Mechanical Properties of Aircraft Materials Subjected to Long Periods of Service Usage

1997 ◽  
Vol 119 (4) ◽  
pp. 380-386 ◽  
Author(s):  
J. N. Scheuring ◽  
A. F. Grandt
Keyword(s):  
Tensile Stress ◽  
Crack Growth ◽  
Cyclic Stress ◽  
Primary Objective ◽  
Material Behavior ◽  
Fatigue Properties ◽  
Virgin Material ◽  
Service Usage ◽  
Stress Strain ◽  
Effects Of Aging

This paper evaluates changes in the behavior of aircraft materials which result from aging and/or corrosion that occurs during long periods of service usage. The primary objective was to determine whether damage tolerant analyses for older aircraft should employ updated properties that more accurately represent the current state of the material, or if the virgin material properties continue to properly characterize the aged/corroded alloy. Specifically, tensile stress-strain curves, cyclic stress life (SN) tests, and fatigue crack growth tests were used to characterize the “aged aircraft” material. These properties were compared with handbook properties for virgin material of the same pedigree. The aluminum alloys tested were obtained from fuselage and wing panels of retired KC-135 aircraft. Computer controlled tests were conducted using specimens machined from the retired aircraft components. Different configurations were used to observe the effects of aging and/or corrosion on material behavior. In the crack growth specimens, various levels of corrosion were observed, thus the crack growth rates could be categorized as a function of the level of corrosion present. The SN and da/dN-ΔK curves for the “aged” only materials were compared with the fatigue properties of virgin material of the same alloy. Similar comparisons were performed for the tensile stress-strain properties.

The Influences of Cutting Speed on the Fatigue of Titanium Alloy

2007 ◽  
Vol 10-12 ◽  
pp. 742-746
Author(s):  
Guo Sheng Geng ◽  
Jiu Hua Xu
Keyword(s):  
Titanium Alloy ◽  
Electron Microscope ◽  
High Speed ◽  
Cutting Speed ◽  
Cyclic Stress ◽  
Fatigue Properties ◽  
Stress Strain ◽  
Ta15 Titanium Alloy ◽  
Cutting Speeds ◽  
Scanning Electron

This research is concerned with the influences of cutting speed on the fatigue properties of high speed milled Ti-6.5Al-2Zr-1Mo-1V (TA15) titanium alloy. Four different cutting speeds ranging from 50 to 200m/min were used to mill the specimens for fatigue test, and the fatigue properties of them were studied at two stress levels: 80—800MPa and 90—900MPa. The fatigue lives of the specimens milled under different cutting speeds were compared. The fracture surfaces were analyzed using scanning electron microscope (SEM), and cyclic stress-strain properties of TA15 titanium alloy were investigated with a stress-strain gauge. The results showed that increasing cutting speed can help to improve the fatigue properties of titanium alloy, especially at a relatively low cyclic stress level.

Tensile Stress—Strain Measurements for Characterization of Gum Elastomers and Filled Compounds

1990 ◽  
Vol 63 (4) ◽  
pp. 624-636 ◽  
Author(s):  
N. Nakajima ◽  
M. H. Chu ◽  
R. Babrowicz
Keyword(s):  
Shear Modulus ◽  
Tensile Stress ◽  
Shear Deformation ◽  
Tensile Modulus ◽  
Nonlinear Behavior ◽  
Material Behavior ◽  
Structural Constraints ◽  
Stress Strain ◽  
Strain Measurements ◽  
Diene Rubbers

