfaces takes place, the friction at the interface converts the kinetic energy into heat. Such a process can also lead to wear of the material and thus performance degradation of the parts in use.
With a large stretch ratio, high resilience, as well as great waterproof properties and wear resistance, rubber is extensively applied in a variety of applications and products in which friction plays an important role, such as automobile tires, windshield wiper blades. shoe soles and many others. Depending on the nature and requirement of these applications, either high or low friction against different material is desired. As a consequence, a controlled and reliable measurement of friction of rubber against various surfaces becomes critical.
Objetivo de medición
The coefficient of friction (COF) of rubber against different materials is measured in a controlled and monitored manner using the Nanovea Tribómetro. In this study, we would like to showcase the capacity of Nanovea Tribometer for measuring the COF of different materials at extremely low speeds.
Resultados y debate
The coefficient of friction (COF) of rubber balls (6 mm dia., RubberMill) on three materials (Stainless steel SS 316, Cu 110 and optional Acrylic) was evaluated by Nanovea Tribometer. The tested metal samples were mechanically polished to a mirror-like surface finish before the measurement. The slight deformation of the rubber ball under the applied normal load created an area contact, which also helps to reduce the impact of asperities or inhomogeneity of sample surface finish to the COF measurements. The test parameters are summarized in Table 1.
The COF of a rubber ball against different materials at four different speeds is shown in Figure. 2, and the average COFs calculated automatically by the software are summarized and compared in Figure 3. It is interesting that the metal samples (SS 316 and Cu 110) exhibit significantly increased COFs as the rotational speed increases from a very low value of 0.01 rpm to 5 rpm -the COF value of the rubber/SS 316 couple increases from 0.29 to 0.8, and from 0.65 to 1.1 for the rubber/Cu 110 couple. This finding is in agreement with the results reported from several laboratories. As proposed by Grosch4 the friction of rubber is mainly determined by two mechanisms: (1) the adhesion between rubber and the other material, and (2) the energy losses due to the deformation of the rubber caused by surface asperities. Schallamach5 observed waves of detachment of rubber from the counter material across the interface between soft rubber spheres and a hard surface. The force for rubber to peel from the substrate surface and rate of waves of detachment can explain the different friction at different speeds during the test.
In comparison, the rubber/acrylic material couple exhibits high COF at different rotational speeds. The COF value slightly increases from ~ 1.02 to ~ 1.09 as the rotational speed increases from 0.01 rpm to 5 rpm. Such high COF is possibly attributed to stronger local chemical bonding at the contact face formed during the tests.
Conclusión
In this study, we show that at extremely low speeds, the rubber exhibits a peculiar frictional behavior – its friction against a hard surface increases with the increased speed of the relative movement. Rubber shows different friction when it slides on different materials. Nanovea Tribometer can evaluate the frictional properties of materials in a controlled and monitored manner at different speeds, allowing users to improve fundamental understanding of the friction mechanism of the materials and select the best material couple for targeted tribological engineering applications.
Nanovea Tribometer offers precise and repeatable wear and friction testing using ISO and ASTM compliant rotative and linear modes, with optional high-temperature wear, lubrication and tribo-corrosion modules available in one pre-integrated system. It is capable of controlling the rotational stage at extremely low speeds down to 0.01 rpm and monitor the evolution of friction in situ. Nanovea’s unmatched range is an ideal solution for determining the full range of tribological properties of thin or thick, soft or hard coatings, films, and substrates.
AHORA, HABLEMOS DE SU SOLICITUD
Tribología de polímeros
Introducción
Polymers have been used extensively in a wide variety of applications and have become an indispensable part of everyday life. Natural polymers such as amber, silk, and natural rubber have played an essential role in human history. The fabrication process of synthetic polymers can be optimized to achieve unique physical properties such as toughness, viscoelasticity, self-lubrication, and many others.
Importance of Wear and Friction of Polymers
Polymers are commonly used for tribological applications, such as tires, bearings, and conveyor belts.
Different wear mechanisms occur depending on the mechanical properties of the polymer, the contact conditions, and the properties of the debris or transfer film formed during the wear process. To ensure that the polymers possess sufficient wear resistance under the service conditions, reliable and quantifiable tribological evaluation is necessary. Tribological evaluation allows us to quantitatively compare the wear behaviors of different polymers in a controlled and monitored manner to select the material candidate for the target application.
