A detailed three-dimensional finite element model of a bridge joint with link slab continuity was... more A detailed three-dimensional finite element model of a bridge joint with link slab continuity was developed and subjected to the same loading conditions as a three-dimensional finite element model of a bridge joint with a continuity diaphragm. Support conditions and material properties were homogenized between both models, and in order to determine the equivalent loading resulting from temperature gradient, a validated simplified line model was used. Displacements and rotations were then determined for the conditions in the detailed 3D model using the simplified line model and were applied to the corresponding elements in the 3D model. Results showed a different stress distribution between both models. The higher continuity of the continuity diaphragm joint led to better stress distribution in the deck than the link slab joint in the partial continuity model. Bearing pads had different roles in both models and therefore different stress distribution and displacement field. The higher redundancy of the continuity diaphragm resulted in less influence of the bearing pads towards joint performance in the continuity diaphragm model than in the link slab model.
Post-weld heat treatment (PWHT) is commonly adopted on welded joints and structures to relieve po... more Post-weld heat treatment (PWHT) is commonly adopted on welded joints and structures to relieve post-weld residual stresses; and restore the mechanical properties and structural integrity. An electrolytic plasma process (EPP) has been developed to improve corrosion behavior and wear resistance of structural materials; and can be employed in other applications and surface modifications aspects. In this study the effects of PWHT and EPP on the residual stresses, micro-hardness, microstructures, and uniaxial tensile properties are explored on tungsten inert gas (TIG) welded AISI-4140 alloys steel with SAE-4130 chromium-molybdenum alloy welding filler rod. For rational comparison all of the welded samples are checked with nondestructive Phased Array Ultrasonic Testing (PAUT) and to ensure defect-free samples before testing. Residual stresses are assessed with ultrasonic testing at different distances from weld center line. PWHT resulted in relief of tensile residual stress due to grain refinement. As a consequence higher ductility but lower strength existed in PWHT samples. In comparison, EPP-treated samples revealed lower residual stresses, but no significant variation on the grain refinement. Consequently, EPP-treated specimens exhibited higher tensile strength but lower ductility and toughness for the martensitic formation due to the rapid heating and quenching effects. EPP was also applied on PWHT samples, but which did not reveal any substantial effect on the tensile properties after PWHT at 650°C. Finally the microstructures and fracture morphology are analyzed using scanning electron microscopy (SEM) and optical microscope to study the evolution of microstructures.
Fusion welding of Aluminum and its alloys is a great challenge for the structural integrity of li... more Fusion welding of Aluminum and its alloys is a great challenge for the structural integrity of lightweight material structures. One of the major shortcomings of Aluminum alloy welding is the inherent existence of defects in the welded area. In the current study, tests have been conducted on tungsten inert gas (TIG) welded AA6061-T651 aluminum alloy to determine the effects of defect sizes and its distribution on fracture strength. The information will be used to establish weld acceptance/rejection criteria. After welding, all specimens were non-destructively inspected with phased array ultrasonic and measured the projected area of the defects. Tensile testing was performed on inspected specimens containing different weld defects: such as, porosity, lack of fusion, and incomplete penetration. Tensile tested samples were cut along the cross section and inspected with Optical Microscope (OM) to measure actual defect sizes. Tensile properties were correlated with phased array ultrasonic testing (PAUT) results and through microscopic evaluations. Generally, good agreement was found between PAUT and microscopic defect sizing. The tensile strength and toughness decreased with the increase of defect sizes. Small voids (area ratio <0.04) does not have significant effect on the reduction of tensile strength and toughness values. Once defective “area ratio (cross sectional area of the defect) / (total specimen cross sectional area)” reached a certain critical value (say, 0.05), both strength and toughness values decline sharply. After that critical value both the tensile strength and toughness values decreases linearly with the increase of defect area ratio.
