Running-in of Rolling-Sliding Contacts

Running-in of two fresh and unworn surfaces in contact is a transient phase where friction and wear vary considerably in time. During running-in the surface properties of the components are adjusted. If the initial surface roughness of the rubbing surfaces is correctly chosen, the running-in changes into the steady-state phase. At this stage, the rubbing surfaces are in general smoother and their wear rate is low and constant. On the other hand, an inappropriate choice of roughness may lead to a rapid deterioration of the rubbing surfaces. The micro-geometry of the surface is an important factor in determining the life of mechanical components. During the running-in phase, the highest asperities are “flattened”, thereby increasing the number of asperities in contact and, as a result, increasing the load-carrying capacity of the surface.\ud Fundamental studies that attempt to consider the details of running-in phenomena are relatively rare. This research is conducted with the aim of exploring the running-in phase for the rolling, sliding and rolling-sliding contact. Finite element simulations are conducted to calculate the stress distributions for the three types of contact motions during the running-in phase. The evolution of the contact pressure for a certain rolling or sliding distance is studied to unravel the running-in phase.\ud During running-in of rolling contacts, the change in the surface topography results in the transformation from a rough surface to a smoother surface: the flattening of the high asperities induces a reduction in surface roughness. This flattening of asperities is due to plastic deformation and causes a higher equivalent residual stress at the surface. The transition of the running-in phase to the steady-state phase of a rolling contact is governed by the transition of plastic to elastic deformation on roughness level.\ud In sliding contacts, the proposed finite element (FE) model combined with the Archard wear equation successfully predicts the contact pressure evolution and change in the topography on a macroscopic point of view. The change in the topography in a sliding contact is mainly caused by wear. A new FE model, with respect to the artificial and real surface roughness, is discussed. It is found that the proposed model is a useful tool to study the running-in of a surface on roughness level.\ud The changes on macroscopic and on microscopic level of the surface are also discussed in the running-in of rolling-sliding contacts considering two aspects: wear and plastic deformation. The geometrical change of the contacting surface due to wear is predicted using the present FEM model, combined with the Archard wear equation, and has been compared with results from the literature. Calculations are performed to predict the wear of an artificial rough hemisphere in rolling-sliding contact with a smooth cylinder. The model also predicts the change of real rough surfaces which were in good agreement with the experimental results. The change of a rough surface, represented by an arithmetic average surface roughness, Ra, is predicted for lubricated rolling-sliding contacts using the load-sharing concept. The results obtained are in good agreement with experimental results.\ud A FEM based model has been developed to study the running-in of rolling, sliding and rolling-sliding contacts on macroscopic level as well as on roughness level. However, the transition between the running-in phase and the steady-state phase for sliding and rolling-sliding contacts cannot be determined by considering only one single parameter; likewise for the rolling contact situation. Wear is an ongoing process

Task and Kinematic Parameters for Upper Limb Stroke Patient: A Review

The development of robotics technology has now been used to assist the rehabilitation therapy process of stroke patients.  This far, the progress of therapy patients has been observed qualitatively and quantitatively with several clinical assessments such as Fuegl Meyer, Barthel Index, Motor Function Index, etc. This paper aims to provide a review of stroke patient progress evaluation measurements using kinematic parameters using elbow and shoulder robotic therapy devices and provide an overview of the types of exercises performed on the robotic therapy interface on the motor and cognitive development of stroke patients. Thirty publications that used kinematic parameters as the basis for assessing the development of stroke patients were included, there were 81 kinematic parameters from all the studies reviewed, based on ICF 53 of which were included in the Body Functions and Structures (BFS) classification, and 28 others were included in the Activities and Participation (AP) classification. Several studies showed a good correlation between the measurement of kinematic parameters and clinical assessment (P0.7; P<0.05)

Stick-slip behaviour of a viscoelastic flat sliding along a rigid indenter

The sliding contact of soft material surface due to a rigid indenter is different from metal and some other polymers. A stick-slip motion is more frequently obtained than a smooth motion. By modeling the soft material as low damping viscoelastic material, this study proposes an analytical model to identify the stick-slip behavior of sliding system. The sliding system is a fixed rigid indenter that slides against on a moving soft material surface. A stick-slip model is developed and the motion of the sliding system is assumed to be in a solely tangential direction. By implementing the simple coulomb friction law, an exact solution is presented in the case of no damping of the sliding system. Results show that the periodic displacement of the stick-slip model is strongly depending on the friction force, sliding velocity and material stiffness. Furthermore, the effect of a viscous damping and velocity-dependent friction on the behaviour of the sliding system are discussed