Abstract For a gum elastomer in its amorphous, isotropic state, shear modulus and tensile modulus are related with a factor of three. This relation is maintained in the range of temperature and time scale defining the rubbery region of the material behavior. When a large deformation is imposed, for example, in tensile stress—strain measurements, the above relation may still be preserved, if the nonlinear behavior can be linearized. The strain—time correspondence principle is the linearization scheme of this work. When a gum elastomer contains various structural constraints, the factor three relation does not apply, even after the application of the above linearization scheme. Example of constraints are excessive amounts of long branches, gel, molecular associations, and reinforcing fillers. These constraints usually make the factor larger than three. This is because the constraints make the large, elongational deformation more difficult to achieve compared to shear deformation. An example of gum elastomer in this work is a polyethylacrylate containing a significant amount of gel. With this polymer, both the presence of gel and the molecular association act as the constraints. However, when 50 phr of carbon blacks are added, the fillers do not act as strong constraints as they do when they are in the diene rubbers. This is because the polyethylacrylate is known to have a weaker affinity to carbon black compared to the diene rubbers. Triblock copolymers, styrene—isoprene—styrene, were examined according to the above treatment; 25% polystyrene copolymer exhibited crosslink-like behavior by the polystyrene domains. However, 14% polystyrene copolymers acted as if they are no crosslinks. When these copolymers are diluted to 44% with an addition of 56% tackifier, the ratio of tensile to shear modulus became less than three. The styrene domains must have effective crosslinks at the small shear deformation, but at large tensile deformations such crosslinks must not be present.

The Effects of Aging of the Cyclic Stress-Strain and Fatigue Behaviors of Lead Free Solders

2013 ◽  
Author(s):  
Muhannad Mustafa ◽  
Jordan C. Roberts ◽  
Jeffrey C. Suhling ◽  
Pradeep Lall
Keyword(s):  
Cyclic Loading ◽  
Damage Accumulation ◽  
Solder Joints ◽  
Peak Load ◽  
Cyclic Stress ◽  
Lead Free ◽  
Failure Behavior ◽  
Stress Strain ◽  
Effects Of Aging ◽  
Lead Free Solders

Solder joints in electronic assemblies are typically subjected to thermal cycling, either in actual application or in accelerated life testing used for qualification. Mismatches in the thermal expansion coefficients of the assembly materials cause the solder joints to be subjected to cyclic (positive and negative) mechanical strains and stresses. This cyclic loading leads to thermomechanical fatigue damage that involves damage accumulation, crack initiation, crack propagation, and failure. In addition, the microstructure, mechanical response, and failure behavior of lead free solder joints in electronic assemblies are constantly evolving when exposed to isothermal aging and/or thermal cycling environments. While the effects of aging on solder constitutive behavior (stress-strain and creep) have been examined in some detail, there have been no prior studies on the effects of aging on solder failure and fatigue behavior. Aging leads to both grain and phase coarsening, and can cause recrystallization at Sn grain boundaries. Such changes are closely tied to the damage that occurs during cyclic mechanical loading. In this investigation, we have examined the effects of aging on the cyclic stress-strain behavior and fatigue life of lead free solders. Uniaxial solder test specimens (SAC105 and SAC305) have been prepared and subjected to cyclic stress/strain loading at different aging conditions. A four-parameter hyperbolic tangent empirical model has been used to fit the entire cyclic stress-strain curve and the hysteresis loop size (area) was calculated using definite integration for a given strain limit. This area represents the energy dissipated per cycle, which is correlated to the damage accumulation in the joint. Using the recorded cyclic stress-strain curves, the evolution of the solder hysteresis loops with aging have been characterized and empirically modeled. Similar to solder stress-strain and creep behavior, there is a strong effect of aging on the hysteresis loop size (and thus the rate of damage accumulation) in the solder specimens. Fatigue experiments were also performed, where the uniaxial specimens were subjected to cyclic loading over a particular strain range until failure. Fatigue failure in the experiments was defined to occur when there was a 50% peak load drop during mechanical cycling. Prior to testing, the specimens were aged (preconditioned) at 125 °C for various aging times, and then the samples were subjected to cyclic loading at room temperature (25 °C). It was found that aging decreased the mechanical fatigue life, and the effects of aging on the peak load drop have been studied. It has also been observed that degradations in the fatigue/failure behavior of the lead free solders with aging are highly accelerated for lower silver content alloys (e.g., SAC105). Various empirical failure criteria such as the Coffin-Manson model and the Morrow model have been used to fit the measured data, and the parameters in the models have been determined as a function of the aging conditions.

