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The joining of thermoplastics through welding offers numerous advantages over mechanical joining. Most importantly, it eliminates the use of costly fasteners and has only a limited effect on the strength of the parts being joined. Since it does not require the introduction of holes, loading pins, and the associated stress concentrations, a specific form of welding, friction stir welding (FSW), was investigated for the creation of butt joints of unreinforced polyphenylene sulfide (PPS) and short carbon fiber (CF)-reinforced polyetheretherketone (PEEK) plates. Unlike metals, analytical models and experimental results show that the heat generated by the FSW tool is insufficient to produce the heat required to weld thermoplastic materials. Therefore, a second heat source is required for preheating these thermoplastics. In this research, a resistance type surface heater was placed at the bottom of two identical weld pieces to produce good quality welds. Two types of shoulder design such as rotating shoulder and stationary shoulder were developed in this study. Taguchi's design of experiment method was utilized to develop the welding process, where heating duration, material temperature, tool rotational speed, and tool traverse speed were used as the welding parameters. One of the process parameters, tool traverse speed, had significant influence on the tensile strength of PPS samples. While PPS sample showed relatively lower tensile strength with higher traverse speed, short CF-reinforced PEEK samples had higher tensile strength with a higher traverse speed. In addition to tensile tests, fracture toughness tests were performed for both PPS and PEEK samples to observe the influence of unwelded segments in the welded parts. In this study, joint efficiency of PEEK samples was found to be higher than that of PPS samples. Micrographs of PEEK samples showed uniform homogenous mixture of part materials. [ABSTRACT FROM AUTHOR]

The local deformation response of low carbon steel subjected to uniaxial tensile loading is investigated, and the local strain field at sub-grain scale is obtained using high-spatial-resolution digital image correlation. The implemented digital image correlation method enables the observation and study of inhomogeneous deformation response at microstructural levels. Detailed local deformation mechanisms including mesoscopic slip bands are captured. Furthermore, the local information is used for the determination of representative volume element size in polycrystalline low carbon steel. To obtain the representative volume element size, we proposed and successfully implemented a strain variation method. Further, the influence of global strain on the local deformation mechanisms and representative volume element size is discussed. The challenges associated with the local strain measurement using digital image correlation are also discussed. [ABSTRACT FROM AUTHOR]

The nonlinear mechanical response of 45° woven composites is studied using full-field strain measurements. First, carbon fabric samples without an epoxy matrix are prepared and tested to evaluate the deformation response of the fiber tows in the absence of internal resistance imposed by the epoxy matrix. Next, the effect of the epoxy matrix is examined by fabricating and testing 45° single-ply carbon fiber reinforced composite laminas. Homogeneous strain fields with minimal resistance against external loads are observed in fabric samples without epoxy. The in-plane rotation of fiber tows in the carbon fabric samples varies linearly with the applied global strain. On the other hand, the development of scissoring action in single-ply composite laminas is shown to cause severe shearing of the epoxy entrapped between the orthogonal fiber tows, leading to the outward protrusion of epoxy from the surface of the lamina. The scissoring effect is correlated with different stages of deformation in a highly nonlinear stress–strain response. Finally, similar tests performed on three-ply laminates reveal that the abovementioned matrix protrusion leads to accelerated delamination in 45° laminates at global strains lower than those in single-ply laminas. The underlying mechanisms for scissoring-induced matrix protrusion are discussed using a simple analytical model. [ABSTRACT FROM AUTHOR]

A multiscale experimental approach is introduced that facilitates correlating globally applied stress to the local material response at yarn scale. Using a high-resolution optical digital image correlation, low and high strain zones in off-axis woven composite samples loaded in uniaxial tension are identified and the corresponding full-field strains are quantified. The local strain response quantified over low and high strain domains are used along with the continuum scale deformation to establish a correlation between global and local deformation behavior as a function of fiber orientation. In addition, global stress-local strain curves are extracted for low and high strain domains at different fiber orientation angles. A simple plasticity model in conjunction with the obtained stress-strain curves is implemented and utilized to develop a phenomenological model that enables correlating global stress with the locally developed strain at different locations in a composite specimen subjected to off-axis tensile load. [ABSTRACT FROM AUTHOR]

