Joint Material Properties Research Articles

Characterization of joint contact model considering friction of variable stator vane mechanism and application to principle-level mechanism

For the characterization of joint contact model of the variable stator vane (VSV) mechanism, the dry friction properties of joint materials must be taken into account. In this paper, the important parameters characterizing the joint contact model are experimentally tested, and then the characterized contact model containing the parameters is utilized for the dynamic analysis of a principle-level VSV mechanism test rig, including the dry friction rotary pair. Firstly, the friction tests and the vibration tests induced by the friction process are carried out. Then an ideal comprehensive dynamic model of the scaled system of VSV mechanism’s single kinematic chain is established through the Lagrange multiplier method. The friction coefficient values obtained from the test are embedded into the contact force model considering friction factors and compared with other macro models. The accuracy of the hybrid contact model is verified through a one-shot contact-impact simulation and the corresponding displacement is measured for evaluation with accuracy of established ideal dynamic model. Finally, the influence of different driving methods on the dynamic characteristics of the system is analyzed.

Study on Stress Evolution and Crushing Behavior of Jointed Rock Mass under Confining Pressure and Joint Materials

To study the effects of confining pressure and joint material properties on stress evolution and fracture behavior of jointed rock mass under SHPB impact load, the numerical software LS-DYNA and the indoor SHPB impact system are used to carry out experimental research on intact rock mass and jointed rock mass. The peak stress, reflection and transmission coefficient, and specimen failure state of rock specimens under different schemes are obtained. The effects of confining pressure level and joint material properties on the propagation and attenuation law of explosive stress waves are expounded. The test results show that when the confining pressure is within a specific range, the impact resistance of the limestone specimen can be increased, and the more difficult it is to be destroyed. Moreover, if the confining pressure continues to increase after rising to the peak value, the impact resistance of rock specimens will decline. In that case, the impact resistance of the specimen will decrease—the dynamic strength of jointed rock mass changes with a change in joint material. The dynamic strength of cement jointed rock is the highest, that of gypsum jointed rock is the second, and that of epoxy resin jointed rock is the lowest. The impact damage resistance of the jointed rock has the same law as the above.

Novel design of inter-module joint in reinforced concrete modular construction using high-strength fiber-reinforced cementitious composites (HSFRCC)

The development of modular construction is surging in recent years. It has been popularized worldwide due to better quality control, environmental-friendliness and potential construction time and cost savings. A specific challenge associated with reinforced concrete modular construction is the design of inter-module joint. Minimizing the size of in-situ cast joint between prefabricated units is of great importance for improving construction efficiency. In addition, reinforcement details should be as simple as possible to enhance constructability. This study proposes a novel connection design for wall-to-wall inter-module joint using high-strength fiber-reinforced cementitious composites (HSFRCC) and steel plate-induced confining stresses. Small-scale direct tension pull-out tests were performed with specially designed loading fixtures to simulate the bond behavior between HSFRCC and high-yield steel bars in the proposed joint design. The effects of joint material properties, embedment length and confinement conditions were evaluated. Results showed that the combined use of HSFRCC with plate confinement greatly improves bond capacity. The preferred rebar yielding failure (rather than bond failure) was achieved with embedment length of only 8d (d being the bar diameter). A rigorous finite element model was established by incorporating explicit geometry of rebar and mechanical properties of joint material, and the numerical results showed good agreement with test observations. Therefore, the applicability of the FE analysis in facilitating the proposed inter-module joint is demonstrated.

A roughness parameter considering joint material properties and peak shear strength model for rock joints

This study aims at proposing a reasonable roughness parameter that can reflect the peak shear strength (PSS) of rock joints. Firstly, the contribution of the asperities with different apparent dip angles to shear strength is studied. Then the shear strength of the entire joint asperities is derived. The results showed that the PSS of the entire joint asperities is proportional to a key parameter θτ, which is related to the geometric character of the joint surface and the joint material properties. The parameter θτ is taken as the new roughness parameter, and it is reasonable to associate the PSS with the geometric characteristics of the joint surface. Based on the new roughness parameter and shear test results of 20 sets of joint specimens, a new PSS model for rock joints is proposed. The new model is validated with the artificial joints in this paper and real rock joints in published studies. Results showed that it is suitable for different types of rock joints except for gneiss joints. The new model has the form of the Mohr-Coulomb model, which can directly reflect the relationship between the 3D roughness parameters and the peak dilation angle.

