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The present work focuses on the friction coefficient for various geotextile sandbag structures especially dikes under different conditions. Based on the review of existing investigations there are several gaps to close. Former investigations do not include the whole scope of needed surfaces and conditions. Especially the friction coefficients for polypropylene and even for jute as material mainly used for small geotextile sandbags are not fully available. Additionally, the influence of the surface moisture is not consequently investigated, particularly for jute. Due to this, eleven test series (three with sandbag on sandbag configuration and eight with sandbag on ground surface) with 780 single readings are finalized. In comparison to former studies there are results for surface combinations of good harmonization and those with differences. A comparison of the earlier studies already shows different results Summarized it can be stated that the presented results are representative friction coefficients for calculation of realistic sandbag structures e. g., sandbag dikes or spring cascades. [ABSTRACT FROM AUTHOR]

Plants such as Galium aparine show directional gripping to various surfaces because of their microscale hook structures. A bio‐inspired artificial version of microhooks holds potential as a bidirectional, reversible, and reusable dry adhesive for soft, wet, or fibrous substrates such as skin or textiles. However, current methods for fabricating 3D structures are often costly, time‐consuming, or require precise alignment steps. Herein, a facile, cost‐effective, scalable, and unconventional microfabrication technique is proposed using tilted photolithography on a rotary stage and shear molding to fabricate a soft polydimethylsiloxane polymer mold containing the inverse replica of directional microneedle structures. To demonstrate the proof‐of‐concept, polyurethane is then added to the mold to obtain directional microneedles, referred to as microhooks. Friction force measurements using a nanotribometer show anisotropic performance (strong attachment in one direction and easy detachment in the opposite direction over multiple cycles) similar to the natural microhooks. Tribological characterization of the microhooks shows a gripping force 2.25 times greater than the sliding force. The fabricated microhook structures also provide an adhesion force of ≈0.62 N cm−2 to artificial skin. This biomimetic approach promises precise adhesion control and material versatility for attaching wearable devices and patches to the skin in biomedical applications. [ABSTRACT FROM AUTHOR]

Two stress regime‐dependent creep constitutive equations, that is, two‐regime Norton (2RN) model and Sin‐hyperbolic (Sinh) model, are adopted to numerically investigate the influence of constitutive equation and friction on the measurement of steady‐state creep strain rate based on five types small specimens. Results show that the influence of constitutive equation and friction depends strongly on the type of small specimen. A measurement error of more than 19 times may occur if the 2RN model is used, while the use of the Sinh model is able to generate a consistently lower measurement error. Of all small specimens, the cantilever beam testing (CaBT) is revealed to exhibit the best comprehensive performance in terms of measurement error and response to friction. To validate numerical findings, creep tests on the CaBT specimen of P91 steel are conducted at 600°C. Finally, recommendations on the choice of small specimen for obtaining creep strain rate are made. Highlights: Sinh model is better in describing stress regime‐dependent creep behavior.Influence of friction is strongly dependent on the type of small specimen.Small cantilever beam testing has the best comprehensive performance.Attention should be paid to selecting the constitutive equation and specimen type. [ABSTRACT FROM AUTHOR]

Controlling the wetting and spreading of microdroplets is key to technologies such as microfluidics, ink‐jet printing, and surface coating. Contact angle goniometry is commonly used to characterize surface wetting by droplets, but the technique is ill‐suited for high contact angles close to 180° $180^\circ $. Here, we attach a micrometric‐sized droplet to an atomic force microscope cantilever to directly quantify droplet–solid friction on different surfaces (superhydrophobic and underwater superoleophobic) with sub‐nanonewton force resolutions. We demonstrate the versatility of our approach by performing friction measurements using different liquids (water and oil droplets) and under different ambient environments (in air and underwater). Finally, we show that underwater superoleophobic surfaces can be qualitatively different from superhydrophobic surfaces: droplet–solid friction is highly sensitive to droplet speeds for the former but not for the latter surface. [ABSTRACT FROM AUTHOR]