ABSTRACT Heat-treatable AA-6061-T651 Aluminum alloys (Al-Mg-Si) have found considerable importanc... more ABSTRACT Heat-treatable AA-6061-T651 Aluminum alloys (Al-Mg-Si) have found considerable importance in structural and aerospace applications for their high strength to weight ratio and improved corrosion resistance properties. Intrinsic weld defects, post-weld residual stresses, and microstructural changes are the key factors for performance reductions and failures of welded structures. Gas-Tungsten-Arc-Welding (TIG/GTAW) was carried out on AA-6061-T651 plates with Argon/Helium (50/50) as the shielding gases. Non-destructive Phased-Array-Ultrasonic- Testing (PAUT) was applied for the detection and characterization of weld defects and mechanical performances. Ultrasonic technique was used for the evaluation of post-weld residual stresses in welded components. The approach is based on the acoustoelastic effect, in which ultrasonic wave propagation speed corresponds to the magnitude of stresses present within the materials. To verify the PAUT’s residual stress results, a semi-destructive hole-drilling technique was used; and observed analogous results. The effects of post-weld-heat-treatment (PWHT) on the residual stresses, grain size, micro-hardness, and tensile properties are also studied. The grain size and micro-hardness values are studied through Heyn’s method and Vickers hardness test, respectively. Lower residual stresses are observed in post-weld heat-treated specimens, which are also confirmed from microstructural and micro-hardness studies. The PWHT enhanced tensile properties for the redistribution of microstructures and residual stresses.
Strengthening-By-Stiffening (SBS) is a new concept developed to enhance the strength and performa... more Strengthening-By-Stiffening (SBS) is a new concept developed to enhance the strength and performance of shear-deficient thin-walled steel girders. In SBS, pultruded composite sections are bonded to buckling prone web panels to serve as stiffeners.
Heat treatable AA-6061 T651 Aluminum alloys (Al-Mg-Si) have found considerable importance in vari... more Heat treatable AA-6061 T651 Aluminum alloys (Al-Mg-Si) have found considerable importance in various structural applications for their high strength to weight ratio and corrosion resistance properties. Weld defects, residual stresses, and microstructural changes are the key factors for the performance reduction as well as failure of welded structures. Tungsten inert gas (TIG/GTAW) welding was carried out on AA-6061 T651 Aluminum Alloy plates using Argon/Helium (50/50) as the shielding gas. Non-destructive phased array ultrasonic testing (PAUT) was applied for the detection and characterization of weld defects and characterization of the mechanical performances. In this study, ultrasonic technique was also used for the evaluation of post-weld residual stresses in welded components. The approach is based on the acoustoelastic effect, in which ultrasonic wave propagation speed is related to the magnitude of stresses present in the materials. To verify the estimated residual stresses by ultrasonic testing, hole-drilling technique was carried out and observed analogous results. The effects of post weld heat treatment (PWHT) on the residual stresses, grain size, micro hardness, and tensile properties were also studied. The grain size and micro hardness were studied through Heyn’s method and Vickers hardness test, respectively. Lower residual stresses were observed in post-weld heat-treated specimens, which also experienced from microstructure and micro hardness studies. The PWHT also resulted enhanced tensile properties for the redistribution of microstructures and residual stresses.
Reliability analysis of Cone Penetration Test (CPT) is very useful information for interpreting C... more Reliability analysis of Cone Penetration Test (CPT) is very useful information for interpreting CPT data. One of the identified sources of uncertainty is the inherent variation in the measurement device and equipment. This uncertainty needs to be accounted for in the reliability analysis forming the basis for the correlation of the CPT with soils engineering properties. This paper investigates the variability of CPT measurements by conducting sixteen CPT penetrations in proximity to each other to a depth of 24.4 m (80 ft). A reliability analysis is conducted to determine the coefficient of variation (COV) of q c as well as soil unit weight (γT ) and overburden pressure (σ vo). The results showed that COV qc () is higher when compared to COV (γT ) and COV(σ vo), with values close to 40% in some cases. On average, the COV for qc , γT and σ vo are 19.6%, 1.46%, and 0.51%, respectively. ABSTRACT: Reliability analysis of Cone Penetration Test (CPT) is very useful information for interpreting CPT data. One of the identified sources of uncertainty is the inherent variation in the measurement device and equipment. This uncertainty needs to be accounted for in the reliability analysis forming the basis for the correlation of the CPT with soils engineering properties. This paper investigates the variability of CPT measurements by conducting sixteen CPT penetrations in proximity to each other to a depth of 24.4 m (80 ft). A reliability analysis is conducted to determine the coefficient of variation (COV) of q c as well as soil unit weight (γT ) and overburden pressure (σ vo). The results showed that COV qc
This paper reports on a survey effort of damaged bridges conducted by the writers in the aftermat... more This paper reports on a survey effort of damaged bridges conducted by the writers in the aftermath of Hurricane Katrina of August 2005. As with Hurricane Ivan in 2004, low-lying coastal bridges suffered severe damage due to hydrodynamic forces caused by storm surge. Consequently, transportation networks in the affected areas were disrupted. Since coastal bridges are considered lifelines for the communities they serve, their loss resulted in hindering rescue and recovery efforts. The purpose of this paper is to present related data as observed by the writers. Data collection and documentation of perishable data after natural disasters and before recovery and reconstruction efforts is of great importance. In the case of coastal bridges, they can help in improving future designs and rehabilitating existing ones. The majority of the surveyed bridges collapsed due to unseating. Hydrodynamic forces due to wave impact and water current on the superstructure proved to exceed the capacity of common connections between the superstructure and the substructure for short- and medium-span bridges.
