This study conducts experimental and numerical studies on the progressive damage occurring during the drilling of composite laminates. In particular, this work focuses on push-out delamination, which ...occurs at the interface around the drill-exit and is the most critical damage suffered during the drilling process. To investigate the damage progression mechanisms, penetration and interruption drilling tests are performed on composite laminate consisting of quasi-isotropic CFRP plies and fabric GFRP ply (bottom side). After drilling tests, the damage evolution is evaluated using X-ray computed tomography and optical microscopy. Based on the experimental results, a simplified simulation model is established, and damage progression simulation is performed using an explicit dynamic finite element method. The results show that the bending deformation in the bottom two plies triggers the propagation of push-out delamination. Therefore, the extent of delamination is significantly affected by the thickness and the material properties of the bottom plies.
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This study seeks to establish a high-fidelity mesoscale simulation methodology that can predict the progressive damage and resultant failure of carbon fiber reinforced plastic laminates (CFRPs). In ...the proposed scheme, the plastic behavior (i.e., pre-peak nonlinear hardening in the local stress-strain response) is characterized through the pressure-dependent elasto-plastic constitutive law. The evolution of matrix cracking and delamination, which result in post-peak softening in the local stress-strain response, is modeled through cohesive zone models (CZM). The CZM for delamination is introduced through an interface element, but the CZM for matrix cracking is introduced through an extended finite element method (XFEM). Additionally, longitudinal failure, which is dominated by fiber breakage and typically depends on the specimen size, is modeled by the Weibull criterion. The validity of the proposed methodology was tested against an off-axis compression (OAC) test of unidirectional (UD) laminates and an open-hole tensile (OHT) test of quasi-isotropic (QI) laminates. Finally, sensitivity studies were performed to investigate the effect of plasticity and thermal residual stress against the prediction accuracy in the OHT simulation.
Although current preoperative fasting guidelines apply restrictions to drinks containing milk because of delayed gastric emptying, the safe volume of milk that can be consumed up to 2 h before ...surgery on a theoretical basis has not yet been defined. We aimed to determine whether delayed gastric emptying depended mainly on the total amount of calories irrespective of compositional differences between milk and clear fluids.
We prepared five beverages with a uniform volume (500 ml) and step-wise increments in calories (0, 220, and 330 kcal), comprised mainly of non-human milk, pulpless orange juice, water, and gum syrup. The gastric emptying rate of each beverage was determined by ultrasound measurements of the gastric antral cross-sectional area after their ingestion by eight healthy fasting volunteers.
The emptying rates of 500 ml of orange juice and 330 ml of non-human milk with 170 ml of water (both were 220 kcal) from the stomach were similar. Furthermore, 450 ml of orange juice with 50 ml of gum syrup and 500 ml of non-human milk (both were 330 kcal) left the stomach at similar rates. The 220 kcal beverages emptied faster than the 330 kcal beverages.
There were no significant differences in liquid gastric emptying after drinking equal volumes of either orange juice or milk as long as both had the same amount of calories. Liquid gastric emptying depends chiefly on the total caloric content.
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A micro-scale simulation scheme is developed in this study to evaluate in-situ damage and strength properties of CFRP laminates with various ply thicknesses. To capture both the initiation and ...propagation of transverse cracks, the microscopic random fiber configuration and the constraint effect from neighboring plies should be carefully considered. This study considers the representative volume element (RVE), consisting of the 'inhomogeneous' ply in which the solid elements individually modeled the fiber and matrix, and the 'homogenized' plies, homogeneously modeled by the shell elements. Matrix damage and debonding between fiber and matrix were modeled in the inhomogeneous ply to reproduce transverse crack propagation. Furthermore, in the RVE simulation, the key degree of freedom method was incorporated to evaluate the in-situ properties of each ply effectively. The validity of the proposed tool was examined by comparing the predicted cracking behavior with the results of unidirectional tensile tests on cross-ply laminates having different 90º ply thicknesses. The effects of ply thickness on the in-situ damage and strength properties of cross-ply laminates were numerically investigated, and the continuum damage mechanics model for thin-ply laminate was proposed based on the numerical results.
Progressive damages in the open-hole compression (OHC) tests of composite laminates were experimentally and numerically studied. In the experiment, the failure mechanisms were investigated via in ...situ microscopy observation, digital image correlation, X-ray radiography, and X-ray computed tomography. Three layups were tested to examine the dependence of progressive damages on the layups. Additionally, numerical simulation was conducted to comprehensively examine the failure mechanisms. In the numerical studies, the simulation scheme, considering the plasticity, kink-band failure, multiple intra-laminar cracks, and delamination, was developed. From the experiment and simulation, it is clarified that the kink-band is initiated and propagated by the combined stress states consisting of longitudinal compression and in-plane shear around the intra-laminar cracks. Therefore, for the high-fidelity OHC simulation in various layups, it is necessary to capture the interaction between kink-band and intra-laminar cracks by considering the combined stress state in the kink-band failure criteria and modeling the multiple intra-laminar cracks.
•This study focused on the high-velocity impact on composite laminates.•Phenomenological mesomodeling based on the experiment was presented.•In the experiment, diffuse matrix cracks and dominant ...matrix cracks were observed.•The presented mode used continuous and discrete damage models for two crack types.•The presented mode was more accurate and efficient than the conventional models.