ANALISIS PENGARUH PEMBEBANAN TERHADAP TEGANGAN DALAM SAMBUNGAN TULANG PINGGUL BUATAN DENGAN METODE ELEMEN HINGGA

Pengetahuan letak dan besar tegangan maksimum akibat pembebanan dalam sistem sambungan tulang pinggul buatan merupakan hal yang penting untuk menjamin kualitas sambungan. Selain itu, sifat material pengganti komponen dan dimensi yang digunakan dalam sambungan secara umum dapat mempengaruhi kemampuan sambungan tulang pinggul buatan.Tujuan penelitian ini adalah mengembangkan model elemen hingga untuk menganalisa pengaruh pembebanan sebagai model berat beban pada manusia terhadap tegangan yang terjadi dalam sistem sambungan tulang pinggul buatan. Perangkat lunak berdasarkan metode elemen hingga, ANSYS digunakan untuk memodelkan berbagai lapisan komponen sambungan yang terbentuk dan sekaligus menghitung besarnya tegangan von Mises untuk mengetahui kegagalan yang mungkin terjadi. Berdasarkan studi ini, diketahui bahwa material viskoelastik berpengaruh terhadap distribusi tegangan yang terjadi pada tiap-tiap lapisan. Besarnya tegangan von Mises maksimum yang terjadi pada semua lapisan dalam sistem sambungan tulang pinggul buatan yang dikembangkan untuk femoral head dengan diameter 28 mm terbukti memenuhi persyaratan secara keteknisan karena tidak melebihi tegangan luluh material pembentuknya

Pemodelan Keausan Steady State : Analitik, FEA, dan Eksperimen

Kontak permukaan antara dua benda dalam permesinan sangat lazim terjadi. Kontak ini dapat mengakibatkan keausan. Para ilmuwan membagi tahapan keausan dalam hubungannya dengan umur pakai ada tiga macam, yaitu: running-in, steady state, dan wear out. Paper ini membahas tentang pemodelan keausan steady state. Pemodelan dibangun dengan model analitik dan pemodelan berbasis FEA. Model keausan secara analitik dikembangkan dari Model Archard. Pemodelan FEA dengan bantuan software ANSYS digunakan untuk memprediksi keausan pin pada simulasi pin-on-disc. Simulasi ini berupa kontak sliding yang dilakukan untuk mengetahui besarnya keausan yang terjadi pada pin. Untuk memvalidasi kedua model, eksperimen ball-on-disc juga dilakukan. Hasil pemodelan analitik dan FEA menunjukkan keausan mengalami peningkatan sangat signifikan pada tahap awal, kemudian mencapai kestabilan seiring dengan bertambahnya jarak sliding. Laju keausan mengalami penurunan yang sangat signifikan pada tahap running-in dan stabil pada fase steady state. Hasil eksperimen memperlihatkan permukaan telah konformal pada saat steady state. Ketiga present model menunjukkan hasil yang sangat baik dalam memprediksi keausan.Kata kunci:  “keausan”, “steady state”, “FEA”, “pin-on-disc”, “ball-on-disc”

Friction Reduction in Lubricated-MEMS with Complex Slip Surface Pattern

AbstractMany types of micro-electro-mechanical-system (MEMS) based products are currently employed in a variety of applications. However, high friction in these systems is a problem which limits the development of MEMS devices in which sliding contacts are involved. The aim of this research is to evaluate the effect of boundary slip on the hydrodynamic friction in a low load lubricated MEMS, in particular when boundary slip takes places in the certain region of the lubricated sliding contact, i.e. complex slip surface pattern. The effectiveness of the boundary slip in reducing friction is highlighted. The results indicate that the deterministic complex slip pattern has a beneficial effect on decreasing friction

Development of Low Cost Supernumerary Robotic Fingers as an Assistive Device

This paper presents the development of new type of wearable robot namely Supernumerary Robotic Finger (SRF) as  an  assistive   robot  for  healthy  people  or  people   with hemiparesis or hemiplegia. SRF comprises of two manipulators attached  in user’s wrist. Three flex sensors are utilized to measure the finger bending of the user’s finger. The posture of SRF is driven by modified glove sensor. The kinematics of both robotic thumb (RT) and robotic finger (RF) is studied using D-H parameter method and RoboAnalyzer software in order to understand the kinematic behavior of this robot. Each of RT and RF has three degrees of freedom (DOF). The posture of RT and RF is controlled using bending angles of thumb and finger from the user that are read by flex sensor. Based on the experimental results for people with healthy hand, the proposed SRF can assist object manipulation task in grasping, holding, and manipulating an object by using single hand when normally it only can be done by using two hands. From the experimental results on a person with healthy hand, the proposed of SRF can be employed as an assistive device for people with hemiparesis or hemiplegia. This device will enable people with diminished hand function work more independently