Advances in Materials and Processing Technologies, Feb 10, 2019
Friction stir welding (FSW) as a solid state joining process is being known recently by many indu... more Friction stir welding (FSW) as a solid state joining process is being known recently by many industries due to its capability to reduce defects, energy efficient, and environment friendly compared with conventional techniques. Specifically, FSW can be used to join highstrength aluminum alloys like 7XXX and 2XXX which are hard to weld by conventional fusion welding. In this review paper, the elementary principles of FSW, parameters, and the effect of the FSW parameters on microstructure and mechanical properties are addressed. Although this process has a lot of advantages compared with fusion techniques, however, many problems still remain unsolved related to poor mechanical properties of weldment's heat affected zone (HAZ). In this regard, the impact of post weld heat treatment (PWHT) on improvement of joint properties is addressed. Finally, appropriate parameters and factors for achieving the best condition of the weld is discussed.
Journal of Composites for Construction, Aug 1, 2017
AbstractRestoring the capacity of deficient structural members to meet original design requiremen... more AbstractRestoring the capacity of deficient structural members to meet original design requirements or new higher demands is common. For that purpose, research efforts to use composite materials in...
Journal of Manufacturing Science and Engineering-transactions of The Asme, Sep 4, 2015
Welding defects and the reduction of mechanical performances are the foremost problems for fusion... more Welding defects and the reduction of mechanical performances are the foremost problems for fusion welded aluminum alloys joints. The influences of weld defects and postweld heat treatment (PWHT) on tensile properties of gas tungsten arc (GTA) welded aluminum alloy AA-6061-T651 joints are investigated in this current study. All welded specimens are nondestructively inspected with phased array ultrasonic testing (PAUT) to classify weld defect and measure the projected defects area-ratio (AR). Ultimate tensile strength (UTS) decreased linearly with the increase of the size of weld defect but tensile toughness behaved nonlinearly with defect size. Depending on defect size, defective samples' joint efficiency (JE) varied from 35% to 48% of base metal's (BM) UTS. Defect-free as-welded (AW) specimens observed to have 53% and 34% JE based on UTS and yield strength (YS) of BM, respectively. PWHT was applied on defect-free welded specimens to improve tensile properties by precipitation hardening, microstructures refining, and removal of postweld residual stresses. Solution treatment (ST) (at 540 °C) followed by varying levels of artificial age-hardening (AH) time was investigated to obtain optimum tensile properties. For GTA-welded AA-6061-T651, peak aging time was 5 hr at 180 °C. PWHT specimens showed 85% JE based on UTS and up to a 71% JE based on YS of BM. However, toughness values decreased about 29% due to the presence of precipitate-free fusion zones. The experimental investigations can be used to establish weld acceptance/rejection criteria and for the design of welded aluminum alloy structures.
The International Journal of Advanced Manufacturing Technology, Nov 17, 2017
Building a reliable prediction model can mitigate the need for actual experiments, hence saving t... more Building a reliable prediction model can mitigate the need for actual experiments, hence saving time and cost. To this end, this study presents a methodology to predict weld quality for a particular friction stir weld configuration using machine learning and metaheuristic algorithms including K-nearest neighbor (KNN), fuzzy KNN (FKNN), and the artificial bee colony (ABC). The ABC algorithm was utilized to determine the best (F)KNN model with optimal K value and feature subset. First, models were built based on only experimental conditions including spindle rotational speed, plunge force, and feed rate, as well as derived values including a speed ratio and an empirical force index (EFI). The best model was identified to be 1-NN comprised of three features, i.e., rotational speed, feed rate, and EFI, with 93.16% classification accuracy based on leave-one-out cross-validation. The majority of data points leading to error were found to lie mostly on the boundaries between classes. It was shown that classification error could be reduced by removing those points, which is cheating and not recommended. Instead, it is recommended to improve classification accuracy without omitting dissenting data by introducing additional information to better distinguish misclassified data points. To this end, wavelet energy features extracted from weld signals of X-Force, Y-Force, spindle rotational speed, feed rate, and plunge force were added to the original feature pool. In order to determine the impact of each weld signal feature set, each signal feature set was individually tested. After applying ABC to the expanded feature pool to build the best model, perfect classification accuracy was achieved in several cases. The results suggest that adding signal features can greatly improve the effectiveness of model predictability of friction stir weld quality.
