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Technical Paper

Fatigue Failures of Spot Friction Welds in Aluminum 6111-T4 Sheets Under Cyclic Loading Conditions

2006-04-03
2006-01-1207
Fatigue failures of spot friction welds in lap-shear specimens of aluminum 6111-T4 sheets under cyclic loading conditions are investigated in this paper. The paths of fatigue cracks near the spot friction welds are first discussed. A fatigue crack growth model based on the Paris law for crack propagation and the global and local stress intensity factors for kinked cracks is then adopted to predict the fatigue lives of these spot friction welds. The global stress intensity factors and the local stress intensity factors based on the recent published works for resistance spot welds in lap-shear specimens are used to estimate the local stress intensity factors for kinked cracks with experimentally determined kink angles. The results indicate that the fatigue life predictions based on the Paris law and the local stress intensity factors as functions of the kink length agree well with the experimental results.
Technical Paper

Honeycomb Specimens Under Combined Compressive and Shear Displacement Conditions

2005-04-11
2005-01-0360
The quasi-static crush behavior of aluminum 5052-H38 honeycomb specimens under non-proportional compression dominant combined loads is investigated by experiments. Compression dominant combined loads and pure compressive loads were applied in different sequences to induce non-proportional combined loads. The experimental results show that the normal crush and shear strengths in combined loading regions and the normal crush strengths in pure compressive loading regions of the non-proportional combined loads are quite consistent with the existing phenomenological yield criterion based on the experimental normal crush and shear strengths under proportional combined loads. The experimental results indicate that the sequence of loading paths for the non-proportional combined loads does not affect the crush strengths of honeycomb specimens.
Technical Paper

Effects of Impact Velocity on Crush Behavior of Honeycomb Specimens

2004-03-08
2004-01-0245
Effects of impact velocity on the crush behavior of aluminum 5052-H38 honeycomb specimens are investigated by experiments. An impact test machine using pressurized nitrogen was designed to perform dynamic crush tests. A test fixture was designed such that inclined loads can be applied to honeycomb specimens in dynamic crush tests. The results of dynamic crush tests indicate that the effects of impact velocity on the normal and inclined crush strengths are significant. The trends of the inclined crush strengths for specimens with different in-plane orientation angles as functions of impact velocity are very similar to that of the normal crush strength. Experimental results show similar progressive folding mechanisms for honeycomb specimens under pure compressive and inclined loads. Under inclined loads, the inclined stacking patterns were observed. The inclined stacking patterns are due to the asymmetric locations of the horizontal plastic hinge lines.
Technical Paper

Modeling of Diesel Combustion and NO Emissions Based on a Modified Eddy Dissipation Concept

2004-03-08
2004-01-0107
This paper reports the development of a model of diesel combustion and NO emissions, based on a modified eddy dissipation concept (EDC), and its implementation into the KIVA-3V multidimensional simulation. The EDC model allows for more realistic representation of the thin sub-grid scale reaction zone as well as the small-scale molecular mixing processes. Realistic chemical kinetic mechanisms for n-heptane combustion and NOx formation processes are fully incorporated. A model based on the normalized fuel mass fraction is implemented to transition between ignition and combustion. The modeling approach has been validated by comparison with experimental data for a range of operating conditions. Predicted cylinder pressure and heat release rates agree well with measurements. The predictions for NO concentration show a consistent trend with experiments. Overall, the results demonstrate the improved capability of the model for predictions of the combustion process.
Technical Paper

Failure Mechanisms of Sandwich Specimens With Epoxy Foam Cores Under Bending Conditions

2003-03-03
2003-01-0327
Sandwich specimens with DP590 steel face sheets and structural epoxy foam cores are investigated under three-point bending conditions. Experimental results indicate that the maximum loads correspond to extensive cracking in the foam cores. Finite element simulations of the bending tests are also performed to understand the failure mechanisms of the epoxy foams. In these simulations, the plastic behavior of the steel face sheets is modeled by the Mises yield criterion with consideration of plastic strain hardening. A pressure sensitive yield criterion is used to model the plastic behavior of the epoxy foam cores. The epoxy foams are idealized to follow an elastic perfectly plastic behavior. The simulation results indicate that the load-displacement responses of some sandwich specimens agree with the experimental results.
Technical Paper

Crush Strength of Aluminum 5052-H38 Honeycomb Materials under Combined Compressive and Shear Loads