The gradual damage initiation and evolution in quasi-isotropic (±45, 90, 0) s carbon fiber laminate composites under a quasi-static tension loading is investigated experimentally. The full-field strains across the thickness of the laminate as a function of applied tensile load was acquired using high spatial resolution digital image correlation. The chnage in strain during the initiation and growth of micro-cracks is evaluated, and the influence of strain redistribution over the surrounding layers is analyzed. The local failure mechanism is investigated and the influence of the local damage on the global mechanical response of the composite is explored. It was found that the failure is initiated as a matrix crack in the most off-axis plies, gradually propagate to the nearby ply and eventually grow to a complete delamination. Further, it was found that the shear lagging induced between two adjacent plies has a significant effect in directing the matrix crack growth and inducing delamination. [ABSTRACT FROM AUTHOR]

Ultra-high-speed and high spatial resolution digital image correlation based experiments are performed to understand the sub grain level local failure mechanisms in polymer bonded explosives under dynamic loading. Polymer bonded sugar that mimics the mechanical properties of polymer bonded explosives is used in this study. The experiments are conducted in a split Hopkinson pressure bar setup at an intermediate strain rate. From the digital image correlation analyses, high strain localization was observed predominantly in the regions filled by the polymer binder surrounding the sugar crystals. The damage evolution was quantified by calculating the Poisson's ratio and volumetric strain as a function of loading. It was observed that the damage incubation is started at a very small global strain and causes mechanical softening in the material that leads to shear band formation. Also, the possible hotspot mechanism in the material was seen to be frictional heating of crystals and de-bonding of the polymer binder. [ABSTRACT FROM AUTHOR]

An experimental approach based on Digital Image Correlation (DIC) is successfully applied to predict the uniaxial stress-strain response of 304 stainless steel specimens subjected to nominally uniform temperatures ranging from room temperature to 900 °C. A portable induction heating device equipped with custom made water-cooled copper coils is used to heat the specimen. The induction heater is used in conjunction with a conventional tensile frame to enable high temperature tension experiments. A stereovision camera system equipped with appropriate band pass filters is employed to facilitate the study of full-field deformation response of the material at elevated temperatures. Using the temperature and load histories along with the full-field strain data, a Virtual Fields Method (VFM) based approach is implemented to identify constitutive parameters governing the plastic deformation of the material at high temperature conditions. Results from these experiments confirm that the proposed method can be used to measure the full field deformation of materials subjected to thermo-mechanical loading. [ABSTRACT FROM AUTHOR]

A systematic approach is proposed to estimate the length scales of the representative volume element (RVE) in orthogonal plain woven composites. The approach is based on experimental full-field deformation measurements at mesoscopic scales. Stereovision digital image correlation (DIC) is conducted to determine the full-field strain distribution in on- and off-axis specimens loaded axially in tension. A sensitivity analysis is carried out to optimize the image correlation parameters. Using the optimized set of image correlation parameters, full-field strains are measured and used in conjunction with a simple strain averaging algorithm to identify the length scales at which globally applied and spatially-averaged local strains converge in values. The size of a virtual window containing local strain data, the average of which has the same value as the global strain, is identified as the RVE dimensions for the examined material. The smallest RVE sizes found in this work are shown to be both strain and angle dependent. The largest RVE dimension obtained is reported as a unique, strain and orientation insensitive RVE size for the woven composite examined. [ABSTRACT FROM AUTHOR]

