Engineering and Technology Journal

The present study described the effect of shot peening on mechanical properties and rotating corrosion –fatigue behavior (strength and life) of AA6061-T6. Ultimate tensile strength (UTS) and yield stress (YS) were reduced by 4.6% and 1.24% when immersing the tensile samples in crude oil for 60 days. The values of (UTS) and (YS) were raised from 307 to 316 MPa and from 248 to 254 MPa respectively when treated for 10 min. shot peening (SP). Hardness of oil corrosion samples dropped due to pitting corrosion and slightly raised for SP prior to corrosion samples. Oil corrosion reduced the fatigue strength by (-1.25%). This percentage was enhanced due to SP to 2.377%. SP significantly increased the rotating fatigue life by a factor of 1.19 and 1.3 at (UTS) and (Ys) loads respectively. (SP) technique improved corrosion-fatigue resistance due to producing compressive residual stresses at surface layers.

Fatigue analysis helps in predicting life of the component and seeks improvements of the whole process in design phase. Efforts are continually made to combat the fatigue phenomenon, yet certain mechanical components are still failing due to fatigue. The present work proposes a laminated design of beams, which undergo fatigue. The well-known Paris-Erdogan formula was used to theoretically predict fatigue life of the proposed design. The design was shown to enhance fatigue properties through laminating the cross section of the component; Barriers in front of a propagating crack is deliberately included by lamination. Spectacular levels of improvement in the fatigue life of up to 102% were achieved by replacing the monolithic type by only seven laminates. The present analysis was proved efficient in verifying the anticipated improvement acquired by the proposed design of laminated beams.

Laser peening (LP) is a surface treatment technology for metallic materials. LP has shown agreat improvement in the fatigue strength and life.A study of fatigue under constant rotating bending stress programs has been conducted on 7049 AL alloy at a stress ratio (R=-1) and room temperature using laser peening technique .Four groups of tests have been designed.The first group (15 specimens) tested under unpeened condition. The second group (15 specimens) tested under air laser peening (ALP) while the third group (15 specimens) tested under water laser peening (WLP). The last group was designed to examine the fatigue behavior under black paint laser peening (BPLP). All the above groups were designed to establish the S-N curve. The results show no effect of laser peening LP at higher stresses (above 300 MPa), while this effect appears clearly at low stresses (200 and 250 MPa). The results alsoindicated that the WLP is more effective than the ALP. The fatigue life improvement factor (FLIF%) was 39, 18.9 and 4.65 under WLP for 200 MPa, 250 MPa and 300 MPa stress levels respectively.while a clear effect was observed for black paint laser peening (BPLP),it was found that the FLIF % was 93.25 at 300 MPa , 103.24 at 250 MPa and 116 at 200 MPa compared to unpeened data .

The present work is aimed to study the fatigue behavior of friction stir welding for the similar and dissimilar joints taking into account the effects of welding position, post welding heat treatments, and surface roughness. The materials were used AA2024T3 and AA6061T6. The maximum welding efficiency achieved at friction stir welding process was 62.8 % of the base metal for the similar 2024-T3 joint, and this value was improved by using post welding heat treatments and reach to 67.9%. Results showed that fatigue strength at 106 cycles depended strongly on welding line position where for welding line at a distance 0.35L from loading side, the reduction in fatigue limit with respect to 2024T3 base material was 45% for similar joint and 58% for dissimilar joints, and for welding line at a distance 0.7 L, the reduction in fatigue strength was 56% for similar joint and 67% for dissimilar joints. While, it was a large reduction in the fatigue strength reaching to 70% in both similar and dissimilar joint for the welding joint at a distance L (i.e at the fixing end). The heat treatments improved the fatigue strength about 31% more than non heat treatments of the similar 2024T3 joint by fsw at 0.7L in high cycle regime. Finally, the non-finishing samples showed a reduction in fatigue strength reaching to 10% more than the finishing samples of the similar 2024T3 joint at 0.7L.

The purpose of this study is to evaluate the effect of hydrated lime addition methods as filler replacement on fatigue performance of Hot Mix Asphalt (HMA). Three types of addition methods of hydrated lime were introduced namely dry HL on dry aggregate and saturated surface aggregate above 3% and slurry HL on dry aggregate, ordinary Lime stone powder was reduced by three HL percentage (1.0, 2.0 and 3.0 %). The effect of different methods were investigated on the fatigue properties of HMA using, third-point flexural fatigue bending Test. Pneumatic Repeated Load System (PRLS) was carried out to establish the effect of hydrated lime on the fatigue failure criteria and to select the proper hydrated lime application methods on fatigue behavior of HMA mixtures. The fatigue functions for asphalt mixture with hydrated lime are obtained and compared, and it confirm that the fatigue property of asphalt mixture can be improved using all methods and the addition methods were exhibited different optimality for the result due to its effect . The test results were carried out through the performance analysis using Vesys 5W (2003) to study the long term effectiveness of hydrated lime effect.

