Research in this laboratory research is dedicated to the study of the mechanical behavior of materials and structures. Experimental and numerical techniques are utilized for the measurement and calculation of stresses, strains, and deformations. Current work emphasizes the mechanics and reliability of electronic packages. In one thrust, new piezoresistive sensors have been developed for silicon die surface stress measurement. These sensors ease calibration considerations and allow for more stress components to be measured. They have been incorporated into test chips and applied to particular electronic packages including quad flat packs, chip on board assemblies, ceramic pin grid arrays, ball grid arrays, and flip chip on laminate assemblies. In a second research thrust, the reliability of electronics in extreme environments (e.g. under-the-hood and aerospace) is being investigated. Both numerical and experimental methods are being used to evaluate thermally induced mechanical behavior. New procedures have been developed for evaluating the mechanical properties of solder and microelectronic encapsulants, and fatigue damage models are being used to predict solder failure. Numerical finite element predictions have been correlated with experimental stress and strain measurements made using piezoresistive stress sensors, holographic and moiré interferometry, and actual life testing. These investigations have been funded by the National Science Foundation, NASA, the Semiconductor Research Corporation (SRC), Sandia National Laboratories, and several industrial sponsors.
The Experimental and Computational Mechanics Laboratory occupies over 2000 ft 2 in the Department of Mechanical Engineering. It is complemented by a Mechanical Testing Laboratory, also within the Department of Mechanical Engineering, which houses several uniaxial and torsion testing machines for material characterization. The experimental portion of this solid mechanics research facility consists several smaller rooms devoted to interferometry techniques, microscopy and failure analysis, stress test chip measurements, and thermal imaging and heat transfer measurements. These rooms incorporate equipment for several methods of experimental stress analysis including conventional strain gages, advanced semiconductor sensors, computerized data acquisition, brittle coatings, photoelasticity and photoelastic coatings, holographic and speckle interferometry, shearing interferometry and coherent gradient sensing, moiré and moiré interferometry, and high-speed photography. Major pieces of equipment include high speed data acquisition systems; several precision GPIB instruments including semiconductor parameter analyzers, multimeters, current sources, and switch systems; a micromechanical tension-torsion testing machine for use with very small test specimens; argon ion and helium neon lasers (continuous and cavity dumped pulse operation); a thermoplastic holographic recording system; a moiré interferometry system; vibration isolation tables; digital image processing system; two computer controlled ovens with a range of -175 to 300 C; two environmental/humidity chambers; a PGC temperature/humidity control unit; an infrared thermal imaging system; several transmission and reflection polariscopes, and a wide variety of optical components and cameras. The numerical part of the laboratory consists of a computational room comprised of 5 Sun Ultrasparc Workstations, 10 Intel Pentium 4 based personal computers, 2 Terabytes of hard disk storage, archival tape drives, scanners, and laser and color printers.
The research in the lab deals with the development of optical/interferometric
sensors and failure mechanics of advanced materials. Over the years novel techniques
based on laser speckle and geometric moiré methods for mapping three-dimensional
deformations near cracks in ductile materials have been developed. Also, a novel
real-time optical method called Coherent Gradient Sensing (CGS), suitable for
dynamic fracture studies when used in conjunction with ultra-high speed photography,
has been developed. Dynamic fracture mechanics of polymers, high strength steels
and dissimilar material interfaces have been successfully studied using this new
tool. Recently, an infrared interferometric sensor has been developed to perform
rough surface metrology and flaw detection. The sensor is successfully used for
real-time fracture mechanics studies on plastically deformed ductile homogeneous
materials and bi-material (solder-copper) interfaces. Current interests include
development and failure characterization of emerging materials such as functionally
graded materials and porous/micro-cellular materials for thermal barrier coatings,
light-weight structures, and surface engineering. The research has been sponsored
by NSF, ARO, and AFOSR.
The equipment in this laboratory includes a high speed imaging facility (rotating mirror type and ultrahigh-speed digital cameras), a high-speed transient data acquisition system (multi-channel DAQ; 2.5 million samples/sec), several laser-based interferometers (visible light and infrared), a Spectra-Physics High power Argon-ion pulse-laser, an Instron universal testing machine, a high-velocity gas gun and Dynatup 9250-HV drop tower, a material preparation facility (processing of polymeric functionally graded materials, syntactic foams and nano-composites), and equipment for ultrasonic pulse-echo measurements.
The Fluid Mechanics Research Laboratory is a modern facility dedicated to both
fundamental and applied experimental studies of complex fluid flow problems. Along
these lines, state-of-the-art laser-based flow diagnostic tools, including a TSI
one-component laser Doppler velocimeter (LDV), LDV computer-controlled data acquisition
system, laser sheet visualization unit and digital image processing hardware &
software are routinely used in research studies to elucidate spatially-resolved
velocity field, turbulence data and qualitative flow pattern information. Computational
fluid dynamics (CFD) codes have been developed in-house and along with a number
of commercial codes, they are used to verify and complement the experimental studies.
At the present time, the experimental and computational studies under progress are concerned with transport phenomena in materials processing. For instance, we have constructed two transparent experimental test-sections to study the simulated flow of liquid steel in mold of continuous casters and liquid aluminum in a tundish. These projects have been supported by both internal and external supporters, such as ALCOA and Cray Research. In both projects we are interested in predicting and measuring the complex liquid metal flow fields and observe the effects of various geometrical and process conditions on the resulting flow fields.
In this laboratory, nonlinear and electro-optical properties of novel materials and microstructures are studied. Such materials have many potential applications in future electronics and photonics technologies. Specific organic molecular crystals and microstructures have unique characteristics that are suitable for ultrafast all-optical switching, logic operations and frequency conversion. The response time of such switching is expected to be three orders of magnitude faster than electronic switching that are commonly used. Therefore, these novel materials have currently attracted significant research attention.
The laboratory is equipped to perform a variety of optical techniques to measure nonlinear optical properties and dynamics of excited states over a very short period of time (less than 10 -12 sec). These methods include time resolved four wave mixing, excitation-probe, non-linear interferometry, waveguiding, frequency conversion, and z-scan. The laboratory is equipped with a high power laser with picosecond pulses and other required data acquisition systems for picosecond optics.
Dr. Malcolm Crocker
Dr. PK Raju
This Laboratory has current state-of-the-art equipment for measurement and analysis of sound and vibration signals. In particular, it has a Real Time Analyzer (B & K 2133). This is very useful for sound intensity, sound power, reverberation time and other measurements. Also this laboratory has two FFT Dual Channel Analyzers (B & K 2032 and Ono-Sokki CF950) for analysis and measurement of noise and vibration signals. Finite Element, FEM Boundary Element BEM and Statistical Energy Analysis SEA software packages, several sets of transducers, microphones, exciters are available in this laboratory.
The Sound and Vibration laboratory also has three small reverberation chambers and one anechoic chamber. Two of the reverberation chambers are in close proximity so that they can be used for transmission loss measurements of partitions. These two reverberation chambers are vibration-isolated from each other and the ground.
Some of the areas of research conducted in this laboratory are sound power measurement of machines using sound intensity technique, evaluation of transmission loss of structures, measurement of vibration damping of composite materials, non-destructive evaluation and characterization of composite materials using acoustic and vibration techniques, acoustic scattering and radiation from structures and active vibration control. Research in these areas have been funded by agencies including NASA, DOD, NSF and companies such as IBM and Trane and trade organizations such as American Gas Association.
