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Journal Article

Effect of Surface Roughness and Lubrication on Scuffing for Austempered Ductile Iron (ADI)

2015-04-14
2015-01-0683
This paper describes the scuffing tests performed to understand the effect of surface roughness and lubrication on scuffing behavior for austempered ductile iron (ADI) material. As the scuffing tendency is increased, metal-to-metal interaction between contacting surfaces is increased. Lubrication between sliding surfaces becomes the boundary or mixed lubrication condition. Oil film breakdown leads to scuffing failure with the critical load. Hence, the role of surface roughness and lubrication becomes prominent in scuffing study. There are some studies in which the influence of the surface roughness and lubrication on scuffing was evaluated. However, no comprehensive scuffing study has been found in the literature regarding the effect of surface roughness and lubrication on scuffing behavior of ADI material. The current research took into account the inferences of surface roughness and lubrication on scuffing for ADI.
Technical Paper

Measure of Forming Limit Strain on the Aluminum Sheets Passed Through Draw-Bead by Digital Image Correlation

2015-04-14
2015-01-0598
Accurate determination of the forming limit strain of aluminum sheet metal is an important topic which has not been fully solved by industry. Also, the effects of draw beads (enhanced forming limit behaviors), normally reported on steel sheet metals, on aluminum sheet metal is not fully understood. This paper introduces an experimental study on draw bead effects on aluminum sheet metals by measuring the forming limit strain zero (FLD0) of the sheet metal. Two kinds of aluminum, AL 6016-T4 and AL 5754-0, are used. Virgin material, 40% draw bead material and 60% draw bead material conditions are tested for each kind of aluminum. Marciniak punch tests were performed to create a plane strain condition. A dual camera Digital Image Correlation (DIC) system was used to record and measure the deformation distribution history during the punch test. The on-set necking timing is determined directly from surface shape change. The FLD0 of each test situation is reported in this article.
Technical Paper

Measurement of Aluminum Edge Stretching Limit Using 3D Digital Image Correlation

2015-04-14
2015-01-0594
This paper introduces an industrial application of digital image correlation technique on the measurement of aluminum edge stretching limit. In this study, notch-shape aluminum coupons with three different pre-strain conditions are tested. The edge stretching is proceeded by standard MTS machine. A dual-camera 3D Digital Image Correlation (DIC) system is used for the full field measurement of strain distribution in the thickness direction. Selected air brush is utilized to form a random distributed speckle pattern on the edge of sheet metal. A pair of special optical lens systems are used to observe the small measurement edge area. From the test results, it demonstrate that refer to the notched coupon thickness, pre-tension does not affect the fracture limit; refer to the virgin sheet thickness, the average edge stretch thinning limits show a consistent increasing trend as the pre-stretch strain increased.
Technical Paper

The Research on Edge Tearing with Digital Image Correlation

2015-04-14
2015-01-0593
Material formability is a very important aspect in the automotive stamping, which must be tested for the success of manufacturing. One of the most important sheet metal formability parameters for the stamping is the edge tear-ability. In this paper, a novel test method has been present to test the aluminum sheet edge tear-ability with 3D digital image correlation (DIC) system. The newly developed test specimen and fixture design are also presented. In order to capture the edge deformation and strain, sample's edge surface has been sprayed with artificial speckle. A standard MTS tensile machine was used to record the tearing load and displacement. Through the data processing and evaluation of sequence image, testing results are found valid and reliable. The results show that the 3D DIC system with double CCD can effectively carry out sheet edge tear deformation. The edge tearing test method is found to be a simple, reliable, high precision, and able to provide useful results.
Technical Paper

A Technique for Cargo Box Tailgate CAE Fatigue Life Predictions Loaded with Inertial Forces and Moments

2015-04-14
2015-01-0532
This paper describes a CAE fatigue life prediction technique for a tailgate on pickup truck cargo box with inertial forces and moments applied at mass center of the tailgate as input loads. The inertial forces and moments are calculated from the accelerations measured at the corners of the tailgate as the truck is being driven over a durability schedule at the test proving grounds. All the dynamic responses of the tailgate on cargo box, including any dynamic interactions at the pivot joints between the tailgate and box sides, are captured in the acquired data and also in the inertial forces and moments computed at the mass center. Correspondingly, all the dynamic responses are included in the CAE fatigue life predictions. The dynamic interactions at the pivot joints are simulated by using two identical CAE models, one with lateral translational constraint applied at the left pivot only and the other at the right pivot only.
Journal Article