Cyclic Stress-Strain and Fatigue Properties of Sheet Steel as Affected by Load Spectra

1983 ◽  
Vol 11 (1) ◽  
pp. 66 ◽  
Author(s):  
R Horstman ◽  
KA Peters ◽  
RL Meltzer ◽  
M Bruce Vieth ◽  
JF Martin
Keyword(s):  
Sheet Steel ◽  
Cyclic Stress ◽  
Fatigue Properties ◽  
Stress Strain ◽  
Load Spectra

Characterization of High Temperature Thermomechanical Fatigue Properties for Particle Reinforced Composites

2005 ◽  
Vol 297-300 ◽  
pp. 1495-1502
Author(s):  
Hui Ji Shi ◽  
Ya-Xiong Zheng ◽  
Ran Guo ◽  
Gerard Mesmacque
Keyword(s):  
Finite Element ◽  
Fatigue Behavior ◽  
Voronoi Cell ◽  
Thermomechanical Fatigue ◽  
Cyclic Stress ◽  
Fatigue Properties ◽  
Reinforced Composites ◽  
Interfacial Damage ◽  
Stress Strain ◽  
Particle Reinforced Composites

Voronoi cell finite element method (VCFEM) is introduced in this paper to describe the elastic-plastic-creep behavior of particle reinforced composites. The interfacial damage is simulated by partly debonding between Matrix and inclusion. A validation of the nonlinear behavior of the cell element has been carry out by comparing VCFEM results with those calculated by the general finite element package MARC and ABAQUS, and good agreements are found. A microstructure with five inclusions is taken as an example to describe the cyclic stress-strain behavior under different particulate orientation condition, and it shows the influence of the topological microstructure of inclusions. Thermomechanical fatigue properties are also investigated and the loops of stress-strain show the great differences of fatigue behavior between the in-phase case and out-of-case.

Critical Entropy Threshold: An Irreversible Thermodynamic Theory of Fatigue

2012 ◽  
Author(s):  
P. W. Whaley
Keyword(s):  
Fatigue Damage ◽  
Fatigue Testing ◽  
Tensile Tests ◽  
Cyclic Stress ◽  
Irreversible Thermodynamic ◽  
Fatigue Properties ◽  
Microplastic Deformation ◽  
Polycrystalline Materials ◽  
Model Parameters ◽  
Stress Strain

A theoretical model for material fatigue is described using irreversible thermodynamics to quantify fatigue damage by the generation of microplastic entropy. The microplastic entropy generated quantifies the microplastic deformation, commonly accepted as the mechanism of fatigue damage in polycrystalline materials. A stochastic model for microplastic deformation is utilized to calculate the expected values of tensile stress–strain, cyclic stress–strain, microplastic strain energy density and the microplastic entropy generated. When the cumulative microplastic entropy generated in cyclic loading exceeds the critical microplastic entropy threshold calculated from tensile tests, failure occurs. Calculated fatigue life with 99% tolerance limits (99% confidence) compares favorably to data for 6061-T6 aluminum rod and sheet specimens. Model parameters are determined from tensile tests and simple cyclic tests, decreasing the high cost of fatigue testing for parameter identification. This new theory has the potential to significantly decrease the cost of characterizing the fatigue properties of new materials.

Effect of Technologies Processing on Material Properties of Selected Aluminium Alloys

2014 ◽  
Vol 782 ◽  
pp. 394-397
Author(s):  
Petra Lacková ◽  
Daniela Žabecká ◽  
Ondrej Milkovič ◽  
Milan Škrobian ◽  
Matúš Bajcura
Keyword(s):  
Mechanical Properties ◽  
Tensile Stress ◽  
Material Properties ◽  
Aluminium Alloys ◽  
Natural Aging ◽  
Cyclic Stress ◽  
Fatigue Properties ◽  
Solution Annealing ◽  
Cold Forming ◽  
Condition Solution

The paper is concerned with an analysis of utility properties of selected aluminium alloys, namely EN AW 6082 (AlSi1MgMn), EN AW 6061 (AlMg1SiCu) and EN AW 7075 (AlZn5.5MgCu) with different technology of hot processing. The alloys were hot processed to reach T3 condition (solution annealing, cold forming and natural aging) and to reach T4 condition (solution annealing and natural aging). The following parameters were subject to evaluation: microstructure and sub-structure, mechanical properties (strength and plastic characteristics stated in Table. 1) as well as fatigue properties of these alloys assessed during alternative symmetrical stress in torsion. The paper was aimed to study the affect of processing technology of three aluminium alloys on their utility properties in the conditions of tensile stress and cyclic stress in torsion.

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