Acta Metallurgica Sinica (english Letters), Oct 4, 2017
This paper presents a new thermomechanical model of friction stir welding which is capable of sim... more This paper presents a new thermomechanical model of friction stir welding which is capable of simulating the three major steps of friction stir welding (FSW) process, i.e., plunge, dwell, and travel stages. A rate-dependent Johnson-Cook constitutive model is chosen to capture elasto-plastic work deformations during FSW. Two different weld schedules (i.e., plunge rate, rotational speed, and weld speed) are validated by comparing simulated temperature profiles with experimental results. Based on this model, the influences of various welding parameters on temperatures and energy generation during the welding process are investigated. Numerical results show that maximum temperature in FSW process increases with the decrease in plunge rate, and the frictional energy increases almost linearly with respect to time for different rotational speeds. Furthermore, low rotational speeds cause inadequate temperature distribution due to low frictional and plastic dissipation energy which eventually results in weld defects. When both the weld speed and rotational speed are increased, the contribution of plastic dissipation energy increases significantly and improved weld quality can be expected.
Friction stir welding (FSW) is a solid-state joining process, where joint properties largely depe... more Friction stir welding (FSW) is a solid-state joining process, where joint properties largely depend on the amount of heat generation during the welding process. The objective of this paper was to develop a numerical thermomechanical model for FSW of aluminum-copper alloy AA2219 and analyze heat generation during the welding process. The thermomechanical model has been developed utilizing ANSYS Ò APDL. The model was verified by comparing simulated temperature profile of three different weld schedules (i.e., different combinations of weld parameters in real weld situations) from simulation with experimental results. Furthermore, the verified model was used to analyze the effect of different weld parameters on heat generation. Among all the weld parameters, the effect of rotational speed on heat generation is the highest.
Journal of Composites for Construction, Nov 1, 2001
Extensive testing has shown that externally bonded carbon fiber reinforced polymer (CFRP) laminat... more Extensive testing has shown that externally bonded carbon fiber reinforced polymer (CFRP) laminates are particularly suited for improving the short-term behavior of deficient reinforced concrete beams. Accelerated fatigue tests conducted to date confirm that fatigue response is also improved. This paper describes an analytical model for simulating the static response and accelerated fatigue behavior of reinforced concrete beams strengthened with CFRP laminates. Static and fatigue calculations are carried out using a fiber section model that accounts for the nonlinear time-dependent behavior of concrete, steel yielding, and rupture of CFRP laminates. Analysis results are compared with experimental data from two sets of accelerated fatigue tests on CFRP strengthened beams and show good agreement. Cyclic fatigue causes a time-dependent redistribution of stresses, which leads to a mild increase in steel and CFRP laminate stresses as fatigue life is exhausted. Based on the findings, design considerations are suggested for the repair and/or strengthening of reinforced concrete beams using CFRP laminates.
Journal of Materials in Civil Engineering, Oct 1, 2015
Nondestructive testing (NDT) methods for identifying stress levels in materials mostly rely on th... more Nondestructive testing (NDT) methods for identifying stress levels in materials mostly rely on the theory of acoustoelasticity. However, the sensitivity and the accuracy of acoustoelasticity are affected by several factors such as the (1) type, (2) propagation, and (3) polarization directions of the used signals. This paper presents the results of an experimental investigation of longitudinal waves propagating perpendicular to the applied uniaxial tensile stresses in structural steel specimens. The changes in four ultrasonic signal characteristics were investigated with increasing stress levels ranging from below to above the yield stress of steel. The considered signal characteristics were the peak amplitudes and signal energy in the time domain, and the fast Fourier transform (FFT) and chirp-Z transform (CZT) in the frequency domain. Even though the acoustoelastic effect on the type ultrasonic signal used is very small, clear distinctions between prior to and postyielding are observed for all investigated parameters. The results are presented with a detailed statistical and receiver operating characteristics (ROCs) analyses. The results show that identifying damage to steel structures due to local yielding is possible using the simple ultrasonic signal classification.