A Fatigue Life Prediction Method of Laser Assisted Self-Piercing Rivet Joint for Magnesium Alloys

2015-04-14
2015-01-0537
Due to magnesium alloy's poor weldability, other joining techniques such as laser assisted self-piercing rivet (LSPR) are used for joining magnesium alloys. This research investigates the fatigue performance of LSPR for magnesium alloys including AZ31 and AM60. Tensile-shear and coach peel specimens for AZ31 and AM60 were fabricated and tested for understanding joint fatigue performance. A structural stress - life (S-N) method was used to develop the fatigue parameters from load-life test results. In order to validate this approach, test results from multijoint specimens were compared with the predicted fatigue results of these specimens using the structural stress method. The fatigue results predicted using the structural stress method correlate well with the test results.
Technical Paper

Development of a Nonlinear, Hysteretic and Frequency Dependent Bushing Model

2015-04-14
2015-01-0428
An accurate bushing model is vital for vehicle dynamic simulation regarding fatigue life prediction. This paper introduces the Advanced Bushing Model (ABM) that was developed in MATLAB® environment, which gives high precision and fast simulation. The ABM is a time-domain model targeting for vehicle durability simulation. It dynamically captures bushing nonlinearities that occur on stiffness, damping and hysteresis, through a time-history-based fitting technique, compensated with frequency dependency functionality. Among the simulated and test-collected bushing loads, good correlations have been achieved for elastomer bushings and hydraulic engine mounts and validated with a random excitation signal. This ABM model has been integrated into a virtual shaker table (from a parallel project) as the engine mount model to simulate the mount load, and has shown acceptable prediction on fatigue damage.
Technical Paper

Fatigue Life Prediction for Adaptable Insert Welds between Sheet Steel and Cast Magnesium Alloy

2016-04-05
2016-01-0392
Joining technology is a key factor to utilize dissimilar materials in vehicle structures. Adaptable insert weld (AIW) technology is developed to join sheet steel (HSLA350) to cast magnesium alloy (AM60) and is constructed by combining riveting technology and electrical resistance spot welding technology. In this project, the AIW joint technology is applied to construct front shock tower structures composed with HSLA350, AM60, and Al6082 and a method is developed to predict the fatigue life of the AIW joints. Lap-shear and cross-tension specimens were constructed and tested to develop the fatigue parameters (load-life curves) of AIW joint. Two FEA modeling techniques for AIW joints were used to model the specimen geometry. These modeling approaches are area contact method (ACM) and TIE contact method.
Technical Paper

An Experimental Study on Static and Fatigue Strengths of Resistance Spot Welds with Stack-up of Advanced High Strength Steels and Adhesive

2016-04-05
2016-01-0389
This paper describes static and fatigue behavior of resistance spot welds with the stack-up of conventional mild and advanced high strength steels, with and without adhesive, based on a set of lap shear and coach peel coupon tests. The coupons were fabricated following specified spot welding and adhesive schedules. The effects of similar and dissimilar steel grade sheet combinations in the joint configuration have been taken into account. Tensile strength of the steels used for the coupons, both as-received and after baked, and cross-section microstructure photographs are included. The spot weld SN relations between this study and the study by Auto/Steel Partnership are compared and discussed.
Technical Paper

Assessment of Critical Plane Models Using Non-Proportional Low Cycle Fatigue Test Data of 304 Stainless Steel

2016-04-05
2016-01-0380
Two popular critical plane models developed by Fatemi-Socie and Smith-Watson-Topper were derived from the experimental observations of the nucleation and growth of cracks during loading. The Fatemi-Socie critical plane model is applicable for the life prediction of materials for which the dominant failure mechanism is shear crack nucleation and growth, while the Smith-Watson-Topper model, for materials that fail predominantly by crack growth on planes perpendicular to the planes of maximum tensile strain or stress. The two critical plane models have been validated primarily by in-phase and 90° out-of-phase loading, and few, on the complex, non-proportional loading paths. A successful critical plane model should be able to predict both the fatigue life and the dominant failure planes. However, some experimental studies indicate the 304 stainless steel has the two possible failure modes, shear and tensile failure dominant, depending on the loading mode and stress and strain states.
Technical Paper

