Crack breathing as a function of crack location under the effect of unbalance force

In this work, an analytical model was developed to investigate the dependence of crack breathing behavior on the crack location under the effect of unbalance force. A parameter known as the effectual bending angle is introduced to describe the non-linear relationship between crack direction and bending direction for balanced and unbalanced shaft along the shaft length. Breathing behavior of crack was visualized by examining the duration of each crack status (open, closed and partially open/closed) during a full shaft rotation. It is shown that a crack in an unbalanced shaft has more breathing patterns than a crack in a balanced shaft, including single status (fully open/never-closed or fully closed/never-open) and dual statuses. Two pairs of interesting locations along the shaft length were identified, where the crack shows specific breathing behaviours. Further, the angular range during which a crack remains fully closed, partially open/closed or fully open, changes significantly with the crack location. The analytical model developed in this work can be further utilised to obtain the time-varying stiffness matrix of the cracked shaft element under the influence of unbalance force

Effective teaching method for engineering education from student's perspective

Education system involves two primary complementary processes: learning and teaching. A successful implementation of this system depends on synchronisation of these two processes. One the receiving end, students learns by utilizing different mediums such as hearing and seeing and by applying different methods such as memorizing, visualizing or logically understanding. One the delivering ends, teachers instruct by utilizing different approaches: visual or auditory, face-to-face or online, theoretical delivery or practical demonstration and so on. In complex subjects such as of engineering education, mismatch often exists in the system between the receiving and delivering point of instruction. As a result, majority of students have performed poorly in examination, students get discouraged about the course, and themselves, and in some case change to other curricula or drop out of school. Academics know something is not working or begin to wonder if they are in the right profession. Most seriously, society loses potentially excellent engineers. However, promising future can be speculated on the minimisation of this gap as extensive research, workshop and conferences are in place to improve the education system. Still, only few can be found that specifically focuses on improving technical education system such as engineering which is very important as graduates from this school are expected to make significantly sensitive decisions to the community such as designing of bridges, maintaining electricity production or ensuring reliable water supply. In this paper, some effective alternatives teaching methods particularly significant in engineering education and which teaching methods are preferred by most engineering students are discussed from student’s perspective. The suggested teaching style will improve the quality of teaching and that will be effective for students and comfortable for the professor will evolve naturally and relatively painlessly, with a potentially dramatic effect on the quality of learning that subsequently occurs

Tribological performance of hydrogenated amorphous carbon (a-C: H) DLC coating when lubricated with biodegradable vegetal canola oil

Increasing environmental awareness and demands for lowering energy consumptions are strong driving forces behind the development of the vehicles of tomorrow. Without the advances of lubricant chemistry and adequate lubricant formulation, expansion of modern engines would not have been possible. Considering environmental awareness factors as compared to mineral oils, vegetal oil based biolubricants are renewable, biodegradable, non-toxic and have a least amount of greenhouse gases. Furthermore, improvement in engine performance and transmission components, which were impossible to achieve by applying only lubricants design, is now possible through diamond like carbon (DLC) coatings. DLC coatings exhibit brilliant tribological properties, such as good wear resistance and low friction. In this regard, tribological performance of a-C: H DLC coating when lubricated with Canola vegetal oil has been investigated by the help of a ball-on-flat geometry. Experimental results demonstrated that the a-C: H DLC coating exhibited better performance with Canola oil in terms of friction and wear as compared to the uncoated materials. Large amount of polar components in the Canola oil significantly improved the tribological properties of the a-C:H coating. Thus, usage of a-C: H DLC coating with Canola oil in the long run may have a positive impact on engine life

Influences of angular position of unbalanced force on crack breathing mechanism

In this study, a new mathematical model is developed to study crack breathing behaviours considering effect of angular position of unbalanced force at different crack locations. Crack breathing behaviours are determined by using effectual bending angle and studying the transient change of the crack area. Different crack breathing behaviours of the unbalanced shaft are observed for different combinations of angular position of unbalanced force with crack location, except for two crack locations at 0.3 L and 0.8335 L, in which L is the total length of the shaft, where unbalanced shaft behaves completely like a balanced shaft. Based on different combinations of angular position of unbalanced force with crack location, the stiffness of unbalanced shaft varies accordingly. An unbalanced shaft is stiffer than a balanced shaft when angular position of unbalance force is between 90° to 270° and crack located between 0.3 L and 0.8335 L and it is flexible when the crack is located outside of this crack region. On the other hand, it is flexible when angular position of unbalanced force is between 0° and 90° or 270° to 360° and the crack is located in the middle region and it is stiffer when the crack is located outside of this crack region

Dependence of shaft stiffness on the crack location

In this study, an analytical model is developed to study crack breathing behavior under the effect of crack location and unbalance force. Crack breathing behavior is determined using effectual bending angle by studying the transient change in closed area of the crack. The status of the crack of a balanced shaft is symmetrical about shaft rotational angle and the duration of each crack status remains unchanged. The global stiffness of the balanced shaft is independent of crack location. Different crack breathing behavior for the unbalanced shaft has been observed. The influence of crack location on the unbalanced shaft stiffness can be divided into three regions. When the crack is located between 0.3L and 0.8335L, where L is the total length of the shaft, the unbalanced shaft is less stiff and when located outside this region it is stiffer than the balanced shaft. It was also found that unbalanced shaft stiffness has a maximum value with a crack at 0.1946L, a minimum value at 0.8053L and same value as balanced shaft at 0.3L and 0.8335L

