Mohd Azmi Yunus

Universiti Teknologi MARA | UiTM · School of Mechanical Engineering

Recently, laser stitch welds are prefered in automotive structure comparing with others joining methods when joining two or more substructures due to its capabilities producing high strength joint with low heat application. However, the vibration responses such as dynamic behaviour of laser stitch welded structure are complex and there is a variety...

Reducing structural weight while increasing modal frequencies is very challenging in structural dynamics. Honeycomb sandwich panels are widely used as alternative structural components to achieve the goal in engineering assembled structures. This research investigates the modal parameters of an aluminium honeycomb sandwich panel with an aluminium s...

Assumptions and simplifications in finite element (FE) modelling for structural vibration analysis contribute to discrepancies in numerical results. This paper presents FE model updating on components of a simplified model of an aircraft pylon. The components are tested under free-free boundary conditions. Impact testing is performed with roving ac...

Analytical modelling of composite structures is found to be difficult to develop especially to predict the structural vibration responses due to the complicated of components itself such as matrix-reinforcement element, fibre orientation and unknown properties fibre raw material during fabrication stages of composite structures. The uncertainties o...

The laser spot weld is widely used to join automotive structural components due to the advantages of being inexpensive and more efficient. However, developing a reliable FE model of a laser spot weld for investigating a structure's modal parameters is very challenging. A repeated assessment of the welded joint model can significantly affect the eff...

Tungsten inert gas (TIG) welding is an electrical arc welding method that commonly used in the fabrication of engineering structure to join either ferrous or nonferrous metals due to great control over weld area comparing to other welding methods such as metal inert gas (MIG). A limited study can be found on finite element (FE) modelling technique...

The modal parameters of a laser spot welded hat plate are investigated using finite element analysis(FEA) and experimental modal analysis (EMA). A new scheme of FE modelling residual stress effects is proposed and evaluated. The modal parameters were characterised using impact testing and roving accelerometers under a free configuration. Normal mod...

Bolted joint structure is one of the complex types of the assembled structure that is applied in different sectors of industries. The benefit of the joining method using bolt and nut including low production cost, low maintenance and simplistic design of assembly. The prediction of dynamic behaviour of the bolted joins assembled structure is very c...

Stochastic model updating based on perturbation theory has been widely applied to quantify uncertain parameters in structural systems due to its simplicity and straightforward approach. Nevertheless, the significant requirements for establishing a good correlation in the initial prediction of structural responses and small perturbations in uncertai...

For frequency-based substructuring (FBS) to be accurate, translational and rotational data must be available at the connection points between substructures. However, obtaining rotational FRFs from experimental modal analyses is very difficult in practice. In this paper, an alternative method for estimating rotational FRFs is proposed using an appro...

Modelling the dynamic characteristics of the bolted joints in a complex assembled structure with a high accuracy is very challenging due to the assumptions and uncertainties in the input data of the FE model. In this paper, the identification of the dynamic characteristics of the bolted joints structure using the CBUSH element connector is proposed...

Efficient schemes to represent mathematical model of thin-sheet metal structures jointed by bolted joints for accurately predict the structure dynamic behaviour has been a significant unresolved issue in structural dynamics community. The biggest challenge is to efficiently incorporate the joints local deformation effects on the developed mathemati...

Structural stiffness exerts from joint connections and contact interfaces are significantly affect the dynamic behaviour of the bolt-jointed structure. Randomness in the joint connections due to the manufacturing variability in the identical bolted joints and uncertainty in contact interfaces due to the assambled and reassambled of the joint struct...

The rotational frequency response function (RFRF) plays a crucial role in increasing the accuracy of the calculated results of the frequency-based substructuring method. However, RFRFs are often omitted due to the difficulties in the measurement process and limitations of the equipment. This paper presents a scheme of estimating the rotational FRF...

Structural design and analysis require accurate and precise finite element model in order to have a structure with high safety conditions such as aerospace, offshore and civil structures. However, the predicted results of the finite element model are often considerably different from the experimental results due to the modelling assumptions and sim...