This study presents both experimental testing and phenomenological mesomodeling for composite laminates under high-velocity impact. First, we conducted high-velocity impact tests on CFRP laminates and investigated the penetration and damage behaviors. Three kinds of internal damage were observed: fiber breakage, matrix cracking, and delamination. The observed matrix cracks were classified into two categories: multiple (diffuse) cracks around the impact point and large (dominant) cracks on the bottom ply. A phenomenological mesomodel was then developed based on these experiment observations. In the presented model, both continuous and discrete damage models were implemented for modeling two crack configurations. For comparison, we presented two conventional models (one using only the discrete damage model, and the other using only the continuous damage model). To validate the presented model, high-velocity impact simulations were performed, and the predicted results were compared with experiment and conventional models in terms of the damage area and distribution.
Summary
We previously demonstrated that the gastric emptying time of different liquids with the same volume mainly depended on their energy content, regardless of differences in composition. In this ...crossover study, we investigated whether the same applies when soluble solid foods are ingested with water. Ten healthy volunteers ingested one of five test diets consisting of two test meals (Calorie Mate® 100 and 200 kcal) and three test solutions (water and glucose solutions of 100 and 200 kcal), each given in a volume of 400 ml, and then underwent ultrasonography to measure the gastric antral cross‐sectional area every 10 min for 120 min. The gastric emptying time was defined as the time for the antral cross‐sectional area to revert to its initial value. When test diets with the same energy content were ingested, the gastric emptying curves were nearly identical, regardless of whether the original form was solid or liquid. The median (IQRrange) gastric emptying times of Calorie Mate® of 100 kcal with water vs. isocaloric glucose solution were 65 (60–78 50–80) vs. 65 (60–70 50–80) min (p = 0.58), and for Calorie Mate® of 200 kcal with water vs. isocaloric glucose solution they were 100 (93–108 90–120) vs. 105 (90–110 90–120) min (p = 0.54). The median (IQR range) for water was 40 (30–40 30–50) min. Energy content may be a critical determinant of the gastric emptying time when ingesting soluble solid diets with water.
•The characteristics of a prefilming airblast atomization was experimentally analyzed.•The effects of the prefilmer edge thickness on the spray characteristics were made clear.•The time variations of ...the total droplet surface area were experimentally analyzed.•The changes of the mean droplet diameter along the downstream location were analyzed.
The effects of prefilmer edge thickness on the spray characteristics of a prefilming airblast atomizer were experimentally investigated. The Sauter mean diameter (SMD), variation of the mean diameter with time, and droplet number density were experimentally measured for various prefilmer edge thicknesses and air velocities at various measurement points. The liquid flow rate was kept constant. The effect of prefilmer edge thickness on SMD was large in the primary atomization region, but small in the secondary atomization region. In the primary atomization region, with increasing edge thickness, the droplet size distribution became broader, the SMD dispersion increased, and the droplet number density dispersion decreased. In the secondary atomization region, the SMD dispersion in time was small for all prefilmer edge thicknesses. The effect of prefilmer edge thickness on droplet number density dispersion was small. For a large prefilmer edge thickness, the SMD and the total droplet surface area varied randomly with time, whereas the arithmetic mean surface area was almost constant over the whole sampling period.
The influence of the polymer matrix density, chemical cross-links in the interface, and geometrical defect in the carbon nanotubes (CNTs) on the CNT pull-out from polymer has been analyzed by the ...molecular dynamics simulation. The interfacial shear strength (ISS) has also been estimated with the change of total potential energy. In the simulation, the crystalline polyethylene matrix is set up in a hexagonal array with the polymer chains parallel to the CNT axis. First, we investigate the effect of the polymer matrix density on the ISS by changing the distance between the chains. Simulated results show that the ISS increases with the increase of matrix density. Next, we examine the cross-link effect on the ISS by adding polyethylene cross-links in the interface. Here, an energy based switching criterion addressing cross-links traveling on the CNT has been proposed. It is found that the presence of cross-links and the cross-link positions affect the ISS. Finally, pentagon–heptagon defect, which reduces the tensile strength of the CNT and has been experimentally observed by Hashimoto et al. Hashimoto A, Suenaga K, Gloter A, Urita K, Iijima S. Direct evidence for atomic defects in graphene layers. Nature 2004;430:870–3, has been addressed as a geometrical defect in the CNT. When cross-links are present between the CNT and the polymer, this defect reduces the ISS due to the improper connections of cross-links around this defective region.
The effect of fiber arrangement on transverse tensile failure in unidirectional carbon fiber reinforced composites with a strong fiber-matrix interface was studied using a unit-cell model that ...includes a continuum damage mechanics model. The simulated results indicated that tensile strength is lower when neighboring fibers are arrayed parallel to the loading direction than with other fiber arrangements. A shear band occurs between neighboring fibers, and the damage in the matrix propagates around the shear band when the interfacial normal stress (INS) is sufficiently high. Moreover, based on the observation of Hobbiebrunken et al., we reproduced the damage process in actual composites with a nonuniform fiber arrangement. The simulated results clarified that the region where neighboring fibers are arrayed parallel to the loading direction becomes the origin of the transverse failure in the composites. The cracking sites observed in the simulation are consistent with experimental results. Therefore, the matrix damage in the region where the fiber is arrayed parallel to the loading direction is a key factor in understanding transverse failure in unidirectional carbon fiber reinforced composites with a strong fiber/matrix interface.
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