Modelling structural response of flexible plug expansion joints under thermal movements

The first natural frequency directly affects the operational conditions of compliant mechanisms in precision engineering systems. To address this challenge, a computational method based on the surface response method is proposed to optimize the frequency of a new one degree of freedom (DOF) compliant mechanism. Initially, a 1-DOF 3D model of a compliant mechanism is built. The dynamic equation and the frequency response are formulated via equivalent stiffness and the Lagrange method. Subsequently, a series of numerical simulations are conducted to find the fundamental frequency of the mechanism. The initial dimensions of the flexible joints are determined, and the initial frequency is analyzed by using finite element analysis. Next, the flexible joints in the designed mechanism are optimized by a variant of the genetic algorithm. The optimized dimensions of the mechanism are found with the thickness of the circular joint of 1.10 mm, the thickness of the leaf joint of 1.19 mm, and the length of the leaf joint of 54.50 mm. The optimized result showed that there is a significant improvement in the frequency of the mechanism, increasing from an initial design of 53.218 Hz to an optimal design of 75.927 Hz with an improvement of 42.6%. This study provides important reference materials for future research on compliant mechanisms.

This paper presents a finite-element (FE) model of a manipulator with a flexible link and flexible joint as well as embedded PZT actuators and proposes a corrected rebuilt reduced model (CRRM) to make its dynamic characteristics more consistent with reality and facilitate control design. The CRRM considers the holding torque of the manipulator driving motor and eliminates the response divergence induced by a fault of the mass matrix of the FE model. In order to reduce the dimensions and maintain the precision of the model, an iterated improved reduction system (IIRS) method is adopted. Additionally, a LQR controller is designed based on the output function of the improved model. The simulation results demonstrate that the CRRM is consistent with reality and the active controller has good performance in suppressing vibration of the manipulator with both the flexible link and the flexible joint.

In this study, a three-dimensional (3D) finite element model (FEM) consisting of an asphalt concrete (AC) overlay on top of jointed plain Portland cement concrete (PCC) slabs was developed to investigate the mechanism of the crack initiation of traffic-induced reflective cracking. Strain values at the bottom of AC overlay were the primary response obtained from the simulation results to represent the damage induced in the AC layer. Different bonding situations between the two layers, traffic load locations, material properties and thicknesses of the AC layer were taken into consideration. The analysis results show that the dominating strain for damage is dependent on the bonding condition between the AC and PCC layers. When the AC layer is completely bonded with the PCC layer, the damage will initiate firstly at the top of the joint corner between the PCC slabs to deteriorate the bonding, then the AC bottom will be susceptible to bending strain. It was observed that the most critical load location for modeling the case of fully bonded overlays is related to the AC thickness while in the case of partially bonded overlays, the most critical load location is always located on the top of one side of the PCC joint.

Asphaltic concrete lining for dams and storage reservoirs are today classified as state of the art technology. Storage reservoirs and dams are sealed with asphaltic concrete –world-wide. However, certain prerequisites are absolutely necessary for the successful use of this sealing method. First, there must be careful selection and suitability testing of the construction materials and then the subsequent elaboration of the mix composition for the various layers of the lining package. Professional placement and careful compaction are the critical impotence for the quality of finished lining. Asphaltic concrete as an impervious material is used in many countries for more than 60 years. In the Arab region, the asphaltic concrete is used in Syria, Oman, Algeria, Iraq, UAE and Saudia Arabia for sealing of dams and storage reservoirs. The first use of asphaltic concrete in Syria was the sealing of Al Sourani dam in Tartus by the use of asphalt facing with inclination of 1:2.25. The construction of the asphalt facing was finished in November 2003. In this paper, we shall explain the property of the construction materials, lining design, quality control, and thermal condition in such semi-arid area. Key words: Asphalt, dams, testes, construction materials, bitumen.

The response of bridges exposed to thermal environment conditions is studied. Analytical methods are developed to obtain temperature distributions and the maximum bridge temperature ranges. Thermoelastic analysis is conducted to obtain the temperature induced movements and the associated stresses in bridges. Parametric studies are conducted for different bridge geometries, temperature distributions, and support conditions. A field test is conducted on a bridge to verify the analytical models. The analysis suggests that concrete bridges sometimes are designed for smaller temperature ranges and corresponding thermal movements than may be expected in practice. The analysis suggests that steel bridges with composite concrete decks sometimes are designed for larger temperature ranges and thermal movements than may be expected at many locations in the United States. Skew and curved bridges often exhibit magnitude and direction of movement that is different than commonly expected. Additional guidelines and recom...

