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Technical Paper

Warpage Prediction on Injection Molded Semi-Crystalline Thermoplastics

Warpage is the distortion induced by inhomogeneous shrinkage during injection molding of plastic parts. Uncontrolled warpage will result in dimensional instability and bring a lot of challenges to the mold design and part assembly. Current commercial simulation software for injection molding cannot provide consistently accurate warpage prediction, especially for semi-crystalline thermoplastics. In this study, the root cause of inconsistency in warpage prediction has been investigated by using injection molded polypropylene plaques with a wide range of process conditions. The warpage of injection molded plaques are measured and compared to the numerical predictions from Moldex3D. The study shows that with considering cooling rate effect on crystallization kinetics and using of the improved material model for residual stress calculations, good agreements are obtained between experiment and simulation results.
Journal Article

Modeling Forming Limit in Low Stress Triaxiality and Predicting Stretching Failure in Draw Simulation by an Improved Ductile Failure Criterion

A ductile failure criterion (DFC), which defines the stretching failure at localized necking (LN) and treats the critical damage as a function of strain path and initial sheet thickness, was proposed in a previous study. In this study, the DFC is revisited to extend the model to the low stress triaxiality domain and demonstrates on modeling forming limit curve (FLC) of TRIP 690. Then, the model is used to predict stretching failure in a finite element method (FEM) simulation on a TRIP 690 steel rectangular cup draw process at room temperature. Comparison shows that the results from this criterion match quite well with experimental observations.
Technical Paper

Predicting Forming Limit Curve Using a New Ductile Failure Criterion

Based on findings from micromechanical studies, a Ductile Failure Criterion (DFC) was proposed. The proposed DFC treats localized necking as failure and critical damage as a function of strain path and initial sheet thickness. Under linear strain path assumption, a method to predict Forming Limit Curve (FLC) is derived from this DFC. With the help of predetermined effect functions, the method only needs a calibration at uniaxial tension. The approach was validated by predicting FLCs for sixteen different aluminum and steel sheet metal materials. Comparison shows that the prediction matches quite well with experimental observations in most cases.
Technical Paper

A Transportable Instrumentation Package for In-Vehicle On-Road Data Collection for Driver Research

We present research in progress to develop and implement a transportable instrumentation package (TIP) to collect driver data in a vehicle. The overall objective of the project is to investigate the symbiotic relationship between humans and their vehicles. We first describe the state-of-art technologies to build the components of TIP that meet the criteria of ease of installation, minimal interference with driving, and sufficient signals to monitor driver state and condition. This method is a viable alternative to current practice which is to first develop a fully instrumented test vehicle, often at great expense, and use it to collect data from each participant as he/she drives a prescribed route. Another practice, as for example currently being used in the SHRP-2 naturalistic driving study, is to install the appropriate instrumentation for data collection in each individual's vehicle, often requiring several hours.
Technical Paper

Seat Comfort as a Function of Occupant Characteristics and Pressure Measurements at the Occupant-Seat Interface

Seat comfort is a highly subjective attribute and depends on a wide range of factors, but the successful prediction of seat comfort from a group of relevant variables can hold the promise of eliminating the need for time-consuming subjective evaluations during the early stages of seat cushion selection and development. This research presents the subjective seat comfort data of a group of 30 participants using a controlled range of seat foam samples, and attempts to correlate this attribute with a) the anthropometric and demographic characteristics of the participants, b) the objective pressure distribution at the body-seat interface and c) properties of the various foam samples that were used for the test.
Technical Paper

How the University of Michigan-Dearborn Prepares Engineering Graduates for Careers in Automotive Systems Engineering

The automotive industry is expected to accelerate the transition to revolutionary products, rapid changes in technology and increasing technological sophistication. This will require engineers to advance their knowledge, connect and integrate different areas of knowledge and be skilled in synthesis. In addition, they must learn to work in cross-disciplinary teams and adopt a systems approach. The College of Engineering and Computer Science (CECS) at the University of Michigan-Dearborn (UM-Dearborn) responded by creating interdisciplinary MS and Ph.D. programs in automotive systems engineering (ASE) and augmenting them with hands-on research. Students at the undergraduate level can also engage in numerous ASE activities. UM-Dearborn's ASE programs offer interesting and possibly unique advantages. The first is that it offers a spectrum of ASE degree and credit programs, from the MS to the Ph.D. to continuing education.
Technical Paper

Simulating an Integrated Business Environment that Supports Systems Integration

This paper describes the design and application of a business simulation to help train employees about the new business model and culture that for an automotive supplier company that designs connected vehicle and other advanced electronic products for the automotive industry. The simulation, called SIM-i-TRI, is a three to four day collaborative learning activity that simulates the executive, administrative, engineering, manufacturing, and marketing functions in three divisions of a manufacturer that supplies parts and systems to customers in industries similar to the automotive industry. It was originally designed to support the new employee orientation at the Tier 1 supplier and to provide the participants a safe environment to practice the lessons from the orientation. The simulation has been used several times a month in the US, England, and Germany for over four years.
Technical Paper