The aim of this paper is to perform experimental modal analysis of two-storey reinforced concrete frame which designed using BS 8110 without seismic load and validate the experimental result with model using finite element analysis software. Experimental Modal Analysis (EMA) is the process of determining the modal parameters such as natural frequen...

The identification of the effectdue to structural changes using modal data is very challenging in the structural dynamic modifications (SDM) study. In this paper, the aim of this studyis to identifythe effect of physical changes of a structural system based on the natural frequencies and mode shapes. A mild steel thin plate structure was used in th...

Bolted joints in assembled structures contribute to the dynamic behaviour of the structures but also increase uncertainties in modelling and prediction of the dynamic behaviour. This paper presents a modelling scheme able to reduce uncertainties and increase the accuracy of the prediction. A finite element (FE) model of a bolted joint structure was...

The dynamic behaviour prediction scheme of carbon fibre composite structures are extremely challenging to be performed due to the geometrical ply-by-ply properties and the ply orientation issues. In this paper, a laminated carbon fibre reinforced epoxy plate with elastic and linear layers was used with aim to investigate the dynamic behaviour of th...

Kistler Kshear 8840 piezoelectric rotational accelerometer is designed with an M5 bolt type of mounting and a 5mm diameter of through or pre-tapped hole is required in a structure under test. However, the mounting is not applicable for some cases, and other types of mounting need to be used. This work investigates the applicability and accuracy of...

Efficient and accurate finite element (FE) modelling of bolted joints is essential for increasing confidence in the investigation of structural vibrations. However, modelling of bolted joints for the investigation is often found to be very challenging. This paper proposes an appropriate FE representation of bolted joints for the prediction of the d...

Model updating methods can be adopted to improve the correlation level between the finite element model of a spot welded structure and its test model. However, in the presence of contact interfaces in the vicinity of the welded areas, improving the correlation level is problematic and challenging. An approach for correlating the finite element mode...

The sensitivity based finite element model updating is a common method to improve the correlation between the initial finite element model and actual structure. The method is considered to be deterministic to correct the modelling parameters that lead to better predictions of the dynamic behaviour of a structure. However, for a complex jointed stru...

Predicted results of a finite element model used to develop physical test structures are often found to be not in good agreement with the experimental results due to the invalid assumptions made in finite element modelling. This study will focus on improving the correlation level between the finite element model and experimental model of a car trun...

Structural dynamics in structural engineering analysis involves the modal parameters (natural frequency, mode shape and damping ratio). The modal parameters of engineering structures is mainly influenced by the damping and stiffness properties. This research paper presents the reliability of CELAS element in the finite element modelling to represen...

Nonlinearity is a frequent occurrence in engineering structures. The nonlinearity detection in the operating mechanical systems is important because the nonlinearity can change the dynamic behaviour. The aim of this work is to experimentally measure the nonlinearity of a flexible beam structure due to the different applied dynamic load configuratio...

Structural dynamics in structural engineering analysis involves the modal parameters (natural frequency, mode shape and damping ratio). The modal parameters of engineering structures is mainly influenced by the damping and stiffness properties. This research paper presents the reliability of CELAS element in the finite element modelling to represen...

Estimating rotational frequency response functions (FRFs) from experimental data is very challenging, and the estimation often leads to poor FRFs due to the presence of spurious resonance peaks. In practice, special equipment is essentially required in the measurement process, unless the rotational FRFs are synthesised using measured modal data. Th...

Finite element (FE) model of a structure is highly depended on idealising and simplification of model, however, the model may not truly represent the physical structure. The application of FE model updating is advocated to modify FE model of structure in order to acquired better correlation between the predicted and measured structure response. Nev...

Laser stitch welding is one of the most reliable and efficient permanent metal joining processes in the automotive industry, particularly in the manufacturing of a car body-in-white (BIW). It is widely known that this welding process induces the generation of residual stresses that can influence the dynamic behaviours of welded structures. In order...