2003-03-03
2003-01-0331
The crush strength of aluminum 5052-H38 honeycomb materials under combined compressive and shear loads are investigated here. The experimental results indicate that both the peak and crush strengths under combined compressive and shear loads are lower than those under pure compressive loads. A yield function is suggested for honeycomb materials under the combined loads based on a phenomenological plasticity theory. The microscopic crush mechanism under the combined loads is also investigated. A microscopic crush model based on the experimental observations is developed. The crush model includes the assumptions of the asymmetric location of horizontal plastic hinge line and the ruptures of aluminum cell walls so that the kinematic requirement can be satisfied. In the calculation of the crush strength, two correction factors due to non-associated plastic flow and different rupture modes are considered.
Technical Paper

Influence of Shear Loads on Crush of Honeycomb Materials

2002-03-04
2002-01-0683
We conduct static experiments to investigate the influence of shear stress on the crush behavior of honeycomb materials. The aluminum honeycomb materials selected in this investigation are orthotropic due to their manufacturing processes. A test fixture and honeycomb specimens are designed such that combined compressive and shear loads along the strongest material symmetry axis can be controlled and applied accurately. The experimental results indicate that both the peak and crush strengths under combined compressive and shear loads are lower than those under pure compressive loads. A yield function is suggested for honeycomb materials under the combined loads based on a phenomenological plasticity theory. The microscopic crush mechanism under the combined loads is also investigated. A microscopic crush model based on the experimental observations is developed. The crush model includes the rupture of aluminum cell walls so that the kinematic requirement can be satisfied.
Technical Paper

Modeling and Testing of Spot Welds under Dynamic Impact Loading Conditions

2002-03-04
2002-01-0149
Failure behavior of spot welds is investigated under impact loading conditions. Three different impact speeds were selected to test both HSLA steel and mild steel specimens under combined opening and shear loading conditions. A test fixture was designed and used to obtain the failure loads of spot weld specimens of different thicknesses under a range of combined opening and shear loads with different impact speeds. Accelerometers were installed on the fixtures and the specimens for investigation of the inertia effects. Optical micrographs of the cross sections of failed spot welds were obtained to understand the failure processes in both HSLA steel and mild steel specimens under different combined impact loads. The experimental results indicate that the failure mechanisms of spot welds are very similar for both HSLA steel and mild steel specimens with the same sheet thickness. These micrographs show that the sheet thickness can affect the failure mechanisms.
Technical Paper

Failure of Laser Welds in Aluminum Sheets

2001-03-05
2001-01-0091
In this paper, the formability of AA5754 aluminum laser-welded blanks produced by Nd:YAG laser welding is investigated under biaxial straining conditions. The mechanical behavior of the laser-welded blanks is first examined by uniaxial tensile tests conducted with the weld line perpendicular to the tensile axis. Shear failure in the weld metal is observed in the experiments. Finite element simulations under generalized plane strain conditions are then conducted in order to further understand the effects of weld geometry and strength on the shear failure and formability of these welded blanks. The strain histories of the material elements in the weld metal obtained from finite element computations are finally used in a theoretical failure analysis based on the material imperfection approach to predict the failure strains for the laser-welded blanks under biaxial straining conditions.
Technical Paper

Plane-Strain Tension Tests of Al 2008-T4 Sheets

1993-03-01
930812
Rectangular aluminum sheets were stretched under in-plane plane-strain tension using a simple experimental setup. The samples can be stretched under these conditions until localized necking occurs at the centerline. The strain distributions and the loads were recorded at different strain levels. Good agreement was found between actual loads and those calculated from strain measurements assuming isotropic hardening with a high exponent yield criterion.
Technical Paper

Slip Resistance Predictions for Various Metal Step Materials, Shoe Soles and Contaminant Conditions

1987-11-01
872288
The relationship of slip resistance (or coefficient of friction) to safe climbing system maneuvers on high profile vehicles has become an issue because of its possible connection to falls of drivers. To partially address this issue, coefficients of friction were measured for seven of the more popular fabricated metal step materials. Evaluated on these steps were four types of shoe materials (crepe, leather, ribbed-rubber, and oil-resistant-rubber) and three types of contaminant conditions (dry, wet-water, and diesel fuel). The final factor evaluated was the direction of sole force application. Results showed that COF varied primarily as a function of sole material and the presence of contaminants. Unexpectedly, few effects were attributible to the metal step materials. Numerous statistical interactions suggested that adequate levels of COF are more likely to be attained by targeting control on shoe soles and contaminants rather than the choice of a particular step material.
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