Hamouda Ghonem | University of Rhode Island (original) (raw)

Papers by Hamouda Ghonem

A study has been carried out to examine effects of blast loading on the microstructure deformatio... more A study has been carried out to examine effects of blast loading on the microstructure deformation response of A572 Grade 50 low carbon structural steel. Symmetrical planar impact experiments have been carried out using a single stage gas gun to drive projectiles to velocities between 200 and 500 m/sec resulting in low to moderate shock loading of disc type steel specimens. Longitudinal stress histories of the impacted specimens were captured at the back face of the loaded specimens with the use of manganin gages. A constitutive model was employed to numerically simulate the particle velocity at the impact surface as well the pressure distribution across the specimens as a function of impact duration. An analytical approach utilizing a deformation model was used to link twin volume fraction to blast severity. Post-mortem analysis was carried out on the impacted specimens with the use of optical and scanning microscopy in order to correlate the severity of the impacts with development of twinning within the microstructure. A comparison between the analytically calculated and experimentally measured twin volume fraction was used to optimize the material and deformation models and establish a correlation between impact pressure and deformation response of the steel under examination.

Chemical Biology & Drug Design, 2013

The binding free energies on human tubulin of selected colchicine and thiocolchicine compounds we... more The binding free energies on human tubulin of selected colchicine and thiocolchicine compounds were determined. Two methods were used for the determination of binding free energies: one is based on theoretical prediction simulating the dissociation of the compound from tubulin using a series of molecular dynamics simulations, and the other method involves a series of experiments that measured the affinity of the compound on a synthetically expressed and purified tubulin protein using a spectrofluorometric technique.

Composites Engineering, 1995

J Mater Eng Perform, 1995

Aging of silicon-bearing, near-alpha titanium alloys produces two types of precipitate, Ti3Al and... more Aging of silicon-bearing, near-alpha titanium alloys produces two types of precipitate, Ti3Al and (TiZr6Si3 (silicide). A postaging heat treatment that relies on the phenomenon of the critical ordering temperature is used to remove the Ti3Al precipitate while leaving the silicide intact. Three materials—unaged (precipitate free), overaged (Ti3Al plus silicide), and post aging heat treated (silicide only)— are compared. The objective is to identify the separate effects of the Ti3Al and silicide precipitates on tensile and fatigue crack growth behavior at room temperature and 593 °C. The Ti3Al precipitate is largely responsible for the increase in yield stress and for the decrease in ductility at both test temperatures. In contrast, the increase in room temperature fatigue crack growth rate associated with aging is attributed to the silicide, with Ti3Al playing only a minor role. Aging produces a slight improvement in fatigue crack resistance at 593 °C, which also appears to be due to the presence of the silicide precipitate.

Ecf10 Berlin 1994, Feb 6, 2013

Materials Science Engineering a Structural Materials Properties Microstructure and Processing, Jan 8, 2003

This paper deals with crack tip/microstructure interactions at 520 8C in lamellar Ti Á/6Al Á/2Sn ... more This paper deals with crack tip/microstructure interactions at 520 8C in lamellar Ti Á/6Al Á/2Sn Á/4Zr Á/2Mo Á/0.1Si (Ti6242) alloy under different fatigue loading frequencies. A series of heat treatments were performed in order to produce large colony microstructures that vary in their lamellar and colony size. Fatigue crack growth (FCG) experiments were conducted on these microstructures at loading frequencies of 10 and 0.05 Hz. The lower frequency was explored with and without imposing a 5 min hold-time at the peak stress level during each loading cycle. Results show that the crack growth behavior is sensitive to the loading frequency. For the same microstructure, the crack growth rate is found to be lower at 10 than at 0.05 Hz. The addition of a holdtime, however, did not alter the FCG rate indicating that creep strain during one loading cycle does not contribute significantly in the crack growth process. It is also shown that variations in lamella and colony size have no effects on the FCG rate except for the early stage of crack propagation. Scanning Electron Microscope examinations are performed on the fracture surface in order to identify the relevant crack growth mechanisms with respect to the loading frequency and the microstructure details. Quasi-cleavage of the a/b colonies along strong planar shear bands is shown to be a major mode of failure under all test condition. At a loading frequency of 10 Hz, the crack path proceeds arbitrary along planes either perpendicular or parallel to the long axis of a lamellae, while at 0.05 Hz, parallel-to-lamellae crack paths become favored. Corresponding differences of crack growth behavior are examined in terms of slip emission at the crack tip and interactions with the microstructure details. #

Metallurgical and Materials Transactions A

Metallurgical and Materials Transactions A

oMS No. 07O41ag and , t. drta regardin thi bre esitiat or " CtleIrn ean, at this ,oieon at inform... more oMS No. 07O41ag and , t. drta regardin thi bre esitiat or " CtleIrn ean, at this ,oieon at informationl. noiuding suqqiontif for reducing this burdenl. to Wailiinigtot O tada'fdurTo SipVtcas. O rectoratefr Informaion Ovierazio and pecom 12 Is Jefofmnw avos 44igmw. Suite 1204. Arlington, VA 22202-A302. a" to the Off iCa of Management aria SUdqet. 1`4OMWOfit fteduci.ton Project (07OA01g) Wo)*evji~on. OC 2goj.