The Nanovea Tribometer offers repeatable wear and friction testing using ISO and ASTM compliant rotative and linear modes, with optional high-temperature wear and lubrication modules available in one pre-integrated system. This unmatched range allows users to simulate the different work environments of the polymers including concentrated stress, wear, and high temperature, etc.
OBJETIVO DE MEDICIÓN
In this study, we showcased that the Nanovea Tribómetro is an ideal tool for comparing the friction and wear resistance of different polymers in a well-controlled and quantitative manner.
PROCEDIMIENTO DE PRUEBA
The coefficient of friction (COF) and the wear resistance of different common polymers were evaluated by the Nanovea Tribometer. An Al2O3 ball was used as the counter material (pin, static sample). The wear tracks on the polymers (dynamic rotating samples) were measured using a non-contact 3D profilometer and optical microscope after the tests concluded. It should be noted that a non-contact endoscopic sensor can be used to measure the depth the pin penetrates the dynamic sample during a wear test as an option. The test parameters are summarized in Table 1. The wear rate, K, was evaluated using the formula K=Vl(Fxs), where V is the worn volume, F is the normal load, and s is the sliding distance.
Please note that Al2O3 balls were used as the counter material in this study. Any solid material can be substituted to more closely simulate the performance of two specimens under actual application conditions.
RESULTADOS Y DEBATE
Wear rate is a vital factor for determining the service lifetime of the materials, while the friction plays a critical role during the tribological applications. Figure 2 compares the evolution of the COF for different polymers against the Al2O3 ball during the wear tests. COF works as an indicator of when failures occur and the wear process enters a new stage. Among the tested polymers, HDPE maintains the lowest constant COF of ~0.15 throughout the wear test. The smooth COF implies that a stable tribo-contact is formed.
Figure 3 and Figure 4 compare the wear tracks of the polymer samples after the test is measured by the optical microscope. The In-situ non-contact 3D profilometer precisely determines the wear volume of the polymer samples, making it possible to accurately calculate wear rates of 0.0029, 0.0020, and 0.0032m3/N m, respectively. In comparison, the CPVC sample shows the highest wear rate of 0.1121m3/N m. Deep parallel wear scars are present in the wear track of CPVC.
CONCLUSIÓN
The wear resistance of the polymers plays a vital role in their service performance. In this study, we showcased that the Nanovea Tribometer evaluates the coefficient of friction and wear rate of different polymers in a
well-controlled and quantitative manner. HDPE shows the lowest COF of ~0.15 among the tested polymers. HDPE, Nylon 66, and Polypropylene samples possess low wear rates of 0.0029, 0.0020 and 0.0032 m3/N m, respectively. The combination of low friction and great wear resistance makes HDPE a good candidate for polymer tribological applications.
The In-situ non-contact 3D profilometer enables precise wear volume measurement and offers a tool to analyze the detailed morphology of the wear tracks, providing more insight into the fundamental understanding of wear mechanisms
AHORA, HABLEMOS DE SU SOLICITUD
Honeycomb Panel Surface Finish with 3D Profilometry
INTRODUCCIÓN
Roughness, porosity, and texture of the honeycomb panel surface are critical to quantify for the final panel design. These surface qualities can directly correlate to the aesthetics and functional characteristics of the panel surface. A better understanding of the surface texture and porosity can help optimize the panel surface processing and manufacturability. A quantitative, precise, and reliable surface measurement of the honeycomb panel is needed to control surface parameters for application and painting requirements. The Nanovea 3D Non-Contact sensors utilize unique chromatic confocal technology capable of precisely measuring these panel surfaces.
OBJETIVO DE MEDICIÓN
In this study, the Nanovea HS2000 platform equipped with a high-speed Line Sensor was used to measure and compare two honeycomb panels with different surface finishes. We showcase the Nanovea perfilómetro sin contacto’s ability to provide fast and precise 3D profiling measurements and comprehensive in-depth analysis of the surface finish.