As part of an effort to predict wrinkling of carbon-fiber tows during automated fiber placement, the cohesive zone traction–separation relations for two carbon fiber epoxy prepreg tows are quantified for Mode I and Mode II loading using a rigid double cantilever beam (RDCB) specimen. An explicit expression for normal traction versus normal separation ( σ vs δ n ) and tangential traction versus tangential separation (τ vs δ t) are derived using static equilibrium equations for an RDCB considering a compressive zone ahead of the process zone. The traction–separation relationships are in term of quantities that can be measured using a full field measurement technique (StereoDIC). The baseline traction–separation relationships in this work are obtained using conditions representative of those experienced by an uncured tow undergoing automated fiber placement (AFP) onto a substrate of a similar material with layup temperature T = 40 ∘ C , pressure p = 1 MPa and contact time t = 1 s. The RDCB specimen is loaded in displacement control at a constant load line displacement rate of 0.3 mm/min. Speckle images for StereoDIC are captured using stereo vision systems equipped for capturing images of the RDCB specimen with a field of view of 100 mm × 75 mm . Analysis of the data obtained for Mode I and Mode II loading shows that the Mode I energy release rate G I = 120 J / m 2 and Mode II energy release rate G II = 255 J / m 2 , with the maximum normal traction σ max = 0.50 MPa and the maximum shear traction τ max = 0.35 MPa . [ABSTRACT FROM AUTHOR]

Property gradation along a crack front makes conventional fracture mechanics analyses challenging. This issue is addressed in the present study through a combination of full-field measurements and modeling. We develop a novel experimental setup that consists of a synchronous dual Digital Image Correlation (DIC) system, facilitating in situ measurement of displacement and strain fields on both sides of a transversely precracked multi-layered structure subjected to uniaxial tensile load. By measuring the evolution of stress intensity factors developed on the opposite sides of the sample, we explore the mechanisms of crack initiation and propagation in the examined graded sample. Our experimental measurements are supplemented by a finite element analysis that elucidates the deformation and fracture response of the internal layers for which surface measurement is not possible. Finally, based on experimental and numerical observations, we develop a simple model that allows for prediction of critical far-field loads at which transversely graded structures fail. The capability of our proposed model in predicting tensile failure loads is demonstrated through a brief study of the influence of gradient function on the load bearing and fracture resistance in various graded structures. [ABSTRACT FROM AUTHOR]

Highlights • Global material response was found to be dependent on initial grain orientation. • Contribution of intergranular to intragranular deformation was large in cast Mg. • Strain rate sensitivity was related to the amount of grain boundary deformation. Abstract Due to the presence of weak grain boundaries as well as significantly coarse grain structure with minimal deformability, grain boundary cracking is almost an inevitable source of failure when a cast magnesium-based alloy is deformed at low homologous temperatures. The main objective in this work is to quantitatively investigate the contribution of inter- and intragranular deformation to the macroscale deformability and ductility of nominally pure as-cast magnesium subjected to quasi-static and dynamic loading. The proposed mesoscale full-field measurement approach is first presented and verified through measurements carried out to investigate deformation and grain boundary cracking in cast magnesium subjected to quasi-static loading. The method is then extended into the analysis of mesoscale deformation and failure under dynamic loading conditions using an experimental setup consisting of a split Hopkinson pressure bar (SHPB) and a high-speed imaging system. In both cases, the effect of the initial grain configuration on the local deformation response of Mg is investigated. The results indicate that the contribution of grain boundary region deformation to the total deformation exerted on the Mg samples is significant and depends on the initial grain configuration. Also, the strain rate sensitivity of the material is found to be dominated by the material deformation in the vicinity of grain boundaries. [ABSTRACT FROM AUTHOR]

A great-deal of literature is available in the study of compaction wave propagation in cellular materials. However, experimental investigations concerning the spatial variation of the deformation features of compaction waves are limited. In this study, the formation and propagation of compaction wave in a low density polymeric foam under intermediate velocity projectile impact loading is investigated experimentally. The results are discussed in terms of the compaction wave characteristic parameters such as compaction wave velocity, axial strain, particle velocity, etc. In addition, spatial distribution of inertia stress during compaction wave propagation, and the critical velocity required to form shock are estimated. The stress jump across the compaction wave is also calculated using an inertia stress analysis and compared with the shock theory. It was observed that an elastic precursor propagates, at a velocity of 740 m/s, along the material upon impact, and it decays as it propagates along the specimen. Whereas, the compaction wave formed following the elastic precursor was propagated at a constant velocity much slower than the elastic precursor. Inertia stress calculations shows that the fast moving elastic precursor is reflected from the distal end and reduces the inertia component of the total stress. On the other hand, the compaction thickness is seen to be approximately constant during the entire duration of the compaction wave propagation after the achievement of the quasi-steady condition. [ABSTRACT FROM AUTHOR]

