Investigation of weight reduction of automotive body structures with the use of sandwich materials

The use of sandwich materials in automobile body panels is investigated in this study. In the first part, floor, luggage, firewall and rear wheel panels of a car body-in-white are replaced with panels made of sandwich materials in order to reduce the weight. Final sandwich material configurations are obtained through a trial and error based optimization approach where weights of the panels are minimized while keeping bending stiffness performances of the panels same. In the second part, the use of sandwich materials in laminated steel form as light weight alternatives to free layer surface damping treatments attached to floor panels is investigated. Free layer damping treatments are applied to body panels to decrease primarily the structure-borne noise inside the cabin. This effect is achieved by increasing structural damping in the panel structures. It has been demonstrated that, same level of vibration damping increase in a floor panel can be achieved using a sandwich material in laminated steel form with a lesser amount of weight addition to the original sheet metal floor panel compared to a free layer surface damping treatment. (C) 2016 The Authors. Published by Elsevier B.V

Araç sürüş konforunun artırılması için pasif titreşim sönümleyicilerinin geliştirilmesi ve test edilmesi

TÜBİTAK MAG15.10.2013Bu çalışmada, doğrusal ve dönel ayarlanabilir titreşim emicilerinin (ATE) ve kaldıraç tipli titreşim izolatörler (KTİ) araç sürüş konforuna etkileri çeyrek araba modeli üzerinde incelenmiştir. ATE'ler, özellikle kendi doğal frekanslarında, sistemin enerjisini kendi üzerine alarak titreşimleri azaltmaktadırlar. Doğrusal ATE'lerin süspansiyon sistemlerine uygulanması kolay olmasına rağmen döner ATE'ler atalet etkilerinin daha fazla olması sebebiyle daha iyi performans göstermektedirler. Elde edilen sonuçlar ATE'lerin tekerlek sıçrama frekansı civarındaki dar bir frekans aralığında sürüş konforunu arttırdığını göstermektedir. ATE’lere ek olarak değişik kütlelere sahip çeşitli KTİ konfigürasyonları incelenmiş ve KTİ'lerin hem araç sıçrama hem de tekerlek sıçrama frekanslarında titreşim genliklerini önemli oranda azalttığı görülmüştür. Ancak bu çalışma sırasında ATE ve KTİ’leri kullanabilmek için önerilen parçalı süspansiyon sistemi araç sürüş konforunu çok önemli bir oranda arttırmıştır. Parçalı süspansiyon sisteminin sürüş konforuna olan olumlu etkilerinin yanında ATE’ler neredeyse etkisiz kalmıştır. KTİ’ler ise parçalı süspansiyon sisteminin gerçekleştirdiği iyileştirmeyi belli frekans bölgelerinde biraz daha arttırdığı gözlemlenmiştir. Dolayısıyla ayarlanmış parçalı süspansiyon sistemi araç sürüş konforunun arttırılması konusunda çok önemli alternatif olarak karşımıza çıkmıştır. Teorik olarak gerçekleştirilen bu çalışmalarının gerçek durumdaki etkilerini gözlemleyebilmek için proje çalışması kapsamında ölçeklendirilmiş bir çeyrek araç test düzeneği tasarlanmıştır. Tasarlanan bu test düzeneği üzerinde teorik çalışmalar neticesinde araç sürüş konforunu arttırdığı belirlenen konfigürasyonlar test edilmiş ve testler sonucunda sürüş konforunda teorik modeller ile elde edilen sonuçlara benzer iyileşmelerin elde edildiği gözlemlenmiştir.In this study, the effects of utilization linear and rotational tuned vibration absorbers (TVA) and lever type vibration isolators (LVI) on vehicle ride comfort are investigated a quarter car model. TVAs decrease the vibrations of the system they are mounted on by absorbing energy of the system especially vibrating frequency equal to the natural frequency of TVA. Even though application of linear TVAs on vehicle suspension is easier, rotational TVAs have better performance due to their increased inertia effect. The results obtained show that TVAs improve ride comfort only at a narrow frequency band around the wheel hop frequency. In addition to TVAs, LVIs with different masses and configurations are as well studied and it is observed that LVIs decrease vibration amplitudes both at the wheel hop and body bounce frequencies. On the other hand, it discovered that the divided suspension system proposed in this study in order to use TVAs and LVIs improved ride comfort significantly, even though TVAs and LVIs are not present. As a result of this significant improvement in ride comfort, the effect of TVAs is observed to be negligible. However, addition of LVIs onto the divided suspension system increase the improvement in ride comfort at certain frequencies, slightly. Therefore, divided suspension system turns out to be an important alternative in increasing vehicle ride comfort. In order to observe the effects these theoretical models, a scaled quarter car experimental setup is as well designed. Theoretical configurations that result in improvement in vehicle ride comfort is tested utilizing this experimental setup where similar improvements as in the case of mathematical models are observed

