A key capability of focused ion beam (FIB) tools is the ability to deposit conductive materials by introducing organometallic precursors such as tungsten hexacarbonyl [W(CO)6] or (methylcyclopentadienl) trimethyl plat...
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Nearly all species of modern birds are capable of flight;therefore mechanical competency of appendages and the rigidity of their skeletal system should be optimized. Birds have developed extremely lightweight skeletal...
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ISBN:
(纸本)9781118771396
Nearly all species of modern birds are capable of flight;therefore mechanical competency of appendages and the rigidity of their skeletal system should be optimized. Birds have developed extremely lightweight skeletal systems that help aid in the generation of lift and thrust forces as well as helping them maintain flight over, in many cases, extended periods of time. The humerus and ulna of different species of birds (flapping, flapping/soaring, flapping/gliding, and non-flying) have been analyzed by optical microscopy and mechanical testing. The reinforcing structures found within bones vary from species to species, depending on how a particular species utilizes its wings. Interestingly, reinforcing ridges and struts have been found within certain sections of the bones of flapping/soaring and flapping/gliding birds (vulture and sea gull), while the bones from the flapping bird (raven) and non-flying bird (domestic duck) did not have supporting structures of any kind. The presence of these reinforcing structures increases the resistance to torsion and flexure with a minimum weight penalty, and is therefore of importance in flapping/gliding birds. Vickers hardness testing was performed on the compact section of the bones of all bird species. The data from the mechanical testing were compared with microstructural observations to determine the relevance behind the reinforcing structures and its mechanical and biological role. Finite element analysis was used to model the mechanical response of vulture ulna in torsion.
This paper presents a workplace ergonomic study in a high-end server manufacturing environment to assess ergonomics risks and enhance the Lean transformation. Operators perform heavy and repetitive lifting and movemen...
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ISBN:
(纸本)9780983762430
This paper presents a workplace ergonomic study in a high-end server manufacturing environment to assess ergonomics risks and enhance the Lean transformation. Operators perform heavy and repetitive lifting and movement of products could place stress on their back and upper extremities. Forceful exertions to move a manual forklift in the workplace area could lead to fatigue and possible damage to muscles and other tissues. The objective of this study is to reduce ergonomics risks to an acceptable level and provide operators with the right tools and proper work environment. Digital human modeling based on the Jack software, is used for risk assessment. Results are analyzed to provide proper solutions. Ergonomic risks assessed include: force and posture risks, noise, vibration, temperature, and illumination. Lean process is implemented in the workplace to reduce the Lean wastes that include waiting time, transportation, and non-value-add processes. Ergonomic improvements are introduced to complement and support the Lean process implementation. Three main ergonomic risks are found to be high and could affect the operators: energy expenditure, posture, and back force. Several modifications are implemented to reduce these risks: the manual forklift is replaced with an automated forklift that is easy to move and requires less human effort, the workplace area is expanded to provide more work space, and the operators are provided with proper tools to perform the task without risk.
This paper presents a study that integrates lean manufacturing and ergonomic principles to redesign and improve the internal transportation process in a high-end server manufacturing environment. Transportation of ele...
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ISBN:
(纸本)9780983762430
This paper presents a study that integrates lean manufacturing and ergonomic principles to redesign and improve the internal transportation process in a high-end server manufacturing environment. Transportation of electronic parts within the factories is an important issue. The current transportation carts present quality hazards to electronic parts and they were not designed to handle the right dimensions and quantities of the newly introduced products. Furthermore, the current flow of carts introduces waiting time for the carts in the assembly areas. Inefficient transportation not only increases the waiting times but also the transportation costs. The objective of this study is to improve the transportation process and redesign transportation carts that are currently used to transport parts between different areas in a high-end server manufacturing environment utilizing lean and ergonomic principles. A new lean-based flow of transportation carts is proposed to reduce the waiting time and transported distance by having separate carts for each area. The new design of the carts represents a Poke-Yoke that prevents the operators from stacking the cards. Ergonomic principles are also considered in the new design. The number of carts required is estimated based on historical demand, outcomes from containment actions, current processes, and inputs from the production-planning department. The new lean-based flow and design of carts have resulted in cost savings and cost avoidance.
The microstructure and flow stress of the Mg-12Gd-3Y-0.5Zr magnesium alloy was investigated by compression test at temperatures ranging from 350 to 500 ~C and the strain rates ranging from 0.01 to 20 s-1. The flow str...
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The microstructure and flow stress of the Mg-12Gd-3Y-0.5Zr magnesium alloy was investigated by compression test at temperatures ranging from 350 to 500 ~C and the strain rates ranging from 0.01 to 20 s-1. The flow stress of the magnesium alloy increased with strain rate and decreased with deformation temperature. Flow stress can be expressed in terms of the Zener-Hollomon parameter Z, which describes the combined influence of the strain rate and temperature using an Arrhenius *** values of the deformation activation energy were estimated to be 245.9 and 171.5 kJ/mol at deformation temperatures below 400 ℃ and above 400 ℃, respectively. Two constitutive equations were developed to quantify the effect of the deformation conditions on the flow stress of the magnesium alloy. The effects of deformation temperature and strain rate on the microstriucture of the magnesium alloy were also examined and quantified by measuring the volume fraction of dYnahaically recrystallized grain Xd. Xd increased with increasing of deformation temperature. When the deformation temperature was below 475 ℃, X4 decreased with strain rate until it reached 0.15 s-1, then it increased again. When the deformation temperature was above 475 ℃, X4 increased with strain rate.
Lamb wave tomography (LWT) is a potential and efficient technique for non-destructive tomographic reconstruction of damage images in structural components or materials. A two-stage inverse algorithm proposed by the au...
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The crystallization of organic semiconductor thin films from an amorphous phase often results in a broad range of microstructures and molecular arrangements that in turn critically impact the electronic properties of ...
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The crystallization of organic semiconductor thin films from an amorphous phase often results in a broad range of microstructures and molecular arrangements that in turn critically impact the electronic properties of the film. Here we present a diffuse-interface model of thin film crystallization that accounts for out-of-plane tilting of the kinetically favored crystalline orientation as well as the simultaneous appearance of multiple polymorphs. By adjusting the relative thermodynamic stability of grains oriented with the fast-growing axis either parallel or perpendicular to the substrate, crystallization can be made to occur in the form of either commonly observed spherulites or more complex morphologies such as sectors and centers. Furthermore, tuning the relative kinetic coefficients and free energies of multiple polymorphs can result in a spherulite of one crystal structure embedded within a spherulite of another crystal structure. A parametric study of the effects of anisotropy, densification, time-varying treatments, and substrate patterning reveals a wide variety of morphologies that are possible in these thin films, driven by a combination of kinetic and thermodynamics effects.
We report on recent investigations into the mechanical properties of metallic micro-specimens deformed in tension and compression. We will focus on investigations using a custom test apparatus for in-situ focused ion ...
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