The research in the Mechanics of Materials Research Laboratory at URI focuses on experimental/analytical/numerical investigations of deformation and damage mechanisms in metallic alloys. In this, the role of material factors such as dislocation arrangements, twins evolution rate, slip band density, second phases, precipitates, grain size (coarse and ultra fine) and grain boundary morphology (planar and serrated) are tested and examined by simulating their interactions using computational and analytically based multi-physics models. Calibration of these models are supported by results obtained from experimental programs which include low cycle fatigue response (< 10-3 s-1), crack growth measurements (rate and crack tip closure characteristics), high strain rate and planar impact tests (> 104 s-1). These tests are conducted in air and vacuum environment at temperatures ranging from -196°C up to 1200°C. These tests are supported by a host of experimental laboratories including servohydraulic material testing systems, creep machines, Split Hopkinson Pressure Bar system, high pressure gas gun, optical and scanning electron microscopes and various equipment for specimen preparation.
The MMRL houses the following facilities:
- Mechanics of Materials Testing Systems
- Creep Testing Machines
- High Strain Rate Testing Equipment
- Ultrafine Grain Manufacturing Facilities
- Specimen Preparation and Heat Treatment Laboratory
- Optical and Scanning Electron Microscope
- Computational Facilities
MECHANICS OF MATERIALS TESTING LABORATORY
Four uniaxial servohydraulic MTS testing machines (with TestStar IIs control) equipped with high temperature and complex programming capabilities. Each machine has a 100 kN load cell, ±100 mm LVDT, strain channel, input/output channels data acquisition for temperature and/or voltage measurements. Testing experience includes low cycle fatigue testing, small and long crack growth testing, notch analysis, etc. The lab is supporting by a machine shop for making specimen grips and testing apparatus for different specimen types. Specimen types include smooth bar, compact tension (CT12.5, CT20 and CT40) and thin sheet geometry.
Low Cycle Fatigue Tests
MTS machine, with 2 zone ATS furnace, with room (knife-edge) or high temperature (quartz rod) water-cooled extensometer for strain controlled experiments. Programming for low cycle fatigue testing includes strain or load control, monotonic, stress relaxation, cyclic, with and without dwell times and variable strain rates for strain rate sensitivity testing and complex loading scenarios.
Crack Growth Tests (Air Environment)
Four MTS machine each equipped with 2-zone ATS furnace, potential drop system (Ectron 2 channel filter and amplifier), optical microscopes and Questar far field optical microscope for crack length measurements and crack opening displacement capabilities (high temperature scissor extension with clip gage). Programming capabilities for crack growth testing includes high and low frequency triangular or sinusoidal wave shape, dwell time loading (dwell at minimum or maximum load), creep crack growth testing (dwell at maximum load until complete failure), load shedding methods and complex loading scenarios.
Crack Growth Tests (Vacuum Environment)
MTS machine, with heating carried out using Encur 5kW induction heating unit with thermocouple feedback control, vacuum is achieved with Varian turbo pump (Turbo-V 300HT) capable of reaching 10-8 torr, potential drop system (Ectron 2 channel filter and amplifier) and Questar far field optical microscope for crack length measurements. Far field microscope is equipped with a camera and Image Control image acquisition system. Programming capabilities for crack growth testing includes high and low frequency triangular or sinusoidal wave shape, dwell time loading (dwell at minimum or maximum load), creep crack growth testing (dwell at maximum load until complete failure), load shedding methods and complex loading scenarios.
CREEP TESTING LABORATORY
ATS dual ratio lever arm testing machine with a 20,000 lbs (88.96 kN) capacity and data acquisition software. This can be used for classical creep testing and creep crack growth testing. High temperature capabilities include a 2 zone furnace and high temperature extensometer. Crack length is measured by a potential drop system and optical microscope.