A detailed three-dimensional finite element model of a bridge joint with link slab continuity was... more A detailed three-dimensional finite element model of a bridge joint with link slab continuity was developed and subjected to the same loading conditions as a three-dimensional finite element model of a bridge joint with a continuity diaphragm. Support conditions and material properties were homogenized between both models, and in order to determine the equivalent loading resulting from temperature gradient, a validated simplified line model was used. Displacements and rotations were then determined for the conditions in the detailed 3D model using the simplified line model and were applied to the corresponding elements in the 3D model. Results showed a different stress distribution between both models. The higher continuity of the continuity diaphragm joint led to better stress distribution in the deck than the link slab joint in the partial continuity model. Bearing pads had different roles in both models and therefore different stress distribution and displacement field. The higher redundancy of the continuity diaphragm resulted in less influence of the bearing pads towards joint performance in the continuity diaphragm model than in the link slab model.
Post-weld heat treatment (PWHT) is commonly adopted on welded joints and structures to relieve po... more Post-weld heat treatment (PWHT) is commonly adopted on welded joints and structures to relieve post-weld residual stresses; and restore the mechanical properties and structural integrity. An electrolytic plasma process (EPP) has been developed to improve corrosion behavior and wear resistance of structural materials; and can be employed in other applications and surface modifications aspects. In this study the effects of PWHT and EPP on the residual stresses, micro-hardness, microstructures, and uniaxial tensile properties are explored on tungsten inert gas (TIG) welded AISI-4140 alloys steel with SAE-4130 chromium-molybdenum alloy welding filler rod. For rational comparison all of the welded samples are checked with nondestructive Phased Array Ultrasonic Testing (PAUT) and to ensure defect-free samples before testing. Residual stresses are assessed with ultrasonic testing at different distances from weld center line. PWHT resulted in relief of tensile residual stress due to grain refinement. As a consequence higher ductility but lower strength existed in PWHT samples. In comparison, EPP-treated samples revealed lower residual stresses, but no significant variation on the grain refinement. Consequently, EPP-treated specimens exhibited higher tensile strength but lower ductility and toughness for the martensitic formation due to the rapid heating and quenching effects. EPP was also applied on PWHT samples, but which did not reveal any substantial effect on the tensile properties after PWHT at 650°C. Finally the microstructures and fracture morphology are analyzed using scanning electron microscopy (SEM) and optical microscope to study the evolution of microstructures.
Fusion welding of Aluminum and its alloys is a great challenge for the structural integrity of li... more Fusion welding of Aluminum and its alloys is a great challenge for the structural integrity of lightweight material structures. One of the major shortcomings of Aluminum alloy welding is the inherent existence of defects in the welded area. In the current study, tests have been conducted on tungsten inert gas (TIG) welded AA6061-T651 aluminum alloy to determine the effects of defect sizes and its distribution on fracture strength. The information will be used to establish weld acceptance/rejection criteria. After welding, all specimens were non-destructively inspected with phased array ultrasonic and measured the projected area of the defects. Tensile testing was performed on inspected specimens containing different weld defects: such as, porosity, lack of fusion, and incomplete penetration. Tensile tested samples were cut along the cross section and inspected with Optical Microscope (OM) to measure actual defect sizes. Tensile properties were correlated with phased array ultrasonic testing (PAUT) results and through microscopic evaluations. Generally, good agreement was found between PAUT and microscopic defect sizing. The tensile strength and toughness decreased with the increase of defect sizes. Small voids (area ratio <0.04) does not have significant effect on the reduction of tensile strength and toughness values. Once defective “area ratio (cross sectional area of the defect) / (total specimen cross sectional area)” reached a certain critical value (say, 0.05), both strength and toughness values decline sharply. After that critical value both the tensile strength and toughness values decreases linearly with the increase of defect area ratio.
