Evaluation of thermal control performance of phase change materials for thermal shock protection of electronics

Phase change materials have important application value in the fields of heat storage, cold storage, and thermal shock protection of electronic chips. In particular, in the field of chip thermal shock protection, phase change materials can use the solid-liquid phase change process to absorb a large amount of latent heat, thereby suppressing the temperature rise of the chip and preventing it from overheating. At present, there are mainly three types of common phase change materials: organic, inorganic and metallic phase change materials. There exists significant difference in the thermophysical properties of the three types of materials, and their thermal control performance also have their own characteristics. This paper sorts out the main thermophysical data of the three types of phase change materials. Through theoretical modeling and analysis, the thermal control performance of these materials is quantitatively evaluated and compared. For typical chip thermal shock conditions, the three types of phase change materials are compared, and their typical characteristics are intuitively displayed. The research results can serve as value reference for the development of phase change thermal control technology for chips.

Susceptibility of Impact Damage to Whole Apples Packaged Inside Molded Fiber and Expanded Polystyrene Trays

Postharvest damage, leading to loss and waste, continues to be a significant problem in the fresh produce industry. Trays, designed to reduce fruit-to-fruit contact, are utilized by the apple industry to minimize bruising of whole apples. During distribution, packaged apples are subjected to various supply chain hazards, which may lead to bruising damage. Currently, molded fiber (MF) and expanded polystyrene (EPS) trays transport whole apples from the packhouse to the retail outlet. Mechanical shock, by free-fall drop method, was used to evaluate the performance differences between the two trays and quantify the bruising characteristics of the apples. Results showed that the EPS trays provided better shock protection to the apple as compared to the MF tray, reducing the impact acceleration by more than 70%. Additionally, the bruise susceptibility was 40% less for the apples packaged inside the EPS trays, regardless of drop height. However, apples packaged in the middle layer trays were most susceptible to bruising damage, regardless of tray type.

Advances in Projectile Penetration Mechanism in Soil Media

The penetration to geological shield occurs in many situations at various velocities and scales, for example, meteor-cratering, pile driving, falling of objects from high-rise building construction, and debris/fragments from failed components. The soil media is an efficient energy dissipation system and effective shock protection shield. Impact circumstances are currently getting widespread attention. A lot of research has been done on soil media for impact and penetration. The phenomenon of dynamic penetration in heterogeneous particulate soil medium is very complex and the target soil media under dynamic impact especially under high speed and deep penetration neither behave completely as solid nor as liquid. The topics of recent research interest in the field of penetration to soil media and their significant findings are critically reviewed in the present study. The dedicated review of analytical, empirical, experimental, and computational methods to predict the response of soils media-impacting objects to penetration is presented. The emerging challenges in fundamental research of penetration into soil media are outlined and it is an attempt to formulate the future research directions in the field of soil media penetration.

УРАВНЕНИЯ ПРОСТРАНСТВЕННОГО ДВИЖЕНИЯ ТВЕРДОГО ТЕЛА С ПОДАТЛИВЫМ КРЕПЛЕНИЕМ К ФУНДАМЕНТУ (ЗАДАЧА АМОРТИЗАЦИИ В ПРОСТРАНСТВЕ)