Prestrain Effect on Fatigue of DP600 Sheet Steel

The component being formed experiences some type of prestrain that may have an effect on its fatigue strength. This study investigated the forming effects on material fatigue strength of dual phase sheet steel (DP600) subjected to various uniaxial prestrains. In the as-received condition, DP600 specimens were tested for tensile properties to determine the prestraining level based on the uniform elongation corresponding to the maximum strength of DP600 on the stress-strain curve. Three different levels of prestrain at 90%, 70% and 50% of the uniform elongation were applied to uniaxial prestrain specimens for tensile tests and fatigue tests. Fatigue tests were conducted with strain controlled to obtain fatigue properties and compare them with the as-received DP600. The fatigue test results were presented with strain amplitude and Neuber's factor.
Technical Paper

A Value Analysis Tool for Automotive Interior Door Trim Panel Materials and Process Selection

This paper describes a computerized value analysis tool (VAT) developed to aid automotive interior designers, engineers and planners to achieve the high levels of perceived quality of materials used in automotive door trim panels. The model requires a number of inputs related to types of materials, their manufacturing processes and customer perceived quality ratings, costs and importance of materials, features located in different areas of the door trim panel, etc. It allows the user to conduct iterative evaluation of total cost, total weighted customer perceived quality ratings, and estimates of perceived value (perceived quality divided by cost) for different door trim areas as well as the entire door trim panel. The VAT, thus, allows value and cost management related to materials and processing choices for automotive interiors.
Technical Paper

Formability Analysis of Thermoplastic Lightweight Fiber-Metal Laminates

This study investigates numerically and experimentally the formability of two Fiber-Metal Laminate systems based on a thermoplastic self-reinforced polypropylene and a glass fiber polypropylene composite materials. These hybrid systems consist of layered arrangements of aluminum 2024-T3 sheets and thermoplastic-based composite materials. Flat panels were manufactured using a fast one step cold press manufacturing procedure. Punch-stretch forming tests and numerical simulations were performed in order to evaluate the formability of the hybrid systems. Experimental and simulation results revealed that the self reinforced thermoplastic composite-based Fiber-Metal Laminate exhibit excellent forming properties similar to that of the monolithic aluminum alloy of comparable thickness.
Technical Paper

Interfacial Fracture in Environmentally Friendly Thermoplastic Composite-Metal Laminates

This paper investigates the interfacial fracture properties of composite-metal laminates by using the single-cantilever beam testing technique. The hybrid systems consisted of a layer of aluminum alloy (6061 or 2024-T3) bonded to polypropylene based composites. In this study, two non-chromate surface treatments were applied to the aluminum substrates: SafeGard CC-300 Chrome free seal (from Sanchem Inc.) and TCP-HF (from Metalast International Inc.). These are environmentally friendly surface treatments that enhance the adhesion and corrosion resistance of aluminum alloys. Flat hybrid panels were manufactured using a one step cold press manufacturing procedure. Single cantilever bend specimens were cut from the panels and tested at 1mm/min. Results have shown that the CC-300 treated Al 2024-T3 alloy and Twintex exhibited higher interfacial fracture energy values.
Technical Paper

Formability of Ti-TWBs at Elevated Temperatures

In this paper, the formability of Ti-TWBs at different elevated temperatures is experimentally investigated. Ti-TWBs made of Ti-6Al-4V sheets with thicknesses of 0.7mm and 1.0mm are manufactured. Then, the tensile test and forming test at elevated temperatures, ranging from room temperature to 600°C, have been carried out to determine the mechanical properties and the formability of the prepared Ti-TWBs respectively. The effects of elevated temperatures on both the forming and failure behaviors of the Ti-TWBs are examined by comparing with that of the Ti-6Al-4V base metal. It is found that the formability of the Ti-TWBs at room temperature with a dissimilar thickness combination is lower than that of their base metal, whilst the formability of both the Ti-TWBs and their base metal increases with increasing forming temperature. In addition, failures have often been found at the thinner base metal during the Ti-TWB forming, provided that the quality weld is attained without defect.
Technical Paper

Towards Development of a Methodology to Measure Perception of Quality of Interior Materials

The automotive interior suppliers are challenged to develop materials, that not only perform functionally, but also provide the right combination sensory experience (e.g. visual appeal, tactile feeling) and brand differentiation at very competitive costs. Therefore, the objective of this research presented in this paper is to develop a methodology that can be used to measure customer perception of interior materials and to come up with a unique system for assessing value of different interior materials. The overall methodology involves the application of a number of psychophysical measurement methods (e.g. Semantic Differential Scaling) and statistical methods to assess: 1) overall customer perceived quality of materials, 2) elements (or attributes) of perception, and 3) value of materials from OEM's viewpoint in terms of the measurement of perception of quality divided by a measure of cost.
Technical Paper