ABSTRACT Heat-treatable AA-6061-T651 Aluminum alloys (Al-Mg-Si) have found considerable importanc... more ABSTRACT Heat-treatable AA-6061-T651 Aluminum alloys (Al-Mg-Si) have found considerable importance in structural and aerospace applications for their high strength to weight ratio and improved corrosion resistance properties. Intrinsic weld defects, post-weld residual stresses, and microstructural changes are the key factors for performance reductions and failures of welded structures. Gas-Tungsten-Arc-Welding (TIG/GTAW) was carried out on AA-6061-T651 plates with Argon/Helium (50/50) as the shielding gases. Non-destructive Phased-Array-Ultrasonic- Testing (PAUT) was applied for the detection and characterization of weld defects and mechanical performances. Ultrasonic technique was used for the evaluation of post-weld residual stresses in welded components. The approach is based on the acoustoelastic effect, in which ultrasonic wave propagation speed corresponds to the magnitude of stresses present within the materials. To verify the PAUT’s residual stress results, a semi-destructive hole-drilling technique was used; and observed analogous results. The effects of post-weld-heat-treatment (PWHT) on the residual stresses, grain size, micro-hardness, and tensile properties are also studied. The grain size and micro-hardness values are studied through Heyn’s method and Vickers hardness test, respectively. Lower residual stresses are observed in post-weld heat-treated specimens, which are also confirmed from microstructural and micro-hardness studies. The PWHT enhanced tensile properties for the redistribution of microstructures and residual stresses.
Strengthening-By-Stiffening (SBS) is a new concept developed to enhance the strength and performa... more Strengthening-By-Stiffening (SBS) is a new concept developed to enhance the strength and performance of shear-deficient thin-walled steel girders. In SBS, pultruded composite sections are bonded to buckling prone web panels to serve as stiffeners.
Heat treatable AA-6061 T651 Aluminum alloys (Al-Mg-Si) have found considerable importance in vari... more Heat treatable AA-6061 T651 Aluminum alloys (Al-Mg-Si) have found considerable importance in various structural applications for their high strength to weight ratio and corrosion resistance properties. Weld defects, residual stresses, and microstructural changes are the key factors for the performance reduction as well as failure of welded structures. Tungsten inert gas (TIG/GTAW) welding was carried out on AA-6061 T651 Aluminum Alloy plates using Argon/Helium (50/50) as the shielding gas. Non-destructive phased array ultrasonic testing (PAUT) was applied for the detection and characterization of weld defects and characterization of the mechanical performances. In this study, ultrasonic technique was also used for the evaluation of post-weld residual stresses in welded components. The approach is based on the acoustoelastic effect, in which ultrasonic wave propagation speed is related to the magnitude of stresses present in the materials. To verify the estimated residual stresses by ultrasonic testing, hole-drilling technique was carried out and observed analogous results. The effects of post weld heat treatment (PWHT) on the residual stresses, grain size, micro hardness, and tensile properties were also studied. The grain size and micro hardness were studied through Heyn’s method and Vickers hardness test, respectively. Lower residual stresses were observed in post-weld heat-treated specimens, which also experienced from microstructure and micro hardness studies. The PWHT also resulted enhanced tensile properties for the redistribution of microstructures and residual stresses.
Reliability analysis of Cone Penetration Test (CPT) is very useful information for interpreting C... more Reliability analysis of Cone Penetration Test (CPT) is very useful information for interpreting CPT data. One of the identified sources of uncertainty is the inherent variation in the measurement device and equipment. This uncertainty needs to be accounted for in the reliability analysis forming the basis for the correlation of the CPT with soils engineering properties. This paper investigates the variability of CPT measurements by conducting sixteen CPT penetrations in proximity to each other to a depth of 24.4 m (80 ft). A reliability analysis is conducted to determine the coefficient of variation (COV) of q c as well as soil unit weight (γT ) and overburden pressure (σ vo). The results showed that COV qc () is higher when compared to COV (γT ) and COV(σ vo), with values close to 40% in some cases. On average, the COV for qc , γT and σ vo are 19.6%, 1.46%, and 0.51%, respectively. ABSTRACT: Reliability analysis of Cone Penetration Test (CPT) is very useful information for interpreting CPT data. One of the identified sources of uncertainty is the inherent variation in the measurement device and equipment. This uncertainty needs to be accounted for in the reliability analysis forming the basis for the correlation of the CPT with soils engineering properties. This paper investigates the variability of CPT measurements by conducting sixteen CPT penetrations in proximity to each other to a depth of 24.4 m (80 ft). A reliability analysis is conducted to determine the coefficient of variation (COV) of q c as well as soil unit weight (γT ) and overburden pressure (σ vo). The results showed that COV qc
This paper reports on a survey effort of damaged bridges conducted by the writers in the aftermat... more This paper reports on a survey effort of damaged bridges conducted by the writers in the aftermath of Hurricane Katrina of August 2005. As with Hurricane Ivan in 2004, low-lying coastal bridges suffered severe damage due to hydrodynamic forces caused by storm surge. Consequently, transportation networks in the affected areas were disrupted. Since coastal bridges are considered lifelines for the communities they serve, their loss resulted in hindering rescue and recovery efforts. The purpose of this paper is to present related data as observed by the writers. Data collection and documentation of perishable data after natural disasters and before recovery and reconstruction efforts is of great importance. In the case of coastal bridges, they can help in improving future designs and rehabilitating existing ones. The majority of the surveyed bridges collapsed due to unseating. Hydrodynamic forces due to wave impact and water current on the superstructure proved to exceed the capacity of common connections between the superstructure and the substructure for short- and medium-span bridges.