Location dependence of breathing mechanism for a slant crack in a shaft

Periodic stresses are always imposed on a rotor, and thus, a crack due to fatigue is unavoidable. Machinery must be properly diagnosed to avoid tragic accidents. Vibration detection is the most important tool for such a diagnosis system. It is important to know the vibration characteristics of a cracked rotor in order to develop a monitoring system which can detect a crack in an early stage of propagation. In this study, to explore the crack breathing mechanism, a three-dimensional finite element model is simulated by using a commercial analysis solver—Abaqus/Standard. A two-disc rotor system with a slant crack is used under the coupling effect of rotor weight and unbalance force. Unlike crack breathing under rotor weight-only, a crack opens and closes differently under the effects of unbalance forces. Crack breathing depends on its location along the length of the shaft and individual parameters of the rotor system. A few crack locations are recognised along shaft length where the crack may stay fully closed or open during shaft rotation under certain loading circumstances. These locations also split the shaft into different areas based on the orientation of the unbalance force, crack size and location, where shaft stiffness may be higher or lower. Presented findings indicate that predicting the dynamic response of cracked rotors can be anticipated much accurately. Therefore, the impacts of unbalance forces and individual rotor physical characteristics on crack breathing must be taking into consideration

Effect of unbalance force on the crack breathing mechanism

The dependence of crack breathing behavior on the crack location was investigated under the effect of unbalance force. A parameter known as the effectual bending angle is introduced to describe the non-linear relationship between crack direction and bending direction for balanced and unbalanced shaft along the shaft length. Breathing behavior of crack was visualized by examining the duration of each crack status (open, closed and partially open/closed) during a full shaft rotation. It is shown that a crack in an unbalanced shaft has more breathing patterns than a crack in a balanced shaft, including single status (fully open/never closed or fully closed/never open) and dual statuses. Two pairs of interesting locations along the shaft length were identified, where the crack shows specific breathing behaviors. Further, the angular range during which a crack remains fully closed, partially open/closed or fully open, changes significantly with the crack location. The analytical model developed in this work can be further utilized to obtain the time-varying stiffness matrix of the cracked shaft element under the influence of unbalance force

New crack breathing mechanism under the influence of unbalance force

In this paper, a new analytical model (unbalanced one), which considers the coupling effects of unbalance force, rotor weight, and rotor physical and dimensional properties, is developed to study the actual breathing mechanisms of the transverse fatigue crack in a cracked rotor system. The results are also compared with those of the existing balanced model, where only rotor weight is considered. It has been identified that a crack in the unbalanced model breathes differently from the one in the balanced model. A crack’s breathing mechanism in the unbalanced model depends strongly on its location along shaft length. At some special locations, a crack in the unbalanced model may remain fully closed or open during the shaft rotation, which will never occur in a balanced model. It may also behave completely like the one in the balanced shaft. Depending on the crack location, unbalance force magnitude and orientation, the unbalanced shaft may be stiffer or more flexible than the balanced counterpart. It is also demonstrated that the unbalanced model will progressively approach balanced one as unbalance force decreases. Further, different crack breathing mechanisms between two models lead to a large difference along shaft length in the second area moment of inertia, which forms the elements of local stiffness matrix at crack location. It is expected that more accurate prediction of the vibration response of a cracked rotor can be achieved when the effect of unbalance force and rotor properties on the crack breathing has been taken into account

Tribological characteristics of amorphous hydrogenated DLC in the presence of commercial lubricating oil

Currently diamond like carbon (DLC) coatings application for automotive components is becoming a favorable strategy to cope with new challenges faced by automotive industries. DLC coating is very effective to lower the coefficient of friction and wear rate, which in turn could improve fuel efficiency and durability of the engine components. Commercially available fully formulated lubricating oils are specially produced to enhance the lubrication of ferrous materials. Therefore, nonferrous coating (DLC) interaction with commercial lubricating oil needs to be investigated. In this current investigation, coefficient of friction and wear rate were investigated by ball on plate tribo testing machine at different temperatures in the presence of SAE 40 lubricating oil. At high test temperature coefficient of friction decreases, however wear rate increases for the a-C:H coated plate, and steel/steel contact shows opposite trend of coefficient of friction and wear rate change

Tribological characteristics of diamond like carbon coating in the presence of environment friendly vegetable based oils

Nowadays environmental awareness issue draws the attention of the scientists; lubricant industry also focuses on environment friendly lubricating oils. Therefore, vegetable oils draw the attention of scientists because of environmental friendly as well as good lubricating characteristics. However, good lubricating vegetable oils often shows inferior property because of low thermal stability, hence, to enhance the performance of vegetable oils self-lubricating diamond like carbon coating is considered, which helps in lowering the friction force which in turn lower friction induced heating, as a result stability of vegetable oils increases. In this current research, three vegetable based oils (sunflower, palm, coconut) are considered as lubricating oil. Tribological tests are conducted by ball on plate tribo-testing machine, tetrahedral type diamond like carbon coated plates and uncoated balls are used in the tribo-pair. Among the testing conditions sunflower oil shows good friction and wear characteristics and coconut oil shows inferior friction and wear characteristics