Mechanisms of flexible pavement fatigue cracking and reflective cracking from a cement-treated base (CTB) layer were investigated. 3D finite-element (FE) models were developed to simulate typical pavement structures for low-, medium-, and high-volume traffic. The FE models simulated a dual-tire assembly as well as surface vertical and tangential contact stresses. The FE model was validated using stress and strain measurements obtained from the Louisiana Accelerated Loading Facility. The shrinkage strain induced by a CTB layer was converted to displacement in the base layer and was used to simulate the tensile stresses caused by shrinkage cracking. Results showed that the initiation of surface fatigue cracking is due to vertical shear strain within the AC layer exacerbated by high tensile strain at the surface due to loading. Furthermore, the incorporation of transverse tangential stresses increased the surface tensile strains by more than 50% regardless of the asphalt concrete (AC) layer thickness. However, longitudinal tire contact stresses had minimum effect (less than 10%) on the surface and bottom AC tensile strains. Tensile stresses due to shrinkage strains in the CTB were observed to be higher than the tensile strength of the material after a few weeks of curing, suggesting the potential initiation of shrinkage cracks shortly after construction. The addition of fly ash to the CTB may significantly reduce reflective cracking potential after construction.

A computational parametric study leading toward the development of a new type of low-damage precast concrete segmental column for accelerated bridge construction in seismic areas is outlined. In contrast to conventional monolithic concrete construction, accelerated bridge construction significantly reduces on-site construction time, total project delivery time, weather-related construction delays, and environmental impact, and it provides improved work zone safety for the traveling public and contractor personnel and high product quality and durability. Low-damage systems provide significantly reduced postearthquake downtimes, repair costs, and casualties. The proposed column design will incorporate internal unbonded posttensioning and flexible joints at the column ends, where large flexural demands occur. These joints will be (flexurally) deformable enough to accommodate large column lateral deformations (drift ratios of 10% or higher) without damage, and (axially) stiff enough to limit initial axial deformations due to initial posttensioning and gravity loads. To investigate this concept, a three-dimensional finite element model of a cantilever segmental concrete column incorporating a flexible joint segment at the bottom was generated, and a comprehensive parametric study was conducted. The parametric study investigated three types of polyurethane elastomers for the flexible joint and various geometric properties of the flexible joint in reference to the column geometry. The findings of this study, as supported by preliminary material testing, have shown that hyperelastic materials, such as stiff rubbers and polyurethanes, are good candidates for the proposed application.

Thoracolumbar kyphosis (TLK) secondary to Scheuermann's disease often leads to low back pain, which may be related to altered biomechanical properties of the spine. However, There is a lack of biomechanical studies in the literature that comprehensively evaluate tissue-level stresses and strains in the thoracolumbar spine affected by Scheuermann's kyphosis, particularly during functional motions such as forward flexion. This study analyzed biomechanical changes during forward flexion in TLK patients using musculoskeletal dynamics and finite element modeling. Twenty TLK patients and twenty healthy individuals were recruited. Kinematic data (joint angles), kinetic data (joint reaction forces and moments), and electromyographic (EMG) data were collected at different bending angles using Vicon 3D motion capture and surface electromyography. Physiologic motions captured from in vivo experiment was simulated using OpenSim, with inverse dynamics and optimization used to calculate vertebral joint angles, muscle forces, and intervertebral reaction forces, serving as boundary conditions for ANSYS finite element models. Subject-specific finite element models for both groups were constructed in ANSYS using computed tomography (CT) DICOM files. The CT-based finite element models were used to compute von Mises stress distributions-a mechanical parameter indicating combined tissue stress and potential risk of overload-in the vertebral body, intervertebral discs, and articular cartilage at different forward flexion angles under the applied loadig conditions. At different forward bending angles, TLK patients exhibited high stress distribution in the L1-S1 segment vertebral articular processes. Compared with healthy individuals, the stress distribution in the S1 segment was uneven, with peak stress reaching up to to 2.8 times higher (180% increase) than that of healthy individuals. TLK patients exhibit stress concentration in the annulus fibrosus region of the intervertebral disc, while the stress distribution in the nucleus pulposus region is relatively uniform. The peak stress in the intervertebral disc during different movements can be up to 2.33 times higher (133% increase) than in healthy individuals. In TLK patients, stress concentration was observed in the articular cartilage of all segments except for the L5/S1 segment. The peak stress in the articular cartilage during different movements was up to 12.02 times higher (1,102% increase) than in healthy individuals. These results suggest that TLK patients experience elevated and uneven spinal tissue stress during forward flexion, which may contribute to increased risk of degeneration and back pain.

