Acoustic signature identification of damage and wear mechanisms in a steel/glass sliding contact

The tribological behavior of a steel/glass ball-on-flat contact was studied by synchronizing the friction measurements with an acoustic emission device and a vision system. The results highlight two distinct friction regimes identified with low and high friction values. Their transition is characterized by a modification of acoustic emission signals. In addition, two main damage and wear mechanisms are identified: the creation and propagation of Hertzian cracks visible on the glass surface and the constitution of an interfacial layer of debris. The different accommodation mechanisms, activated successively or simultaneously, are identified for acoustic emission frequencies between 300 and 700 kHz. Eventually, this approach allows a real-time wear mechanisms identification and gives better insights about acoustic emission signals in relation to tribological systems.

Who invented the glasses and when

Glasses, if to sort things out, are one of the most remarkable inventions of mankind, which has given millions of people the opportunity to perceive the world through vision. Prototype of the first glasses — they were the thinnest emerald plates enclosed in a bronze frame — was found in the tomb of Tutankhamun according to historical information. Ancient Greeks and Romans did not know the glasses unlike the ancient Egyptians and used pieces of rock crystal for reading, they preferred to use monocle prototypes, i.e., devices for one eye. Medieval monks also tried to use pieces of rock crystal or quartzite as lenses, which after some time they began to place in a frame. Arabs were the first to come up with a glass ball as an optical device. It is believed that glasses for the protection against the sun and sun glare were invented even earlier than glasses for vision correction. It is noteworthy that this invention belongs not to the southern, but to the northern peoples –inhabitants of Greenland were the first to come up with the use of bone plates with narrow slots that protected eyes from the snow shining in the bright sun.

High-Index Glass Ball Retroreflectors for Measuring Lateral Positions

This paper is concerned with backscattered luminous signals, coming from a particular class of dielectric spheres illuminated by a coherent source. The purpose is to measure the lateral position of the sphere serving as an optical target, to achieve an overall contactless sensor of lateral position in space. Traditional approaches and theories such as ray-tracing and Mie scattering—as implemented in dedicated software—are applied to investigate their fitness for purpose in this application. No previous literature was found dealing with this specific case. Unfortunately, our observations did not match the theories’ predictions to an acceptable degree, and these approaches proved to be unsatisfactory. The rest of the paper focusses then on the development and comparison of suitable algorithms to compute the image coordinates of a representative point, which was in fact the true motivation of this work. Two original algorithms are proposed and discussed. Their robustness and repeatability are benchmarked under noisy conditions and at different distances from the target, with simulated as well as real images. Both resulted capable of sub-pixel accuracy.

Tribological Properties of Double-Network Gels Substituted by Ionic Liquids

Since human body joints have a gel-like structure with low friction that persists for several decades, hydrogels have attracted much interest for developing low-friction materials. However, such advantages can hardly be realized in industrial usage because water in the gel evaporates easily and the gel deswells. The substitution of water with an ionic liquid (IL) is one of the effective ways to overcome this problem. In this study, we substituted water in a double network (DN) hydrogel with 3-ethyl-1-methyl-imidazolium ethylsulfate (EMI-EtSulf), a hydrophilic IL, via a simple solvent exchange method to obtain a DN ion gel. A compressive test and thermogravimetric analysis showed that the DN ion gel has a high compression fracture stress and improved thermal properties, with the difference in 10% loss of temperature being ΔT10 = 234 °C. A friction test conducted using a reciprocating tribometer showed that the friction of a glass ball/DN ion gel was relatively higher than that of a glass ball/DN hydrogel. Because the minimum coefficient of friction (COF) value increased after substitution, the increase in polymer adhesion caused by the electrostatic shielding of the surface moieties of glass and poly 2-acrylamidomethylpropanesulfonic acid (PAMPS) was considered the main contributor to the high friction. As the COF value decreased with increasing temperature, the DN ion gel can achieve low friction via the restriction of polymer adhesion at high temperatures, which is difficult in the DN hydrogel owing to drying.

Pemodelan perpindahan massa ekstraksi kolom isian dengan distribusi ukuran tetesan

Mass transfer modeling of extraction in a packed bed with droplet size distribution The evaluation of liquid extraction packed column is not able yet to give a satisfying result caused by constant spherical droplet size assumption. Droplet size from dispersion phase that is not homogeneous causes column calculation approach with assumption form of droplet haves the character of constant cannot be applied again. The goal of this research is to build droplet distribution model and mass transfer model at various heights of extraction column both in continuous phase and in dispersion phase. Droplet distribution model is more accurately applied to describe droplet breaks distribution for extraction in glass ball packed column with average of errors 4.53% compared to raschig ring packed column with average error of 11.52 %. At glass ball packing, the mass transfer modeling with total droplet has errors average to 57.67% while at raschig ring packing the model has errors average to 121.38%. Glass ball packing column model has smaller mean errors compared to raschig ring packing column because the glass ball packing form is more regular than the raschig ring packing. The amount of error between the mass transfer models and the experiment is caused by difference of the initial number of droplets that exit from the nozzle in the half circle column and in the full circle column. Keyword: extraction, packed column, droplet distribution model, mass transfer model AbstrakUkuran tetesan dari fasa dispersi yang tidak homogen menyebabkan pendekatan perhitungan kolom dengan asumsi bentuk tetesan bersifat konstan tidak dapat digunakan lagi. Tujuan dari penelitian ini adalah untuk membangun model distribusi tetesan dan model perpindahan massa pada berbagai ketinggian kolom ekstraksi baik di fasa kontinu maupun di fasa dispersi. Model distribusi tetesan lebih tepat digunakan untuk memodelkan fraksi tetesan pecah hasil penelitian pada ekstraksi kolom isian bola kaca dengan rata-rata error sebesar 4,53% dibandingkan dengan kolom isian raschig ring yang mempunyai error sebesar 11,52 Pada isian bola kaca pemodelan perpindahan massa dengan tetesan total mempunyai error rata-rata sebesar 57,67% sedangkan pada isian raschig ring mempunyai error rata-rata sebesar 121,38%. Model kolom isian bola kaca mempunyai error rata-rata yang lebih kecil dibandingkan dengan kolom kolom isian raschig ring, dikarenakan model isian bola kaca bentuknya lebih beraturan dibanding dengan kolom isian raschig ring yang bentuknya lebih tidak beraturan. Besarnya error perpindahan massa antara model dengan percobaan disebabkan oleh tidak samanya jumlah tetesan awal pada kolom setengah lingkaran dengan jumlah tetesan awal pada kolom lingkaran penuh.Kata kunci : ekstraksi,kolom isian, model distribusi tetesan, model perpindahan massa

Contact mechanics for polydimethylsiloxane: from liquid to solid

Adhesion between a glass ball and a polydimethylsiloxane (PDMS) sample is dependent on the PDMS cross-link density, and the transformation of the material from the uncrosslinked liquid state to the fully crosslinked solid state is investigated in this study.