RESULTADOS Y DEBATE
The surface of two honeycomb panel samples with varied surface finishes, namely Sample 1 and Sample 2, were measured. The false color and 3D view of the Samples 1 and 2 surfaces are shown in Figure 3 and Figure 4, respectively. The roughness and flatness values were calculated by advanced analysis software and are compared in Table 1. Sample 2 exhibits a more porous surface compared to Sample 1. As a result, Sample 2 possesses a higher roughness Sa of 14.7 µm, compared to an Sa value of 4.27 µm for Sample 1.
The 2D profiles of the honeycomb panel surfaces were compared in Figure 5, allowing users to have a visual comparison of the height change at different locations of the sample surface. We can observe that Sample 1 has a height variation of ~25 µm between the highest peak and lowest valley location. On the other hand, Sample 2 shows several deep pores across the 2D profile. The advanced analysis software has the ability to automatically locate and measure the depth of six relatively deep pores as shown in the table of Figure 4.b Sample 2. The deepest pore amongst the six possesses a maximum depth of nearly 90 µm (Step 4).
To further investigate the pore size and distribution of Sample 2, porosity evaluation was performed and discussed in the following section. The sliced view is displayed in Figure 5 and the results are summarized in Table 2. We can observe that the pores, marked in blue color in Figure 5, have a relatively homogeneous distribution on the sample surface. The projected area of the pores constitutes 18.9% of the whole sample surface. The volume per mm² of the total pores is ~0.06 mm³. The pores have an average depth of 42.2 µm, and the maximum depth is 108.1 µm.
CONCLUSIÓN
In this application, we have showcased that the Nanovea HS2000 platform equipped with a high-speed Line Sensor is an ideal tool for analyzing and comparing the surface finish of honeycomb panel samples in a fast and accurate manner. The high-resolution profilometry scans paired with an advanced analysis software allow for a comprehensive and quantitative evaluation of the surface finish of honeycomb panel samples.
The data shown here represents only a small portion of the calculations available in the analysis software. Nanovea Profilometers measure virtually any surface for a wide range of applications in the Semiconductor, Microelectronic, Solar, Fiber Optics, Automotive, Aerospace, Metallurgy, Machining, Coatings, Pharmaceutical, Biomedical, Environmental and many other industries.
AHORA, HABLEMOS DE SU SOLICITUD
Medición de la relajación de tensiones mediante nanoindentación
INTRODUCCIÓN
Viscoelastic materials are characterized as having both viscous and elastic material properties. These materials are subject to time-dependent stress decrease (stress ‘relaxation’) under constant strain, leading to a significant loss of initial contact force. Stress relaxation is dependent on the type of material, texture, temperature, initial stress, and time. Understanding stress relaxation is critical in selecting optimal materials that have the strength and flexibility (relaxation) required for specific applications.
Importance of Stress Relaxation Measurement
As per ASTM E328i, “Standard Test Methods for Stress Relaxation for Materials and Structures”, an external force is initially applied on a material or structure with an indenter until it reaches a predetermined maximum force. Once the maximum force is reached, the position of the indenter is held constant at this depth. Then the change in external force necessary to maintain the indenter’s position is measured as a function of time. The difficulty in stress relaxation testing is maintaining the depth constant. The Nanovea Mechanical Tester’s nanoindentación module accurately measures the stress relaxation by applying a closed (feedback) loop control of the depth with a piezo-electric actuator. The actuator reacts in real-time to keep the depth constant, while the change in load is measured and recorded by a highly sensitive load sensor. This test can be performed on virtually all types of materials without the need for stringent sample dimension requirements. Additionally, multiple tests can be performed on a single flat sample to ensure test repeatability
OBJETIVO DE MEDICIÓN
In this application, the Nanovea Mechanical Tester’s nanoindentation module measures the stress relaxation behavior of an acrylic and copper sample. We showcase that the Nanovea Comprobador mecánico is an ideal tool for evaluating the time-dependent viscoelastic behavior of polymer and metal materials.
CONDICIONES DE ENSAYO
The stress relaxation of an acrylic and a copper sample was measured by the Nanovea Mechanical Tester’s nanoindentation module. Different indentation loading rates were applied ranging from 1 to 10 µm/min. The relaxation was measured at a fixed depth once the target maximum load was reached. A 100 second holding period was implemented at a fixed depth and the change in load was recorded as the holding time elapsed. All of the tests were conducted at ambient conditions (room temperature of 23 °C) and the indentation test parameters are summarized in Table 1.