Advances in Materials and Processing Technologies, Feb 10, 2019
Friction stir welding (FSW) as a solid state joining process is being known recently by many indu... more Friction stir welding (FSW) as a solid state joining process is being known recently by many industries due to its capability to reduce defects, energy efficient, and environment friendly compared with conventional techniques. Specifically, FSW can be used to join highstrength aluminum alloys like 7XXX and 2XXX which are hard to weld by conventional fusion welding. In this review paper, the elementary principles of FSW, parameters, and the effect of the FSW parameters on microstructure and mechanical properties are addressed. Although this process has a lot of advantages compared with fusion techniques, however, many problems still remain unsolved related to poor mechanical properties of weldment's heat affected zone (HAZ). In this regard, the impact of post weld heat treatment (PWHT) on improvement of joint properties is addressed. Finally, appropriate parameters and factors for achieving the best condition of the weld is discussed.
Journal of Composites for Construction, Aug 1, 2017
AbstractRestoring the capacity of deficient structural members to meet original design requiremen... more AbstractRestoring the capacity of deficient structural members to meet original design requirements or new higher demands is common. For that purpose, research efforts to use composite materials in...
Journal of Manufacturing Science and Engineering-transactions of The Asme, Sep 4, 2015
Welding defects and the reduction of mechanical performances are the foremost problems for fusion... more Welding defects and the reduction of mechanical performances are the foremost problems for fusion welded aluminum alloys joints. The influences of weld defects and postweld heat treatment (PWHT) on tensile properties of gas tungsten arc (GTA) welded aluminum alloy AA-6061-T651 joints are investigated in this current study. All welded specimens are nondestructively inspected with phased array ultrasonic testing (PAUT) to classify weld defect and measure the projected defects area-ratio (AR). Ultimate tensile strength (UTS) decreased linearly with the increase of the size of weld defect but tensile toughness behaved nonlinearly with defect size. Depending on defect size, defective samples' joint efficiency (JE) varied from 35% to 48% of base metal's (BM) UTS. Defect-free as-welded (AW) specimens observed to have 53% and 34% JE based on UTS and yield strength (YS) of BM, respectively. PWHT was applied on defect-free welded specimens to improve tensile properties by precipitation hardening, microstructures refining, and removal of postweld residual stresses. Solution treatment (ST) (at 540 °C) followed by varying levels of artificial age-hardening (AH) time was investigated to obtain optimum tensile properties. For GTA-welded AA-6061-T651, peak aging time was 5 hr at 180 °C. PWHT specimens showed 85% JE based on UTS and up to a 71% JE based on YS of BM. However, toughness values decreased about 29% due to the presence of precipitate-free fusion zones. The experimental investigations can be used to establish weld acceptance/rejection criteria and for the design of welded aluminum alloy structures.
The International Journal of Advanced Manufacturing Technology, Nov 17, 2017
Building a reliable prediction model can mitigate the need for actual experiments, hence saving t... more Building a reliable prediction model can mitigate the need for actual experiments, hence saving time and cost. To this end, this study presents a methodology to predict weld quality for a particular friction stir weld configuration using machine learning and metaheuristic algorithms including K-nearest neighbor (KNN), fuzzy KNN (FKNN), and the artificial bee colony (ABC). The ABC algorithm was utilized to determine the best (F)KNN model with optimal K value and feature subset. First, models were built based on only experimental conditions including spindle rotational speed, plunge force, and feed rate, as well as derived values including a speed ratio and an empirical force index (EFI). The best model was identified to be 1-NN comprised of three features, i.e., rotational speed, feed rate, and EFI, with 93.16% classification accuracy based on leave-one-out cross-validation. The majority of data points leading to error were found to lie mostly on the boundaries between classes. It was shown that classification error could be reduced by removing those points, which is cheating and not recommended. Instead, it is recommended to improve classification accuracy without omitting dissenting data by introducing additional information to better distinguish misclassified data points. To this end, wavelet energy features extracted from weld signals of X-Force, Y-Force, spindle rotational speed, feed rate, and plunge force were added to the original feature pool. In order to determine the impact of each weld signal feature set, each signal feature set was individually tested. After applying ABC to the expanded feature pool to build the best model, perfect classification accuracy was achieved in several cases. The results suggest that adding signal features can greatly improve the effectiveness of model predictability of friction stir weld quality.