This study investigated the effects of moderate daily temperature variations on reflective cracking in asphalt concrete (AC) overlays on Portland cement concrete (PCC) pavements using three-dimensional (3D) finite element (FE) modeling. The FE model consists of an AC overlay on top of PCC slabs, followed by aggregate base and subgrade. The year-round temperature variations were divided into discrete groups using a clustering technique and each group was applied separately in the FE model. The maximum stress and strain values associated with each temperature variation group were determined using the FE model and used as the driving force corresponding to the thermally induced damage in the AC overlay. The results show that the maximum stress and strain values in the overlay depend on the hourly temperature variation as well as the seasonal temperature profile. The daily temperature variation controls the deformation of the underlying PCC slabs, whereas the seasonal temperature profile determines the viscoelastic properties of the AC overlay. The estimated maximum tensile stress and strain values suggest that the AC overlay is primarily subjected to damage from repetitive thermal loading instead of one-time fracture events for moderate temperature variations. In addition, when the AC overlay is fully bonded to the PCC slabs, the thermal strains are much greater than the traffic induced strains, indicating a high possibility of thermal reflective cracking being the dominant damage mechanism for these cases.

The fracture behavior of lead-free solder joints has been shown to be influenced by the level of constraint on the joint deformation. The joint constraint is a measure of joint size/geometry, adherend stiffness and loading type. Among these parameters, there is no data on the effect of solder joint width (i.e. joint size in the out-of-plane dimension) in spite of its possible role in defining the degree of solder joint deformation. The fracture load of 2.5 mm long SAC305 solder joints with a thickness of 250 μm was measured under mode I intermediate strain-rate loading (0.03 s -1 ) for three different widths of 8, 11 and 14 mm using Cu-solder-Cu double cantilever beam (DCB) specimens. The adherend thickness was 14 mm in all the cases. A hydraulic tensile testing machine with a cross-head speed of 5 mm/s was employed with the failure of the solder joints evident as an abrupt drop in the load cell output. The fracture load over the width of the specimen, F/w , was then measured and the critical strain energy release rate for crack initiation, J ci , of the solder joint was calculated using a finite element model (FEM). The fracture load increased by almost 75% from a solder width of 8 mm to 14 mm, while F/w changed only by 10% over this range. The statistical analysis on the three groups showed that this difference was statistically insignificant. Also, J ci remained almost unchanged with the joint width suggesting that the data obtained from each width can be used to predict the fracture loads of the solder joints having different widths. This promising conclusion can be applied to real ball grid array (BGA) solder joints used in microelectronic package-on-board systems subject to bending type of loading.

Influence of pressure and deflection loads on the critical behavior of flexible joints

A reliable and accurate analytical model is desired for the printed circuit board (PCB) with IC package to predict the system response due to loadings such as shock and vibration simulation or even with thermal effect. This work addresses the procedure of model verification by the adoption of experimental modal analysis (EMA) to validate the finite element (FE) model constructed by FE commercial software. The PCB with one package adhered with the heating pad to emulate the heat effect is first considered for completely free boundary condition. The refined FE model of the PCB consists of detail components, such as the chip, substrate, compound and solder balls. The thermal effect on the PCB is simulated to conduct the temperature field analysis as well as the thermal stress. The modal analysis on the PCB with the heating in steady state is then performed to obtain the structural modal parameters, i.e. natural frequencies and mode shapes. The EMA is also carried out to determine the system modal properties that are used to update the analytical FE model. Through the comparison of frequency response functions and modal parameters between the analytical FE model and the real PCB structure, the refined FE model can be verified for material properties and thermal boundary conditions. The same procedure for model verification is then conducted via both EMA and FEA on the PCB in the fixed boundary that complies with the test fixture for the random vibration test of JEDEC specification. The verified equivalent FE model of the PCB can then be adopted to perform spectrum response analysis accordingly.

