Joint Design Parameters Research Articles

Magnetic flux distributions in transformer core joints

This paper presents results of a rigorous analytical study performed in order to understand the role which joints play in determining the performance of cores of power and distribution transformers. The paper presents the details of the magnetic flux distribution and redistribution in the core joint region along the core stack height direction as a function of the operating flux density, core joint material, joint configuration, and joint design parameters. The results are presented for both conventional and step-lap joints. The results illustrate the benefits of the step-lap joint in reducing core losses, noise and excitation current. The results also explain the impact of overlap length, the number of laminations per step, and the contribution of the joint region to the whole core performance. The calculated flux density wave shapes in the joint region were found to be in good agreement with measured wave shapes. The results presented in this paper have been used in developing an accurate calculation of core losses for both power and distribution transformers. They have also been used to arrive at the optimum core joint configuration for a transformer core.

Study of Load Transfer Parameter in AASHTO Design Guide for Concrete Pavement

Some of the design parameters in AASHTO’s Guide for Design of Pavement Structures require experienced engineering judgment to obtain adequate designs. The load transfer parameter for concrete pavements in the AASHTO Guide is reviewed. A set of equations was developed to assist in choosing a J-factor for various pavement conditions. With three-dimensional finite element analysis, factorial runs were conducted to find the relationships between the critical stresses and joint design parameters—that is, joint width, diameter, length, and spacing of dowel bars. Extended procedures that incorporate dowel parameters into the J-factor were proposed. Conclusions were made to clarify the load transfer concept in the current AASHTO Guide and the effects of joint parameters on pavement performance.

Maximizing Solder Joint Reliability Through Optimal Shape Design

The automated search techniques from the field of numerical optimization provide tools that enable optimal design of electronic packages in general, and solder joints in particular. However, there is considerable difficulty in using these procedures for solder joints since the estimation of fatigue life is computationally very expensive. In this paper, global approximation schemes based on designed experiments, linear regression models, and artificial neural network models are developed to approximate the fatigue life as a function of solder joint design parameters. Since these approximate surfaces are inexpensive to evaluate, their use with the numerical optimization techniques leads to a computationally efficient method for optimizing electronic packages. The developed techniques are demonstrated using the 225 I/O Plastic Ball Grid Array (PBGA) package, manufactured by Motorola, Inc. An exact optimization of the solder joints (without approximations) is also carried out and used as a basis for comparing the accuracy and efficiency of the developed methods.

The Nature of Centroidal Locus in Misaligned Flip-Chip Solder Joints

The self-alignment mechanism of molten flip-chip solder joints is being increasingly used in passive alignment of optoelectronic devices. For these applications, three-dimensional models of misaligned solder joints are necessary to understand the effect of solder joint design parameters on self alignment. To reduce the complexity of fully three-dimensional models, intuitively reasonable assumptions are often made in their theoretical development. Two such assumptions for misaligned flip-chip solder joints with circular pads are that the locus of centroids is a straight line and that the cross sections are circular in shape. In the present paper, the limits of validity of these two assumptions are explored. In general, if either the top and bottom pad radii are identical, or if there is no misalignment between the pads, then the centroidal locus is a straight line and the cross sections are circular. The extent of deviation from straight line centroidal locus or circular cross section depends on the ratio of the top and bottom pad radii and on the extent of misalignment between the pads. For a misalignment equal to 20 percent of the solder joint height and a joint with 90 percent pad diameter ratio, the deviation from straight line locus is 7 percent and the deviation from circularity is less than 1 percent. However, as the pad ratio is decreased to 50 percent, and as the misalignment is increased to 100 percent, the deviation in centroidal locus increases to 43 percent and the deviation from circularity increases to 33 percent. Thus, straight line locus and circular cross sections are reasonable assumptions for flip-chip solder joints provided the pad diameter ratio and misalignment are small.

Design of solder joints for self-aligned optoelectronic assemblies

Self-aligning soldering is the critical technology for precision optoelectronic assembly. The pre-assembly solder joint design can improve the final alignment accuracy. In this paper, a public domain software Surface Evolver is modified as a modeling tool for the design of solder joints for self-aligned assemblies. Furthermore, for convenient and efficient design, the results from the numerical model are nondimensionalized and regressed as a polynomial regression model, which describes the relationships between the surface tension forces and the solder joint design parameters explicitly. The regression model is established based on 1100 data points calculated for solder joints with circular pads. We apply this model tool to several design case studies, including the joint array design for self-alignment and the solder assembly of a FLC/VLSI spatial light modulator. It is demonstrated that the model developed here is a very powerful and convenient tool to aid in the design of solder joints for various applications. >

An algorithm for the determination of optimal design parameters of joint [formula omitted] and [formula omitted] control charts

This paper presents a simplified algorithm for the determination of optimal design parameters of joint X and R control charts. Numerical examples show that the algorithm is accurate, efficient, and overcomes drawbacks of the previous algorithm.

Strength and damage content of sectional glass shells with different types of dismantable joints

1. A study was made of the structural strength of inorganic glass in sectional spherical and cylindrical shells with new types of dismantable mechanical joints under conditions of external hydrostatic pressure. It was found that the choice of joint design and processing parameters on the basis of study of the effect of these parameters on the stress-strain state of the shell makes it possible to create a favorable stress state in the glass element so as to significantly increase and stabilize the maximum load-carrying capacity, endurance, and durability of the structure. 2. Sectional shells with dismantable joints realized by joining glass elements end to end showed satisfactory resistance to fracture under brief one-time and long-time applications of hydrostatic pressure but low resistance under pulsating loads, thus limiting the use of such a joint. 3. Designs in which glass bears directly against metal in the joint should be used only for brief one-time loading with external pressure: such a joint does not have reliable resistance to fracture of the glass element under long-time or repeated static loading. 4. Dismantable joints with a hinge guarantee resistance to fracture under one-time loading to relatively high external pressures but do not perform well in an absolute sense and are therefore not recommended for introduction. 5. An efficient dismantable joint of glass elements was designed with ends in the area of the butt joint that have roughly the same stiffness, thus ensuring reliable resistance to fracture up to 1600 kgf/cm2 for spherical shells and up to 1400 kgf/cm2 for cylindrical shells and providing more than 100 cycles of service at 1000 kgf/cm2 for both. 6. A new dismantable joint combining a glass element with a high-stiffness metal flange was also developed. This joint withstands brief applications of pressure up to 1100 kgf/cm2 and ensures reliable shell operation under a cyclic load of 600 kgf/cm2 for 100 cycles. 7. The results of the findings from the above studies have been put to use by interested organizations to make new and more modern equipment.

Multirow joint fastener load investigation

A multirow joint subjected to the mechanical and thermal loadings was investigated to determine the loads taken by the fasteners in each row. The hole clearance was considered and its effect on the thermal expansion was defined. The friction in the interface between two plates in contact was analyzed and its effect on the distribution of fastener loads was determined. The primary joint design parameters, such as the material and size of the plates and of the fasteners and the patterns of fastener arrangement were considered. The principle of complementary virtual work was employed to derive the general equations involving these parameters, and the analytical solutions were obtained by solving the matrix equations. A computer program was developed to obtain the numerical solutions through the use of FORTRAN IV System 370/165 computer techniques. The application of the computer program to the practical joint design problems is discussed.