GROWTH RATE, GRAIN BOUNDARY DUCTILITY, OXIDATION DIFFUSIVITY, INTERGRANULAR, HOLD TIME, SLIP, HOM... more GROWTH RATE, GRAIN BOUNDARY DUCTILITY, OXIDATION DIFFUSIVITY, INTERGRANULAR, HOLD TIME, SLIP, HOMOGENEITY 19. ABSTRACT (Continue on r everse if' r'ecsary And identify by blocx numnb~,)

High temperature fatigue crack growth experiments were carried out on Ti6242 alloy with large col... more High temperature fatigue crack growth experiments were carried out on Ti6242 alloy with large colony size in both air and vacuum environment. The alloy was heat treated to provide two different lamella size; fine and coarse. Tests were conducted at two temperatures, 520 o C and 590 o C, using two loading frequencies; 10 Hz and 0.05 Hz in air and 0.05 Hz in vacuum. All tests were performed at a stress ratio of 0.1. This study shows that at 520 o C/air, the fatigue crack growth rate is not significantly influenced by changes in the lamella size microstructure. For 0.05 Hz / low ∆K, however, the fatigue crack growth rate is higher in the fine lamellar microstructure and is accompanied with the appearance of a plateau. In air environment, the fatigue process is predominantly controlled by one single mechanism associated with transcolony fracture and formation of quasi-cleavage facets. In Vacuum conditions, the crack growth rate is not greatly influenced by temperature or lamella size. In comparing the fatigue crack growth rate in air and vacuum, the vacuum results are generally lower than the corresponding ones in air within the ∆K= 18-25 MPa√m. Above this level, the CGR data in both air and vacuum coincides thus indicating the role of environment in the low ∆K growth stage. A general hypothesis explaining the crack growth mechanisms in both air and vacuum is made in this study on the basis of scanning electron microscopic observations of the crack growth path in relation to the lamella direction as a function of loading frequency, temperature, lamella size and test environment.

A study has been carried out to examine effects of blast loading on the microstructure deformatio... more A study has been carried out to examine effects of blast loading on the microstructure deformation response of A572 Grade 50 low carbon structural steel. Symmetrical planar impact experiments have been carried out using a single stage gas gun to drive projectiles to velocities between 200 and 500 m/sec resulting in low to moderate shock loading of disc type steel specimens. Longitudinal stress histories of the impacted specimens were captured at the back face of the loaded specimens with the use of manganin gages. A constitutive model was employed to numerically simulate the particle velocity at the impact surface as well the pressure distribution across the specimens as a function of impact duration. An analytical approach utilizing a deformation model was used to link twin volume fraction to blast severity. Post-mortem analysis was carried out on the impacted specimens with the use of optical and scanning microscopy in order to correlate the severity of the impacts with development of twinning within the microstructure. A comparison between the analytically calculated and experimentally measured twin volume fraction was used to optimize the material and deformation models and establish a correlation between impact pressure and deformation response of the steel under examination.

Chemical Biology & Drug Design, 2013

The binding free energies on human tubulin of selected colchicine and thiocolchicine compounds we... more The binding free energies on human tubulin of selected colchicine and thiocolchicine compounds were determined. Two methods were used for the determination of binding free energies: one is based on theoretical prediction simulating the dissociation of the compound from tubulin using a series of molecular dynamics simulations, and the other method involves a series of experiments that measured the affinity of the compound on a synthetically expressed and purified tubulin protein using a spectrofluorometric technique.

Composites Engineering, 1995

J Mater Eng Perform, 1995

Aging of silicon-bearing, near-alpha titanium alloys produces two types of precipitate, Ti3Al and... more Aging of silicon-bearing, near-alpha titanium alloys produces two types of precipitate, Ti3Al and (TiZr6Si3 (silicide). A postaging heat treatment that relies on the phenomenon of the critical ordering temperature is used to remove the Ti3Al precipitate while leaving the silicide intact. Three materials—unaged (precipitate free), overaged (Ti3Al plus silicide), and post aging heat treated (silicide only)— are compared. The objective is to identify the separate effects of the Ti3Al and silicide precipitates on tensile and fatigue crack growth behavior at room temperature and 593 °C. The Ti3Al precipitate is largely responsible for the increase in yield stress and for the decrease in ductility at both test temperatures. In contrast, the increase in room temperature fatigue crack growth rate associated with aging is attributed to the silicide, with Ti3Al playing only a minor role. Aging produces a slight improvement in fatigue crack resistance at 593 °C, which also appears to be due to the presence of the silicide precipitate.