RESULTADOS Y DEBATE
Figure 2 shows the evolution of displacement and load as a function of time during the stress relaxation measurement of an acrylic sample and an indentation loading rate of 3 µm/min as an example. The entirety of this test can be broken down into three stages: Loading, Relaxation and Unloading. During the Loading stage, the depth linearly increased as the load progressively increased. The Relaxation stage was initiated once the maximum load was reached. During this stage a constant depth was maintained for 100 seconds by using the closed feedback loop depth control feature of the instrument and it was observed that the load decreased over time. The entire test concluded with an unloading stage in order to remove the indenter from the acrylic sample.
Additional indentation tests were conducted using the same indenter loading rates but excluding a relaxation (creep) period. Load vs. displacement plots were acquired from these tests and were combined in the graphs in Figure 3 for the acrylic and copper samples. As the indenter loading rate decreased from 10 to 1 µm/min, the load-displacement curve shifted progressively towards higher penetration depths for both Acrylic and Copper. Such a time-dependent increase in strain results from the viscoelastic creep effect of the materials. A lower loading rate allows a viscoelastic material to have more time to react to the external stress it experiences and to deform accordingly..
The evolution of load at a constant strain using different indentation loading rates were plotted in Figure 4 for both materials tested. The load decreased at a higher rate in the early stages of the relaxation stage (100 second hold period) of the tests and slowed down once the hold time reached ~50 seconds. Viscoelastic materials, such as polymers and metals, exhibit greater load loss rate when they are subjected to higher indentation loading rates. The load loss rate during relaxation increased from 51.5 to 103.2 mN for Acrylic, and from 15.0 to 27.4 mN for Copper, respectively, as the indentation loading rate increased from 1 to 10 µm/min, as summarized in Figure 5.
As mentioned In ASTM Standard E328ii, the major problem encountered in stress relaxation tests is an instrument’s inability of maintaining a constant strain/depth. The Nanovea Mechanical Tester provides excellent accurate stress relaxation measurements due to its ability to apply a closed feedback loop control of the depth between the fast acting piezo-electric actuator and the independent capacitor depth sensor. During the relaxation stage, the piezo-electric actuator adjusts the indenter to maintain its constant depth constraint in real-time while the change in load is measured and recorded by an independent high precision load sensor.
CONCLUSIÓN
The stress relaxation of an acrylic and a copper sample were measured using the nanoindentation module of the Nanovea Mechanical Tester at different loading rates. A greater maximum depth is reached when indentations are performed at lower loading rates due to the creep effect of the material during loading. Both the acrylic and the copper sample exhibit stress relaxation behavior when the indenter position at a targeted maximum load is held constant. Larger changes in load loss during the relaxation stage were observed for the tests with higher indentation loading rates.
The stress relaxation test produced by the Nanovea Mechanical Tester showcase the instruments ability to quantify and reliably measure the time-dependent viscoelastic behavior of polymer and metal materials. It has an unmatched multi-function Nano and Micro modules on a single platform. Humidity and temperature control modules can be paired with these instruments for environmental testing capabilities applicable to a wide range of industries. Both the Nano and Micro modules include scratch testing, hardness testing, and wear testing modes, providing the widest and most user-friendly range of mechanical testing capabilities available on a single system.
AHORA, HABLEMOS DE SU SOLICITUD
Comprensión de los fallos del revestimiento mediante ensayos de rayado
Introducción:
La ingeniería de superficies de los materiales desempeña un papel importante en diversas aplicaciones funcionales, que van desde el aspecto decorativo hasta la protección de los sustratos contra el desgaste, la corrosión y otras formas de ataque. Un factor importante y primordial que determina la calidad y la vida útil de los revestimientos es su fuerza cohesiva y adhesiva.
High Speed Scanning w/ Non-contact Profilometry
Introducción:
Quick and easy set-up surface measurements save time, effort and are essential for quality control, research and development and production facilities. The Nanovea Non-Contact Profilometer is capable of performing both 3D & 2D surface scans to measure nano to macro scale features on any surface, providing broad range usability.