The task of fastening equipment, especially ship equipment, is considered important in conditions of vibration and shock. Equipment can be mounted on shock absorbers. These shock absorbers solve the problems of vibration isolation and shock protection. The classic case is the use of rubber-metal shock absorbers. The equipment can be attached to the foundation with bolts and dowels. In this case, the bolts mustn't collapse and the joints do not open during shock. An interesting case is an attachment, the fastening of which should not be destroyed. Attachments are usually attached by bolts, the destruction of which is not permissible. In the case of plastic deformation of the bolts they can be tightened, and then replacing the collapsed shock absorber is not easy. The condition of the fastening devices can be investigated by modeling, using computer technology, the movement of the unit. The use of computer technology is justified by the cumbersomeness of the task, the nonlinear characteristics of rubber-metal shock absorbers, and bolts in the case of plastic deformations. Typically, when modeling the movement of shock-absorbing equipment, they are limited to a flat task or a case of hard keys. To solve the spatial problem, we introduce three coordinate systems. One system is non-mobile and connected to the foundation. Two other coordinate systems have a beginning at the center of gravity of the unit. The axes of one of these systems are parallel to the axes of the system associated with the foundation. And the other of these systems are rigidly connected to the unit. At the initial moment, in case of rest, all three systems coincide. For the general case of motion, Euler angles can be used, but due to the small movements of the equipment, accuracy is lost. Indeed, the intersection line of the planes determining the Euler angles is determined with an error (the case of almost parallel planes). To solve this problem, the authors used the angles between the axes associated with the equipment and the foundation plane. Then, through these angles, Euler angles were expressed and expressions were obtained that allow the use of numerical methods to solve the equations of motion.

Ground Leakage Current Caused by Common-Mode Voltage of PWM inverter

In railway tractive vehicles, three-phase PWM (Pulse Width Modulation) inverters generate parasitic Differential-Mode Voltages (DMV) and Common-Mode Voltages (CMV). Parasitic voltages are a side effect of using the width modulation to shape the phase-to-phase inverter’s voltage. In this article, the authors present a mathematical description of the DM and CM voltages and carry out their spectral analysis. Based on the spectral harmonics analysis, the authors present a method for filtration of harmonics of DM and CM voltages aimed at limiting the capacitance parasitic currents: due to DM voltage – phase-to-phase parasitic current and CM voltage – ground parasitic currents. As the final result of the tests, almost complete elimination of leakage parasitic current form PE shock protection system was achieved.

Graphynes: an alternative lightweight solution for shock protection

The excellent mechanical properties of graphyne (GY) have made it an appealing candidate in the field of impact protection. We assessed the deformation mechanisms of monolayer GY nanosheets of different morphologies, including α-GY, β-GY, γ-GY and 6612-GY, under supersonic-velocity impacts (from 1 to 6 km/s) based on in silico studies. Generally, cracks initiate at the geometry center and the nanosheet experiences significant out-of-plane deformation before the propagation of cracks. Tracking the atomic von Mises stress distribution, it is found that its cumulative density function has a strong correlation with the magnitude of the Young’s modulus of the GYs. For nanosheets with a higher Young’s modulus, it tends to transfer momentum at a faster rate. Thus, a better energy dissipation or delocalization is expected during impact. This study provides a fundamental understanding of the deformation and penetration mechanisms of monolayer GY nanosheets under impact, which is crucial in order to facilitate their emerging applications for impact protection.

Foreign Exchange Reserves as a Shock Protection – the Example of Bosnia and Herzegovina

Significant increase in foreign exchange reserves in recent decades, including the period of the global financial crisis of 2008 and 2009, has intensified research on the importance and role of foreign exchange reserves and their adequate level. Although the financial crisis has emphasised the importance of maintaining an adequate level of foreign exchange reserves, there is insufficient consensus on the level of foreign exchange reserves that should be maintained in the event of crises and shocks.This paper explores foreign exchange reserves of Bosnia and Herzegovina and their adequate level over the period from 2005 to 2015 as well as in the event of a shock which can be generated by internal or external factors.The aim of this paper is to examine whether foreign exchange reserves of Bosnia and Herzegovina were sufficient in the observed period as well as in the event of shocks that national economy could be exposed to.For the research purposes, comparative method and the application of sensitivity analysis and scenarios were used to analyse and evaluate the adequacy of foreign exchange reserves of Bosnia and Herzegovina. The final results demonstrate thatduring the observed period foreign exchange reserves of Bosnia and Herzegovinawere adequate. However, in the case of extreme shocks Bosnia and Herzegovinadoes not possess the sufficient level of foreign exchange reserves. Such findings recommendto the Central Bank of Bosnia and Herzegovina, together with other economicpolicies, additional efforts to accumulate foreign exchange reserves in themedium term.