Acta Metallurgica Sinica (english Letters), Oct 4, 2017
This paper presents a new thermomechanical model of friction stir welding which is capable of sim... more This paper presents a new thermomechanical model of friction stir welding which is capable of simulating the three major steps of friction stir welding (FSW) process, i.e., plunge, dwell, and travel stages. A rate-dependent Johnson-Cook constitutive model is chosen to capture elasto-plastic work deformations during FSW. Two different weld schedules (i.e., plunge rate, rotational speed, and weld speed) are validated by comparing simulated temperature profiles with experimental results. Based on this model, the influences of various welding parameters on temperatures and energy generation during the welding process are investigated. Numerical results show that maximum temperature in FSW process increases with the decrease in plunge rate, and the frictional energy increases almost linearly with respect to time for different rotational speeds. Furthermore, low rotational speeds cause inadequate temperature distribution due to low frictional and plastic dissipation energy which eventually results in weld defects. When both the weld speed and rotational speed are increased, the contribution of plastic dissipation energy increases significantly and improved weld quality can be expected.
Friction stir welding (FSW) is a solid-state joining process, where joint properties largely depe... more Friction stir welding (FSW) is a solid-state joining process, where joint properties largely depend on the amount of heat generation during the welding process. The objective of this paper was to develop a numerical thermomechanical model for FSW of aluminum-copper alloy AA2219 and analyze heat generation during the welding process. The thermomechanical model has been developed utilizing ANSYS Ò APDL. The model was verified by comparing simulated temperature profile of three different weld schedules (i.e., different combinations of weld parameters in real weld situations) from simulation with experimental results. Furthermore, the verified model was used to analyze the effect of different weld parameters on heat generation. Among all the weld parameters, the effect of rotational speed on heat generation is the highest.
Journal of Composites for Construction, Nov 1, 2001
Extensive testing has shown that externally bonded carbon fiber reinforced polymer (CFRP) laminat... more Extensive testing has shown that externally bonded carbon fiber reinforced polymer (CFRP) laminates are particularly suited for improving the short-term behavior of deficient reinforced concrete beams. Accelerated fatigue tests conducted to date confirm that fatigue response is also improved. This paper describes an analytical model for simulating the static response and accelerated fatigue behavior of reinforced concrete beams strengthened with CFRP laminates. Static and fatigue calculations are carried out using a fiber section model that accounts for the nonlinear time-dependent behavior of concrete, steel yielding, and rupture of CFRP laminates. Analysis results are compared with experimental data from two sets of accelerated fatigue tests on CFRP strengthened beams and show good agreement. Cyclic fatigue causes a time-dependent redistribution of stresses, which leads to a mild increase in steel and CFRP laminate stresses as fatigue life is exhausted. Based on the findings, design considerations are suggested for the repair and/or strengthening of reinforced concrete beams using CFRP laminates.
Journal of Materials in Civil Engineering, Oct 1, 2015
Nondestructive testing (NDT) methods for identifying stress levels in materials mostly rely on th... more Nondestructive testing (NDT) methods for identifying stress levels in materials mostly rely on the theory of acoustoelasticity. However, the sensitivity and the accuracy of acoustoelasticity are affected by several factors such as the (1) type, (2) propagation, and (3) polarization directions of the used signals. This paper presents the results of an experimental investigation of longitudinal waves propagating perpendicular to the applied uniaxial tensile stresses in structural steel specimens. The changes in four ultrasonic signal characteristics were investigated with increasing stress levels ranging from below to above the yield stress of steel. The considered signal characteristics were the peak amplitudes and signal energy in the time domain, and the fast Fourier transform (FFT) and chirp-Z transform (CZT) in the frequency domain. Even though the acoustoelastic effect on the type ultrasonic signal used is very small, clear distinctions between prior to and postyielding are observed for all investigated parameters. The results are presented with a detailed statistical and receiver operating characteristics (ROCs) analyses. The results show that identifying damage to steel structures due to local yielding is possible using the simple ultrasonic signal classification.
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Papers by Ayman M Okeil