Independent Control of All-Wheel-Drive Torque Distribution

The sophistication of all-wheel-drive technology is approaching the point where the drive torque to each wheel can be independently controlled. This potentially offers vehicle handling enhancements similar to those provided by Dynamic Stability Control, but without the inevitable reduction in vehicle acceleration. Independent control of all-wheel-drive torque distribution would therefore be especially beneficial under acceleration close to the limit of stability. A vehicle model of a typical sports sedan was developed in Simulink, with fully independent control of torque distribution. Box-Behnken experimental design was employed to determine which torque distribution parameters have the greatest impact on the vehicle course and acceleration. A proportional-integral control strategy was implemented, applying yaw rate feedback to vary the front-rear torque distribution, and lateral acceleration feedback to adjust the left-right distribution.
Technical Paper

Cost-Benefit Analysis of Thermoplastic Matrix Composites for Structural Automotive Applications

This paper presents cost-benefit analysis of glass and carbon fiber reinforced thermoplastic matrix composites for structural automotive applications based on press forming operation. Press forming is very similar to stamping operation for steel. The structural automotive applications involve beam type components. The part selected for a case study analysis is a crossbeam support for instrument panels.
Technical Paper

LS-DYNA3D Simulation of Sheet Metal Forming using Damage Based User Subroutine

LS-DYNA3D has been widely used to perform computer simulation of sheet metal forming. In the material library of LS-DYNA3D there are a number of user defined material models. In order to take full advantage of the material subroutines, it is important for the users to be able to display user defined history variables in the post processing and to establish user-defined failure criterion. In this report, the development of a damage coupled plastic model is firstly described. The damage model is then programmed in a user defined material subroutine. This is followed by performing finite element simulation of sheet metal forming with the LS-DYNA3D that has incorporated the damage coupled plastic model. The way to display the user defined history variables and how to deal with the failure criterion during the postprocessing of ETA/DYNAFORM are described. History variable distributions at several time steps are displayed and discussed in this paper.
Technical Paper

Formability of Aluminum Tailor-Welded Blanks

The use of tailor welded blanks (TWBs) in automotive applications is increasing due to the potential of weight and cost savings. These blanks are manufactured by joining two or more sheets of dissimilar gauge, properties, or both, to form a lighter blank of desired strength and stiffness. This allows an engineer to “tailor” the properties of the blank to meet the design requirements of a particular panel. TWBs are used in such places as door inner panels, lift gates, and floor pans. Earlier investigations of the use of TWBs targeted steel alloys, but the potential of further weight savings with aluminum TWBs is gaining interest in the automotive industry. Unlike steel TWBs, the welds in aluminum TWBs are not significantly stronger than the base material and are occasionally the fracture site. Additionally, the reduced formability of aluminum, as compared with drawing-quality steels, makes the application of aluminum TWBs more difficult than steel TWBs.
Technical Paper

Prediction of Limit Strains in Sheet Metal Forming Under Complex Strain History

In this paper, a predictive method is developed to determine the forming limit strain and fracture limit strain in a stamped automotive component subjected to a complex strain history that would be experienced during an actual forming operation. The method of analysis is based on a damage mechanics model developed recently by the authors and extended to take into account the hysteretic effects of the principal strain and damage planes. The forming limit and fracture limit strains are then predicted using the modified damage model. Satisfactory predictions have been achieved for a practical case where the complex strain history is prescribed based an actual stamping operation.
Technical Paper

Prediction and Experimental Validation of Path-Dependent Forming Limit Diagrams of VDIF Steel

Strains in most stamped parts are produced under non-proportional loading. Limit strains induced during forming are, therefore, path dependent. Experimental Forming Limit Diagrams (FLDs) are usually determined under proportional loading and are not applicable to most forming operations. Experimental results have shown that path dependent FLDs are different from those determined under proportional loading. A number of analytical methods have been used to predict FLDs under proportional loading. The authors have recently introduced a new method for predicting FLDs based on the theory of damage mechanics. The damage model was used successfully to predict proportional FLDs for VDIF steel and Al6111-T4. In this paper, the anisotropic damage model was used to predict non-proportional FLDs for VDIF steel. Experiments were conducted to validate model predictions by applying pre-stretch in plane strain followed by uniaxial and balanced biaxial tension.
Technical Paper

Prediction of Forming Limit Diagram with Damage Analysis

Based on the theory of damage mechanics, an orthotropic damage model for the prediction of forming limit diagram (FLD) is developed. The conventional method of FLD used to predict localized necking adopts two fundamentally different approaches. Under biaxial loading, the Hill's plasticity method is often chosen when α (= ε2/ε1) < 0. On the other hand, the M-K method is adopted for the prediction of localized necking when α > 0 or the biaxial stretching of sheet metal is pronounced. The M-K method however suffers from the arbitrary selection of the imperfection size, thus resulting in inconsistent predictions. The orthotropic damage model developed for predicting the FLD is based on the anisotropic damage model recently proposed by Chow et al (1993). The model is extended to take into account, during the sheet forming process, orthotropic plasticity and damage. The orthotropic FLD model consists of the constitutive equations of elasticity and plasticity coupled with damage.