Ecf10 Berlin 1994, Feb 6, 2013

Materials Science Engineering a Structural Materials Properties Microstructure and Processing, Jan 8, 2003

This paper deals with crack tip/microstructure interactions at 520 8C in lamellar Ti Á/6Al Á/2Sn ... more This paper deals with crack tip/microstructure interactions at 520 8C in lamellar Ti Á/6Al Á/2Sn Á/4Zr Á/2Mo Á/0.1Si (Ti6242) alloy under different fatigue loading frequencies. A series of heat treatments were performed in order to produce large colony microstructures that vary in their lamellar and colony size. Fatigue crack growth (FCG) experiments were conducted on these microstructures at loading frequencies of 10 and 0.05 Hz. The lower frequency was explored with and without imposing a 5 min hold-time at the peak stress level during each loading cycle. Results show that the crack growth behavior is sensitive to the loading frequency. For the same microstructure, the crack growth rate is found to be lower at 10 than at 0.05 Hz. The addition of a holdtime, however, did not alter the FCG rate indicating that creep strain during one loading cycle does not contribute significantly in the crack growth process. It is also shown that variations in lamella and colony size have no effects on the FCG rate except for the early stage of crack propagation. Scanning Electron Microscope examinations are performed on the fracture surface in order to identify the relevant crack growth mechanisms with respect to the loading frequency and the microstructure details. Quasi-cleavage of the a/b colonies along strong planar shear bands is shown to be a major mode of failure under all test condition. At a loading frequency of 10 Hz, the crack path proceeds arbitrary along planes either perpendicular or parallel to the long axis of a lamellae, while at 0.05 Hz, parallel-to-lamellae crack paths become favored. Corresponding differences of crack growth behavior are examined in terms of slip emission at the crack tip and interactions with the microstructure details. #

Metallurgical and Materials Transactions A

Metallurgical and Materials Transactions A

oMS No. 07O41ag and , t. drta regardin thi bre esitiat or " CtleIrn ean, at this ,oieon at inform... more oMS No. 07O41ag and , t. drta regardin thi bre esitiat or " CtleIrn ean, at this ,oieon at informationl. noiuding suqqiontif for reducing this burdenl. to Wailiinigtot O tada'fdurTo SipVtcas. O rectoratefr Informaion Ovierazio and pecom 12 Is Jefofmnw avos 44igmw. Suite 1204. Arlington, VA 22202-A302. a" to the Off iCa of Management aria SUdqet. 1`4OMWOfit fteduci.ton Project (07OA01g) Wo)*evji~on. OC 2goj.

GROWTH RATE, GRAIN BOUNDARY DUCTILITY, OXIDATION DIFFUSIVITY, INTERGRANULAR, HOLD TIME, SLIP, HOM... more GROWTH RATE, GRAIN BOUNDARY DUCTILITY, OXIDATION DIFFUSIVITY, INTERGRANULAR, HOLD TIME, SLIP, HOMOGENEITY 19. ABSTRACT (Continue on r everse if' r'ecsary And identify by blocx numnb~,)

High temperature fatigue crack growth experiments were carried out on Ti6242 alloy with large col... more High temperature fatigue crack growth experiments were carried out on Ti6242 alloy with large colony size in both air and vacuum environment. The alloy was heat treated to provide two different lamella size; fine and coarse. Tests were conducted at two temperatures, 520 o C and 590 o C, using two loading frequencies; 10 Hz and 0.05 Hz in air and 0.05 Hz in vacuum. All tests were performed at a stress ratio of 0.1. This study shows that at 520 o C/air, the fatigue crack growth rate is not significantly influenced by changes in the lamella size microstructure. For 0.05 Hz / low ∆K, however, the fatigue crack growth rate is higher in the fine lamellar microstructure and is accompanied with the appearance of a plateau. In air environment, the fatigue process is predominantly controlled by one single mechanism associated with transcolony fracture and formation of quasi-cleavage facets. In Vacuum conditions, the crack growth rate is not greatly influenced by temperature or lamella size. In comparing the fatigue crack growth rate in air and vacuum, the vacuum results are generally lower than the corresponding ones in air within the ∆K= 18-25 MPa√m. Above this level, the CGR data in both air and vacuum coincides thus indicating the role of environment in the low ∆K growth stage. A general hypothesis explaining the crack growth mechanisms in both air and vacuum is made in this study on the basis of scanning electron microscopic observations of the crack growth path in relation to the lamella direction as a function of loading frequency, temperature, lamella size and test environment.