The traction-separation law under Mode I loading for a polymer modified bitumen commonly used as an adhesive for 3–tab roofing shingles is quantified. Double cantilever experiments are performed at three different loading rates (0.03 mm/min, 0.3 mm/min and 3 mm/min). Load-displacement measurements are synchronized with speckle image acquisition and the data analyzed to determine (a) J-integral, (b) cohesive zone end opening displacement and (c) the crack opening displacement (COD) as a function of crack extension. Imaging is performed using two stereo vision systems equipped for capturing speckle images of the DCB specimen at two different magnifications with fields of view of (a) 14 mm × 12 mm and (b) 170 mm × 140 mm. The stereo vision system used to acquire data at higher magnification is mounted on a translation stage and focused on a region close to the crack tip as the crack propagated. This stereo vision system is used to measure the strain fields near the crack tip and for measurement of crack opening displacement (COD) at 1 mm behind the current crack tip for a range of crack extensions. The second stereo vision system is used to visualize the process zone size and measure the strain fields over larger fields of view ahead of the crack tip. Assessment of the fracture surface for lower loading rates (0.03 mm/min and 0.3 mm/min) revealed a ductile type fracture (rough surface due to void growth in the process zone). For the highest loading rate (3 mm/min), the fracture surface is typical of the type seen during brittle fracture (shiny surface with striations), with intermittent rapid crack propagation events followed by crack arrest along clearly visible arrest fronts. Analysis of the data obtained for the two slower loading rates that exhibited ductile fracture throughout the entire growth process shows that the energy release rate G c d  = 70 J/m 2 , and the final separation, δ c d  = 250 µm for the slowest loading rate of 0.03 mm/min and, G c d  = 120 J/m 2 , and the final separation, δ c d  = 250 µm for 0.3 mm/min loading rate. For the highest loading rate, which exhibited nominally brittle fracture, the energy release rate G c b  = 10 J/m 2 , and the final separation δ c d  = 1.5 µm. The peak cohesive stresses during ductile and brittle fracture are determined to be σ d  = 0.7 MPa and σ b  = 9.6 MPa, respectively, for loading rates of 0.3 mm/min and 3 mm/min, respectively. Finally, COD at the onset of crack growth measured at 1.00 mm behind the moving crack tip for the loading rate of 0.3 mm/min, COD d  ≈ 0.30 mm, remaining constant for crack lengths, a, in the range 25 mm ≤ a ≤ 165 mm. [ABSTRACT FROM AUTHOR]

Using a unidirectional heat transfer apparatus, the roles of nanoparticle geometry, loading, dispersion and temperature on the thermal conductivity of polymer nanocomposites are investigated. The polymer nanocomposites (PNC) consist of epoxy matrices filled with silica nanopowder and carbon nanotubes, respectively, as well as poly (2-vinylpyridine) (P2VP) matrices loaded with silica nanoparticles. First, it is shown that thermal conductivity generally increases with nanofiller loading. These results are also reasonably described by the three phase Lewis-Nielsen or Halpin-Tsai analytical models. More importantly, it has been also demonstrated that the thermal conductivity of the polymer nanocomposites greatly depends on the dispersion state of the nanofillers. Furthermore, the effect of temperature on the thermal behavior of PNCs is briefly discussed. These results emphasize the important role of nanoparticles content and dispersion state on the thermal characteristics of polymer nanocomposites, which can be used to design composite materials with tunable thermal behavior. [ABSTRACT FROM AUTHOR]