Fatigue Life Prediction of Friction Stir Linear Welds for Magnesium Alloys

2016-04-05
2016-01-0386
Friction stir linear welding (FSLW) is widely used in joining lightweight materials including aluminum alloys and magnesium alloys. However, fatigue life prediction method for FSLW is not well developed yet for vehicle structure applications. This paper is tried to use two different methods for the prediction of fatigue life of FSLW in vehicle structures. FSLW is represented with 2-D shell elements for the structural stress approach and is represented with TIE contact for the maximum principal stress approach in finite element (FE) models. S-N curves were developed from coupon specimen test results for both the approaches. These S-N curves were used to predict fatigue life of FSLW of a front shock tower structure that was constructed by joining AM60 to AZ31 and AM60 to AM30. The fatigue life prediction results were then correlated with test results of the front shock tower structures.
Technical Paper

Study of Ausferrite Transformation Kinetics for Austempered Ductile Irons with and without Ni

2016-04-05
2016-01-0421
This research studies the transformation kinetics of austempered ductile iron (ADI) with and without nickel as the main alloying element. ADI has improved mechanical properties compared to ductile iron due to its ausferrite microstructure. Not only can austempered ductile iron be produced with high strength, high toughness and high wear resistance, the ductility of ADI can also be increased due to high carbon content austenite. Many factors influence the transformation of phases in ADI. In the present work, the addition of nickel was investigated based on transformation kinetics and metallography observation. The transformation fractions were determined by Rockwell hardness variations of ADI specimens. The calculation of transformation kinetics and activation energy using the “Avrami Equation” and “Arrhenius Equation” is done to describe effects of nickel alloy for phase reactions.
Technical Paper

A New Measurement of Aluminum Alloy Edge Stretching Limit Based on Digital Image Correlation Method

2016-04-05
2016-01-0417
In Aluminum Alloy, AA, sheet metal forming, the through thickness cracking at the edge of cut out is one of the major fracture modes. In order to prevent the edge cracking in production forming process, practical edge stretch limit criteria are needed for virtual forming prediction and early stamping trial evaluations. This paper proposes new methods for determining the edge stretching limit of the sheet coupons, with and without pre-stretching, based on the Digital Image Correlation (DIC) technique. A numbers of sets of notch-shaped smaller coupons with three different pre-stretching conditions (near 5%, 10% and fractured) are cut from the prestretched large specimens. Then the notch-shaped smaller coupons are stretched by uniaxial tension up to through edge cracking observed. A dual-camera 3D-DIC system is utilized to measure both coupon face strain and thickness strain in the notch area at the same time.
Technical Paper

Dimension Study of Punched Hole Using Conical Tipped Punches

2016-04-05
2016-01-0364
Dimensional problems for punched holes on a sheet metal stamping part include being undersized and oversized. Some important relationships among tools and products, such as the effect of conical punch tip angle, are not fully understood. To study this effect, sheets of AA6016 aluminum and BH210 steel were punched by punches with different conical tip angles. The test method and test results are presented. The piercing force and withdrawing force when using conical punches were also studied. The results indicate that the oversize issue for a punched hole in a stamped panel is largely due to the combination of the conical tip effect and the stretching-release effect.
Journal Article

Review and Assessment of Frequency-Based Fatigue Damage Models

2016-04-05
2016-01-0369
Several popular frequency-based fatigue damage models (Wirsching and Light, Ortiz and Chen, Larsen and Lutes, Benascuitti and Tovo, Benascuitti and Tovo with α.75, Dirlik, Zhao and Baker, and Lalanne) are reviewed and assessed. Seventy power spectrum densities with varied amplitude, shape, and irregularity factors from Dirlik’s dissertation are used to study the accuracies of these methods. Recommendations on how to set up the inverse fast Fourier transform to synthesize load data and obtain accurate rainflow cycle counts are given. Since Dirlik’s method is the most commonly used one in industry, a comprehensive investigation of parameter setups for Dirlik’s method is presented. The mean error and standard deviation of the error between the frequency-based model and the rainflow cycle counting method was computed for fatigue slope exponent m ranging from 3 to 12.
Journal Article