A mechanism of crack growth was investigated in resistance spot welds of mild
steel. The experiments in this study were designed to investigate the effects of the
electrode cap geometrieson fatigue life of the resistance spot weld specimens. Two
types of electrode cap geometries were used. These types are 4.8 mm and 6.3 mm
nose,used with the same shank in welding operations of 2mm mild steel plate. To
obtain the goal, operating factors were precisely controlled, especially the electrode
force and welding current of spot welds, to keep the same operating conditions while
changingthe electrode geometries. The life test results showed an improvement in the
fatigue life of resistance spot welds. The increment was 30% in heavy loads and 10%
in low loads based on tool geometry. The improvement in the fatigue life was
produced by reducing the diameter of the nose in the geometry of the tool.

Mechanical properties were investigated in base and friction stir linear welds of 7075 aluminum alloy. Welding tools consist of a shoulder with a pin and with-out pin. This work addresses the effects of tool geometry on tensile stress and shear strength of butt and lap welds, and comparing with base material. Also, the effects of process condition on the strength of friction stir processed material are quantitatively characterized. Compared to the butt case, the friction stir lap linear welds, with pin, leads to a 20% increase in optimized weld strength with 1000 rpm of tool revolutions and 200 mm/min of tool speed. The optimizing of operating conditions primarily leads to a 15% increase in optimized weld shear strength, with 1000 rpm of tool revolutions and 200 mm/min of tool speed.

Knee ankle foot orthoses (KAFOs) are prescribed to paraplegic patients with low level spinal cord injury and with good control of the trunk muscles. Three types of KAFOs were used in this work (plastic-metal, metal-metal and composite materials), the composite materials were depended on the number of perlon layers (13 layers & 9 layers) with one layer of carbon-fiber and (6 layers) without carbon-fiber. The mechanical properties of most of the KAFOs’ materials were tested by tensile test and fatigue machines.
The data of gait cycle (Ground Reaction Force (GRF), and pressure distribution) were collected from one patient with poliomyelitis (wearing brace type KAFO) and one normal subject. In this paper, the FEM (ANSYS) was used to compute the safety factor of fatigue for all types of KAFOs’ models and the equivalent stress (Von-Mises). The interface pressure between the patient’s leg and the brace was tested by using a piezoelectric sensor.
The results obtained from ANSYS gave the profile of safety factor of fatigue, for metal-metal KAFO (3.69), plastic-metal model (0.88). While, the (13) layers for composite material was about (1.4), but (1.07) & (0.41) for (9) layers and (6) layers, respectively. The value of safety factor increased with the composite material for the suggested design.

The objective of this work is to investigate the salt water effects on fatigue
degradation, and stress-life relationship. A series of reversed fatigue experiments were
conducted on (carbon+ glass) / PMMA of salt water environments. Results indicate that
the composite degrade during cycling. Exposure to salt water (salt water is used to
simulate the sea water) provides the most significant reduction in fatigue life. The
corrosion environment reduces the fatigue strength by 61% compared to dry fatigue.
Based on previous damage model [16], corrosion – fatigue nonlinear damage model is
presented in this paper, which contains one material constant; the inverse slope (α) of the
S-N curve. Six specimens of two levels loading of composite material were used to verify
the present model; the results showed that the predicted life is in good agreement with the
experimental results.

The seismic response of the nuclear tower is analyzed by investigating the frequency response during the main recorded events. The dynamic characteristics of the nuclear tower under seismic response with higher intensity are pointed out the dominant seismic time history components determines the response characteristics of the tower. The nuclear tower coupled with the seismic loadings will amplify the damages to
the structure. These results are consistent with field observations after major seismic response, this explains the symmetry of the nuclear tower damage during seismic response. Seismic resistance measures, such as viscous damping or energy dissipation, dynamic properties and nuclear tower vibration elements will help to increase the
accuracy of the life model. In this paper, improvement in using computing program and mathematical algorithms will increase both the accuracy and confidence of the results. The contact problem of the nuclear tower structure is another direction for a detailed understanding the mechanism of the nuclear tower structure interaction, such as mode shapes, eigenvalues/vectors, deformation, propagation and non-propagation of cracks, and the stresses slip of the foundation caused by random seismic loading that can lead to damage. This study is helpful for designing new seismic resistant nuclear towers structures to reduce damage.