For the first time, the vision-based measurement method Stereo Digital Image Correlation (StereoDIC) is applied successfully to quantitatively assess the response of asphalt shingles installed in a model roofing system and subjected to hurricane velocity winds. By mounting a low profile asphalt-shingled plywood roof facsimile without building firmly to a rigid steel frame and supplying sustained winds of 67.1 m/s perpendicular to the leading edge region, StereoDIC measurements were obtained at 1 Hz to measure the full-field uplift displacements for shingles sealed using either single or double sealant strips. By varying the sealant activation process (time and temperature), the effect of installation in winter and summer seasons is also quantified throughout the wind loading process. Results indicate that with lower temperature sealant activation, both single and double sealant shingles sustained catastrophic failure within a short time when the wind speed reached 67.1 m/s, with the double sealant system lasting for about 500 s; visual inspection of the separation surfaces for the low temperature activation showed large specular reflecting regions, indicating either no bonding or minimal adherence. For a higher sealant activation temperature, (a) both single and double sealant shingles remained intact for more than 2 h in 67.1 m/s wind speeds, with no sealant separation observed and (b) displacements for the shingle with double sealant strips were significantly lower than for the single sealant system, confirming the efficacy of a double sealant strip system. As a general observation, StereoDIC measurements clearly show that shingle uplift displacement is not constant across the width of a shingle tab, with the edges of the shingle (tab cutout regions) having significantly larger uplift displacements that may serve as sealant separation initiation sites. • Stereo digital image correlation employed for in situ measurement of uplift displacement of asphalt shingles. • Asphalt shingles sealed using single and double sealant strips and at two different activation temperatures are evaluated. • Lower activation temperature can result in partial bonding of sealant; one of the major causes of premature failure. • Corners of the shingle undergo significantly larger uplift displacements. [ABSTRACT FROM AUTHOR]

This study investigates the high loading rate behavior of adhesively bonded carbon/epoxy composite joints under mode I loading. A computationally guided experimental setup is developed to study the mode-I behavior of composite joints in the range of quasi-static to high loading rates. A double cantilevered beam specimen with wedge insert type loading setup is used to conduct quasi-static and dynamic experiments. For the dynamic loading, a modified split Hopkinson bar is used to load the sample at high rates. The local deformation field is measured using high Spatio-temporal resolution digital image correlation (DIC). From the experiments, the mode-I energy release rate is calculated from the load, crack extension and crack root rotation data measured using load cell and DIC. A decrease in the initiation fracture toughness with increase in loading rate was observed which is attributed to the strain rate dependent behavior of the epoxy-based film adhesive. For both quasi-static and high loading rates, a mixed adhesive-cohesive failure is observed from the fracture surface analysis. Image 1 [ABSTRACT FROM AUTHOR]

Background: Neonatal pain has been underrecognized and undertreated in many settings with the youngest children and neonates suffering the greatest consequences. Despite recent advancements in the assessment and therapy of children's pain, a knowledge-to-practice gap still exists especially in developing nations including our country Ethiopia., Objectives: To assess knowledge, practice, and associated factors towards neonatal pain management among health care professionals working at neonatal intensive care units of public hospitals in North Shoa Zone, Amhara regional state, Ethiopia., Method: Facility-based cross-sectional study design was conducted among health care professionals working at NICU in all public hospitals in North Shoa Zone, from May 9, 2023, to May 23, 2023. Data were collected using a self-administered questionnaire from 123 health care professionals working at NICUs in eleven public hospitals. The collected data were checked and entered into EPI data version 3.1 and then exported to SPSS version 25 for further descriptive and logistic regression analysis. Data are summarized using descriptive statistics and presented using narrations, tables, and graphs., Result: The study reveals that 48% of health care professionals possessed adequate knowledge, while only 5.7% demonstrated good practices in neonatal pain management. Factors significantly associated with better neonatal pain management practices included having good knowledge of neonatal pain management (AOR = 3.36, 95% CI [1.19-9.49]), a higher educational level (AOR = 4.48, 95% CI [1.62-13.88]), and the availability of a pain scale assessment tool in the neonatal unit (AOR = 3.91, 95% CI [1.50-10.20]). Moreover, the type of profession, specifically being a nurse (AOR = 0.23, 95% CI [0.08-0.66]), was significantly associated with knowledge of neonatal pain management., Conclusion: Health care professionals' knowledge and practice regarding neonatal pain management are insufficient. Multisectoral collaboration is essential to enhance their knowledge and skills and improve the availability of pain scale assessment tools and supportive materials., Competing Interests: The authors declare that they have no conflicts of interest., (Copyright © 2024 Abraraw Admasu Jember et al.)