Efficient and accurate analytical representation of bolted joints in an assembled structure for the prediction of the dynamic behaviour of the structure has been a crucial unsolved issue in the finite element (FE) community. 3D modelling of bolted joints, possessing a large number of degrees of freedom, leads to very high computational time. This p...

Engineering structures operate with a nonlinear dynamics behaviour at certain amplitude of input range which will produce noticeable changes and unpredictable effects. In this paper, the nonlinear property of a spring is investigated. The simplified mass-spring system is developed which consists of two springs attached on a thin plate structure. Th...

Nowadays, the applications of rivet joints are dramatically increasing because of its capability and efficiency to assemble the engineering structure such as aerospace and mechanical structures. However, every joint such as riveted joint has a significant effect to the overall dynamic behaviour of the assembled structure. This is because, the overa...

Bolted joints, which give easy-to-install and uninstall, have been widely used in various types of mechanical structural assembly and contribute significantly to minimise the magnitudes of resonant peaks of assembled structures. However, modelling of an individual bolted joint within a large assembled structure has always been problematic, especial...

Measuring the dynamic behaviour of a structure made from light thin steel sheets becomes arduous as a result of the double impact, local modes and mass loading issues which lead to inaccurate results. In addition, the attachments of accelerometers, selection of suspension types and methods of excitation adopted to the measurement greatly affect the...

The frequency based substructuring (FBS) method allows the combination between the experimental and analytical frequency response function (FRF). The combined FRF is then used for calculation of the dynamic behaviour of an assembled structure which usually consists of a large number structural components or substructures. However, the accuracy of t...

This paper presents the application of response surface method in finite element model updating, as an approach for improving the accuracy and efficiency of the finite element model of a laser spot welded structure, to reflect the physical responses of the structure. The procedures of implementation for response surface in model updating such as sa...

Analytical modelling of the dynamic behaviour of a laser spot welded structure can be developed using two element connectors which are CWELD and ACM2. In the presence of initial stress in the structure, the performance of these two connectors can be different. In order to properly investigate the dynamic behaviour of the structure, the difference o...

Identifying the appropriate frequency response function (FRF) driving point of complex structures is crucial to experimental modal analysis (EMA), but it is often found to be challenging and problematic. Traditionally, EMA analysts tend to place a reference sensor at several potential driving points and excite the points during testing. However, th...

Laser stitch welding is a joining technique that has been increasingly popular in automotive industries, such as in the manufacturing and assembling of the car’s body-in-white (BiW) due to its advantages over the resistance spot weld, such as low heat application and high strength weld. The dynamic behaviour of a laser stitch welded structure is re...

The accuracy of the predicted dynamic behaviour of an assembled structure using the frequency based substructuring (FBS) method is often found to be diverged from the experimental counterparts. The divergence which has become the paramount concern and major issue for structural dynamicists is because of the unreliable experimental FRF data of the i...

This paper presents the finite element modelling and analysis of the dynamic behaviour of a laser spot welded structure under the influence of initial stress. Modal based updating with a new scheme was used to improve the finite element model of the structure. Element connectors with CWELD ELPAT format were used to represent the laser spot welded i...

Combining analytical with experimental data to predict the dynamic behaviour of an assembled structure via the frequency based substructuring (FBS) method, is a common practice in the field of structural dynamics. However, the accuracy of the dynamic behaviour predicted from the FBS method relies heavily on the quality of experimental frequency res...

Accurate representation of the joint stiffness of bolted joints in the finite element (FE) model of a jointed structure is vital to ensure the accuracy and reliability of the predicted dynamic behaviour of the structure. The aim of this work was to put forward an efficient FE modelling method embodying the representation of the joint stiffness for...

The applications of laser stitch welding are increasing used in assemblies engineering products such as automotive structures due to its efficiency and re-liability in connecting a light weight material. In order to understand the vibration effect of the laser stitch weld towards the assembled structure, it is important to analyse its dynamic behav...