Considerations of Vibration Fatigue for Automotive Components

2017-03-28
2017-01-0380
As an automobile is driven, its components and structures consistently experience the random excitations from road inputs and periodic vibration from engine firing. This could cause durability issues if the component structure isn’t fully validated. Vibration fatigue is a field of study regarding the assessment and improvement of a component’s or system’s robustness to vibration inputs. This paper introduces aspects of vibration fatigue to help designers, release engineers, and test engineers better understand the requirements, testing methodologies available, and strategies for improving vibration fatigue performance for the design and validation testing of their products. Vibration characteristics such as typical vibration levels and frequency content for varied areas in the automotive environment are introduced. Methodologies available for conducting actual vibration testing are introduced with listed advantages and disadvantages.
Technical Paper

Aluminum Sheet Springback (Side-Wall-Curl) Study

2017-03-28
2017-01-0396
Vehicle weight reduction is a significant challenge for the modern automotive industry. In recent years, the amount of vehicular components constructed from aluminum alloy has increased due to its light weighting capabilities. Automotive manufacturing processes, predominantly those utilizing various stamping applications, require a thorough understanding of aluminum fracture predictions methods, in order to accurately simulate the process using Finite Element Method (FEM) software or use it in automotive engineering manufacture. This paper presents the strain distribution of A5182 aluminum samples after punch impact under various conditions by Digital Image Correlation (DIC) system, its software also measured the complete strain history, in addition to sample curvature after it was impacted; therefore obtaining the data required to determine the amount of side-wall-curl (Aluminum sheet springback) present after formation.
Technical Paper

Effect of Pre-Strain on Edge Cracking Limit for Advanced High-Strength Steel Using Digital Image Correlation

2017-03-28
2017-01-0394
Advanced high-strength steel (AHSS) is gaining popularity in the automotive industry due to its higher final part strength with the better formability compares to the conventional steel. However, the edge fracture occurs during the forming procedure for the pre-strained part. To avoid the edge fracture that happens during the manufacturing, the effect of pre-strain on edge cracking limit needs to be studied. In this paper, digital image correlation (DIC), as an accurate optical method, is adopted for the strain measurement to determining the edge cracking limit. Sets of the wide coupons are pre-strained to obtain the samples at different pre-strain level. The pre-strain of each sample is precisely measured during this procedure using DIC. After pre-straining, the half dog bone samples are cut from these wide coupons. The edge of the notch in the half dog bone samples is created by the punch with 10% clearance for the distinct edge condition.
Technical Paper

Simultaneous Durability Assessment and Relative Random Analysis Under Base Shake Loading Conditions

2017-03-28
2017-01-0339
For many automotive systems it is required to calculate both the durability performance of the part and to rule out the possibility of collision of individual components during severe base shake vibration conditions. Advanced frequency domain methods now exist to enable the durability assessment to be undertaken fully in the frequency domain and utilizing the most advanced and efficient analysis tools (refs 1, 2, 3, 4, 5). In recent years new capabilities have been developed which allow hyper-sized models with multiple correlated loadcases to be processed. The most advanced stress processing (eg, complex von-Mises) and fatigue algorithms (eg, Strain-Life) are now included. Furthermore, the previously required assumptions that the loading be stationary, Gaussian and random have been somewhat relaxed. For example, mixed loading like sine on random can now be applied.
Technical Paper

Use of Parametric Approach to Optimize Structural Adhesives and Spot Welds in CAE Based Optimization

2017-03-28
2017-01-0254
Use of parametric approach to optimize CAE models for various objectives is a common practice these days. In addition to load members, the connection entities such as welds and adhesives play an important role in overall performance matrix. Hence adding the connection entities to the pool of design variables during an optimization exercise provide additional opportunity for design exploration. The method presented in this paper offers a unique approach to parameterize adhesive lines by evaluating the possibility of using structural adhesives as intermittent patches rather than continuous lines. The paper discusses two optimization studies 1) structural adhesive patches along with spot weld pitch as design variables, and 2) structural adhesive patches with gage variables. These studies include the Body in White (BiW) and Trimmed Body in White (TBiW) assessments.
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