HIGH STRAIN RATE TESTING LABORATORY
A- Compressive Split Hopkinson Pressure Bar (SHPB) Apparatus
The bar is capable of strain rates in the range of 102-104 s-1. The incident and transmitter bars are 50″ long and 0.75″ in diameter made of heat treated Maraging steel, with striker bar’s of lengths 2″, 4″, 8″ and 10″ long. The gas gun pressure chamber can reach 500 psi input and is equipped with a quick release solenoid valve, resulting velocities reaching 110 m/s. The SHPB is equipped with an automated timing relay for individual bar positioning using pneumatic bar actuator and firing gun. Strain in transmitted and incident bars is measured using Vishay 2300 Signal Conditioner Amplifier and Tektronic DPO 3034 Digital Oscilloscope. The bar is also equipped with tungsten carbide inserts for testing at temperatures ranging from -196°C up to 1000°C. Low temperature testing is carried out in a liquid nitrogen bath and high temperature testing is carried out using an Encur 5 kW induction heating unit with active temperature feedback control.
B- High Pressure Gas Gun
A single stage gun capable of strain rates > 105 s-1, equipped with high power infrared lasers and fast responding photodiodes for projectile velocity measurement. Stress measurements in the target specimen are measured using a piezoresistive manganin stress gauge, excited with a Dynasen pulse power supply for duration 600 micro-seconds. Stress and velocity measurements are acquired using Tektronic DPO 3034 Digital Oscilloscope. The gas gun pressure vessel is made of 17-4 PH stainless steel and has a 10,000 psi input pressure capacity. The barrel is 10 ft long with a 2” diameter bore, honed to 8Ra surface roughness carrying a 300 gram sabot carriage for plate impact projectile. A unique 2-stage pressure release system has been developed using two sets of rupture discs to achieve infinite increments of input pressure and instantaneous release. Entire system is placed under vacuum, down to 10-4 torr reducing drag effects, resulting in projectile velocities reaching greater than 1000 m/s.
ULTRAFINE GRAIN MANUFACTURING FACILITIES
100 ton Dake press equipped with a 90° equal channel angular press (ECAP) with a capacity of a 0.5 in and 1 in square billet size. This ECAP system applies severe plastic deformation to coarse grained materials (40-50 micron grain size) to produce ultrafine grained materials (< 5 micron grain size).
METAL MATRIX FIBER PUSH-OUT SYSTEM
Fiber push-out system to measure fiber/matrix interphase decohesion strength. The system operates at ultra high vacuum (<10-8 torr) and temperature levels > 800°C. The operation of the system utilizes a high resolution stepper motor coupled with linear motion feedthrough, a miniature load cell, and x-y positioning stage. The system has been developed in cooperation with NASA Lewis Research Center.
HEAT TREATMENT FACILITIES
Heat Treatment capabilities at temperatures up to 1500°C with computer controlled heating durations, cooling rates and data acquisition. The lab is equipped with:
- Thermolyne front loading furnace with programming capabilities
- Clam shell furnace
- MHI horizontal tube furnace with programming capabilities
- Encur 5 kW induction heating unit with thermocouple feedback control and quick release apparatus for fast quenching cooling rates
- Vacuum heat treatment unit
SPECIMEN PREPARATION LABORATORY
- Buehler Polishing wheels (up to a 1 micron finish)
- Buehler Vibratory polisher
- Electro polishing and etching capabilities
- Diamond cut off saw
- Fischione Twin Jet electropolisher for TEM foil preparation
- Carbon and gold surface coating system
- Buehler Hardness tester
- Spot Welder
OPTICAL AND SCANNING ELECTRON MICROSCOPE LABORATORY
Microscopy work spans from examining material’s microstructure (γ’ precipitation in Ni-based superalloys, α/β lamella in Titanium, pearlite volume fraction in low carbon steel, etc.), performing quantitative stereology (measuring grain size, precipitate or second phase size, distribution or volume fraction, lamella size and spacing, twin volume fraction, grain boundary morphology, grain boundary serration height and wavelength etc.), or examining specimens post testing including fracture surfaces, grain boundary sliding, slip band spacing, or deformation twinning, etc.
JOEL 840 scanning electron microscope (SEM) equipped with LaB6 filament and in-situ high temperature loading stage.
Nikon Measuring Optical Microscope equipped with Clemex camera for image capturing.
COMPUTATIONAL FACILITIES
Multiple high speed computers, with program experience including:
- Abaqus (finite element modeling with user subroutines)
- Matlab (data analysis, modeling)
- iSIGHT (parameter optimization program)
- SigmaScan (image analysis)
- SigmaPlot (graphing)
- Several in-house codes have been developed to address investigations related to non-linear kinematic hardening using internal state variable and crystal plasticity modeling