The model validation process known as the finite element model updating method aims to improve the accuracy of the predicted results by reducing the discrepancies between the initial finite element model and the experimental data. The objective of this paper is to investigate the effects of the suspension spring stiffness to the experimental data....

Accurate analytical models of engineering structures are of paramount importance for dynamicists to be used in predicting the dynamic behaviour (frequency response function) of the structures. The finite element method (FEM) and the experimental modal analysis (EMA) have been known as powerful and useful methods that can be used to determine the fr...

Adopting dynamic substructuring schemes is a common practice in the field of structural dynamics, where the dynamic behaviour of a structure is predicted by combining the multiple subsystems that are analysed individually. This paper investigated the dynamic behaviour of a structure with doubled bolted joints using the frequency based substructurin...

Bolted joint commonly being used as a mechanical joint to connect two or more mechanical components which bring an interest to this study. The complexity of joint element plays an important role in the dynamic investigation. Structural damage happens and often it's too late to react to it and early detection of structure failure (damage) is benefic...

Structural dynamic modification (SDM) techniques are important in structural optimisation of the system to modify the dynamics behaviour of the structure. It can be implemented by utilising the dynamic test data to alters the dynamic behaviour of the structure. However, there are some concern in the design process in which the undesirable mode shap...

Acquiring efficient, economic and accurate methods for identifying the material properties of heterogeneous materials have been one of themajor objectives in the mechanical engineering community, thus, inverse methods may be considered as contributing to a very promising way of achieving the objective. This paper is concerned with an inverse method...

This paper presents an investigation of the effect of boundary conditions in experimental modal analysis to approximate the free-free boundary conditions in the experimental modal analysis of a slender beam. Experimental modal analysis and numerical simulation of normal mode analysis were performed to obtain the modal parameters and predicted resul...

Accurate representation of bolted joints in the finite element (FE) model of a built-up structure is a crucial factor in ensuring the accuracy and reliability of the dynamic behaviour prediction of the structure. Modelling of bolted joints in industrial structures has not been widely and thoroughly studied, especially in the dynamic response of the...

The accuracy of the predicted dynamic behaviour of a structure is highly dependent on the accurate properties used in the analytical model. The predicted results computed from the finite element method used to develop the model are often found not to be in good agreement with the experimental results due to the erroneous assumptions made in the fin...

Adopting dynamic substructuring methods to predict the dynamic behaviour of a combined structure is a common practice in the field of structural dynamics. This method has the capability and versatility to combine different sources of data; experimental and analytical, via the frequency based substructuring (FBS) method. This paper investigates the...

A comparative study of the vibrational effects on the boundary conditions of a slender beam Abstract. Accurate representation of bolted joints in the finite element (FE) model of a built-up structure is a crucial factor in ensuring the accuracy and reliability of the dynamic behaviour prediction of the structure. Modelling of bolted joints in indus...

Efficient and accurate analytical representation of bolted joints in an assembled structure for the prediction of the dynamic behaviour of the structure has been a crucial unsolved issue in the finite element (FE) community. 3D modelling of bolted joints, possessing a large number of degrees of freedom, leads to very high computational time. This p...

Bolted joints, which contribute significantly to minimise the magnitudes of resonant peaks of assembled structures and give easy-to-install and uninstall, have been widely used in various types of mechanical structural assembly and. However, modelling of an individual bolted joint within a large assembled structure has always been problematic, espe...

Accurate representation of the joint stiffness of bolted joints in the finite element (FE) model of a jointed structure is vital to ensure the accuracy and reliability of the predicted dynamic behaviour of the structure. The aim of this work was to put forward an efficient FE modelling method embodying the representation of the joint stiffness for...

Laminated rubber bearing is a significant device found in structures such as bridges and buildings. It is used to isolate the foundation and the superstructure from seismic loads. Since it is made up from a combination of rubbers and steel plates in alternate layers which make the laminated rubber bearing a complex material, the measurements of dam...