Design and development of a complex shear modulus measurement setup for viscoelastic materials

Details of the design and development study of a complex shear modulus measurement setup for viscoelastic materials have been presented in this paper. The new setup is specifically designed for measuring the complex shear modulus of pressure sensitive adhesives. The setup consists of a rigid block that is connected to a rigid fixture through two identical shear specimens of the viscoelastic material to be tested. The rigid block and the shear specimens resemble a single degree of freedom system. Once the frequency response function of the rigid block is measured, the frequency dependent material properties of the viscoelastic material can be calculated in a frequency range of 20 to 200 Hz. The setup also has a forced liquid convection heating/cooling system that enables testing in a temperature range of 5° F to 200° F. Test results for a sample viscoelastic material have also been presented in this paper. Basic principals of this testing method can be found in various sources, yet very few of them provide detailed information for practical implementation. Also, unlike the widely-known vibrating beam technique, no detailed standards exist on the subject. The main objective of this paper is to be an aid for future implementations of the testing approach through summarizing this recent effort for the design, analysis and construction of a sample test setup

Applications of the dynamic stiffness matrix (DSM) based direct damping identification method

Two potential applications of a dynamic stiffness matrix (DSM) based direct damping matrix identification method are presented in this paper. The method was proposed to identify both the mechanism and spatial distribution of damping as a matrix of general function of frequency. First potential application is the analytical-experimental hybrid structural dynamics modeling, in which the model is constructed by combining analytically formulated mass and stiffness matrices with the experimentally identified damping matrix. Second application is the direct measurement of complex shear modulus of viscoleastic materials. The real and imaginary parts of the dynamic stiffness measured on a test setup that resembles a single degree of freedom system is used to compute the shear modulus and the loss factor of viscoelastic materials

Further developments in the dynamic stiffness matrix (DSM) based direct damping identification method

Theoretical development of a dynamic stiffness matrix (DSM) based direct damping matrix identification method is revisited in this paper. This method was proposed to identify both the mechanism and spatial distribution of damping in dynamic structures as a matrix of general function of frequency. The objective of this paper, in addition to the review of the theoretical development, is to investigate some major issues regarding the feasibility of this method. The first issue investigated is how the errors in measured frequency response functions (FRF) affect the accuracy of the DSM. It was already known that the DSM is highly sensitive to errors that are present in the FRF. A detailed analytical and computational study is conducted, which finally leads to a sound physical explanation of the high sensitivity of the DSM to measurement errors. A new and also important conclusion is that the leakage error drastically affects the accuracy of the computed DSM. The second major issue reported is the experimental implementation of the DSM based method to minimize the leakage error. Based on the findings presented in this study, a new and improved test setup is designed and developed, which enables the authors to obtain a good quality result that supports the theoretical and numerical analyses previously conducted

Error analysis and feasibility study of dynamic stiffness matrix-based damping matrix identification

Developing a method to formulate a damping matrix that represents the actual spatial distribution and mechanism of damping of the dynamic system has been an elusive goal. The dynamic stiffness matrix (DSM)-based damping identification method proposed by Lee and Kim is attractive and promising because it identifies the damping matrix from the measured DSM without relying on any unfounded assumptions. However, in ensuing works it was found that damping matrices identified from the method had unexpected forms and showed traces of large variance errors. The causes and possible remedies of the problem Lire sought for in this work. The variance and leakage errors are identified as the major sources of the problem, which Lire then related to system parameters through numerical and experimental simulations. An improved experimental procedure is developed to reduce the effect of these errors in order to make the DSM-based damping identification method a practical option

Direct identification and expansion of damping matrix for experimental-analytical hybrid modeling

The theory of direct experimental identification of damping matrix based on the dynamic stiffness matrix (DSM) method is further developed in this work. Based on the relationship between the DSMs of the smaller experimental model and larger analytical model, the mathematical relationship between the damping matrices of the two models is established. Examining the relationship, two methods are developed that can be used to expand the experimental damping matrix to the size of the analytical model. Validity of the expansion methods is demonstrated with numerical examples. The expanded damping matrix is intended to be combined with analytically formulated stiffness and mass matrices to build an experimental–analytical hybrid model. To find the frequency range, in which such a hybrid modeling is valid, a simple but effective method is developed