Railroad structural behaviour is a significant factor for safety and comfort during high-speed train operation. Intending to improve railway performance, increase its bearing capacity, and reduce vibrations induced by train passage, asphalt concrete has become a material to be integrated into railway construction. Despite several studies evaluating asphalt concrete effect on the railway mechanical behaviour, its impact assessment remains poorly understood. This study investigates the impact of asphalt concrete material in the geogrid-reinforced-pile-supported embankment structure subjected to high-speed train moving. A 3D nonlinear finite element model was developed to simulate Harbin (Dalian (China) instrumented railroad test section accurately. The high-speed train moving load was modelled as a transitory dynamic load via a user-defined subroutine 3D load in which the track irregularity is incorporated. The established model was effectively validated by the vibration acceleration and stress measured in the field test section. The asphalt concrete viscoelasticity behaviour was incorporated into the 3D geogrid-reinforced-pile-supported embankment finite element model through the Prony series to characterise its mechanical response better. The impact of asphalt concrete material in maintaining a low and constant structural vibration, regardless of train weight level, moving speed variations, and weather conditions were investigated, analysed and discussed.

In Friction Stir Lap Welding(FSLW), the movement of material within the weld was more important than the microstructure, due to the interface present between the sheets. Thus, The soundness of free defect, Effective Sheet Thickness(EST) and width of joint were most important factor of mechanical properties. Specimens by lap joint types that were 'A-type' and 'R-type' were made in this study. A-type tensile specimen was loaded at advancing side and R-type tensile specimen was loaded at retreating side. Macro-, micro-structural observation and mechanical properties of FSLW A5052-H112 alloy ware investigated under varying rotating and welding speed. The results were as follows: Material hook formed decreasing after sharply increasing was appeared at the end interface of joint area in advanced side, and material hook formed decreasing after smoothly increasing was observed at that in retreated side. Tensile load had no relation with defects. As rotating speed was higher, tensile strength was increasing and EST was decreasing regardless of joint types. joint efficiency was over 70%. In a result of fractography, fracture in A-type was partially occurred by dimple in SZ, and fracture in R-type was generally occurred by dimple in HAZ.

The state of stress under tension-shear load was investigated experimentally and analytically on the single spot welded lap joint of single shear splice.Specimens were made from mild steel sheet of 1.0mm thickness. The stress distributions on the surfaces of the specimen were examined experimentally by the brittle coating and strain gage methods.According to the experimental results, the state of stress in the joint under tension-shear load appeared to be determined by the following factors.(i) Plane stress distribution near the weld nugget caused by the local transmission of load.(ii) Bending in the longitudinal direction resulted from the offset of lapped plates.(iii) Bending in the transverse direction, occured secondarily by the superposed effect of factors (i) and (ii).To clarify the state of stress owing to factor (i), the plane stress distribution was examined by the experiments on the middle plate of single spot welded double shear lap joint in tension, which was not affected by bending. Two-dimensional analysis by the finite element method was also made of the assumption of the idealized“Plane Model”.In connection with the state of stress due to longitudinal bending (factor (ii)), two-dimensional finite element analysis was employed on the“Section Model”of single spot welded single shear lap joint.Finally, the experimental stresses on the single spot welded single shear lap joint were compared with the analytical values, which were obtained by superposition of the stresses computed by Plane and Section Models.The results obtained are as follows:(1) In the stress measurement on the single spot welded single shear lap joint, the peak stress at 3mm distant above the nugget edge attained the value 3.9 or -1.3 times of the nominal tensile stress on the inner or outer surface of lapped plate, respectively.(2) The plane stress distribution computed by Plane Model agreed fairly well with the experimental result observed on the middle plate of double shear lap joint. In the finite element analysis by Plane Model, the lapped plates of the joint were doubly defined in the same plane.(3) The stress concentration factor deduced from the plane stress distribution was 2.2∼2.3 at the nugget edge of the joint, where the width of joint was 25mm and the nugget diameter was 5φ.(4) At the representative positions on the inner and outer surfaces of single shear lap joint, the superposed values of the stresses computed on the factors (i) and (ii) corresponded well with the axial stresses obtained from the experiments.