In the present work the effect of residual stress on the fatigue behavior of
2024 Aluminum alloy was studied experimentally and numerically using
finite element method with aid of ANSYS-11 software. All the test
specimens treated by annealing before any process to remove the internal
stresses due to cold work. Residual stresses were imparted to the fatigue tests
specimens by heat treatment, pre-strain and welding. X-Ray diffraction was
used to measure the residual stress.
The heat treatment; done on the test specimens with different temperature of
(420, 450, 480, and 510) oC. After heat treatment; alloy mechanical properties
were improved. For the heat treated specimens as the temperature increased
the compressive residual stress increased to (27.06, 41.43, 72.8 and 85.6)
MPa. That leads to increase the endurance fatigue limit by (32.93%, 40.48%,
50.68% and 61.03%) respectively than other alloy as received. While in pre
strain groups; the test specimens loaded to (265, 290, 315 and 340) MPa by a
tension test machine. As the applied load series were increased the
compressive residual stress increased to (16.51, 25.62, 51.54 and 62.44) MPa
which improve the endurance fatigue limit by (7.68%, 16.19%, 24.98%, and
46.45%), respectively. An electrical arc and metal inert gas were used in
welding series to weld the test specimens, that present a tensile residual stress
of (76.93 and 72.66) MPa, which reduces the endurance fatigue limit by
(23.45% and 16.08%), respectively. The numerical results present fatigue
behavior, deflection and stress at any load, and show a reasonable agreement
results with an experimental one.

This research illustrates the influence of different heat treatments on the mechanical properties such as stress-strain curves ,wear resistance and fatigue properties of medium carbon steel,. This steel was treated by annealing, normalizing, hardening followed by tempering and laser treatments. The bulk mechanical properties of ultimate ,fracture and yield tensile strength were evaluated. Surface mechanical properties of fatigue, wear resistance and hardness were evaluated as well. Microstructure of treated alloys also were inspected. Results showed that (hardened -tempered) steel had improved tensile strength,
fatigue{limit, life}, wear resistance, hardness then laser surface treated alloy, then the normalized alloy came in order ,but annealed alloy had the lowest mechanical properties. Annealing caused softening and growth of alloy structure. It was found that the microstructure of treated alloy play an important role in the improvement
or deterioration of bulk and surface mechanical properties and by analyzing the obtained results. For (Quenched -tempered) alloy found fine tempered martensititic structure, laser surface treated alloy had martensititic structure in the skin and ferritic- pearlitic structures in the core .Normalized alloy had ferriticpearlitic structures, Annealed alloy had coarse ferritic- pearlitic structures

In some applications, the aluminum alloy 2024 T4 may be subjected to an
interaction of fatigue and creep effects at high temperature. This paper investigates
the effect of this interaction by studying the effect of constant amplitude fatigue
(CAF) and creep separately, and then fatigue-creep interaction is introduced by
testing the alloy under constant amplitude with some holding time periods through
the test at high temperature (150 oC). The results showed that the life time of the
alloy decreases due to fatigue-creep interaction as compared to creep alone in
about 77%, and in about 80% as compared with fatigue alone. This is a result of
accumulated fatigue damage superimposed on creep damage. Creep allows more
free spaces for fatigue cracks paths that accelerate failure. A theoretical model to
calculate the time to failure due to fatigue-creep interaction has been proposed.
This theoretical interaction model predicts very close time to failure values to the
experimental results.

This study is concerned with the effect of heat treatment (precipitation
hardening) on notch sensitivity factor for aluminum alloy (7075). Tests were
conducted on four configurations of specimens, three of them which had external
circumferential notches with notch radii of 0.5 mm, 0.7 mm, and 1 mm. The
fourth configuration is un-notched specimens. The alloy samples which were used
in fatigue test were subjected to cold working before heat treatment. Dimensions
and roughness of the specimens were measured. The fatigue tests were performed
for different types of specimens. The (S-N) equation was derived for each group to
estimate the fatigue life under any applied stress amplitude. In addition, the
strength reduction factor (kf )and notch sensitivity factor (q) were calculated.
The results showed that the fatigue strength reduction factor were
increased after heat treatment and with decreasing notch radius. Also the notch
sensitivity factor increased with increasing notch radius and after heat treatment.
The enhancement percentage in notch sensitivity factor after the heat treatment for
1 mm radius notch was (22.616%).