NUMERICAL ANALYSIS OF WELDED BEAM-COLUMN JOINTS IN ALUMINUM STRUCTURES

The objective of this study is to compare the performance for welded beam-column joints in aluminum structures using moment-rotation diagrams and to evaluate the influence of welding on joint rigidity. A nonlinear numerical calculation of welded beam–column joints is performed using the finite element method. Material and geometric nonlinearities were included in the model. The connection was analyzed for two cases: variants with and without welded stiffener plates. Two material models were used. The first was derived from the applicable standard for aluminum structures, while the other was based on the results of a previous material study and calibrated using a separate numerical calculation. From the results of the calculations, moment-rotation diagrams for different geometries and material properties of joints were constructed and compared. The obtained moment-rotation diagrams for the stiffened and unstiffened joints demonstrate that stiffening of the joints in aluminum structures improves the properties of the joint in terms of higher rigidity, resistance, and ductility, regardless of the existence of the heat affected zone.

Nonlinear ultrasonic evaluation of high-density polyethylene natural gas pipe thermal butt fusion joint aging behavior

High-density polyethylene (HDPE) pipes are widely used in urban natural gas pipelines. Thermal butt fusion (BF) welds are the weakest components of pipelines. Welding joint aging causes degradation of the PE thermal BF joint material properties. Using the nonlinear ultrasonic technique as a nondestructive testing (NDT) method was proposed for evaluating aging damage. Nonlinear ultrasonic measurements were conducted for HDPE thermal BF joint samples exposed to compression creep. Ultrasonic harmonics are generated due to aging damage. The acoustic nonlinearity parameter β based on the fundamental and second harmonics is calculated. The results indicate that β is sensitive to the variation in HDPE specimens under different aging conditions. This NDT method is useful in tracking microstructural changes in BF joints due to aging during the service process.

Temperature and strain-rate dependent constitutive model for prediction of thermal cycling life

With temperature cycling as the characteristic working environment of aerospace electronic chips, various constitutive models have been proposed to predict the failure problems of solder joints. However, most researchers adopted only a set of constant parameters to describe the solder joint material properties throughout the temperature cycles, which is obviously unreasonable concerning the possible wide range of working temperature. In fact, with the changing temperature and strain rate, some material parameters will correspondingly evolve as observed in the experiments. In this paper, the framework of the Anand constitutive model is adopted to verify the effect of material parameters of different temperatures and strain rates on the mechanical properties of materials under the scenario of temperature cycling. The lead-containing solder alloy 63Sn37Pb material that is most widely used in aerospace is selected as the solder material for the interconnection structure. In addition, a typical plastic ball grid array (PBGA) packaging structure is used to analyze the influence of the constitutive model parameters on the PBGA thermal fatigue life. Based on experimental data, seven sets of constitutive model parameters with different temperatures (-55°C~125°C) under a region of low strain rate (1×10-4/s) were employed to compare the mechanical properties of the material under temperature cycling. The sensitivity analysis of material parameters is performed and the underlying mechanism are also explained so that the present study can promote the optimization of the constitutive model in numerical simulations in practice.

A modified analytical model for stress analysis of adhesively bonded stepped-lap joints under tensile load

A modified analytical model with closed-form solution is proposed in this study to investigate interfacial shear and normal stresses in adhesively bonded double-lap joints with stepped outer adherend, subjected to tensile loading. By extending some researchers' prior related works, explicit expressions for adhesive interfacial shear and normal stresses are derived, with considerations of shear deformation in the adherends and plasticity in the adhesive layer. Continuity conditions are introduced to fit the variation of the outer adherend thicknesses. To obtain unknown constants of general solutions for adhesive normal stress, some approximate boundary conditions are reconstructed and several simplifications are imposed. The adhesive stress distributions along the bondline are obtained to investigate the effects of joint's material properties and geometric parameters. Adhesive with elastic-perfect plastic behavior is also considered in the analyses. The results obtained from the present model show an excellent agreement with corresponding finite element results. The present method is applicable to implement parametric analysis and optimal design for adhesively bonded double-lap joint.

Behavior of stress generated in semiconductor chips with high-temperature joints: Influence of mechanical properties of joint materials

High-temperature joint materials are indispensable to realizing next-generation power modules with high-output performance. However, crack initiation resulting from stress concentration in semiconductor chips joined with high-temperature joint materials remains a critical problem in high-temperature operation. Therefore, clarifying the quantitative influence of joint materials on the stress generated in chips is essential. This study investigates the stress behavior of chips joined by Ni–Sn solid–liquid interdiffusion (SLID), which results in a high-temperature joint material likely to generate cracks after joining or when under thermal cycling. The results are compared with those fabricated using three types of solders, Pb–10%Sn, Sn–0.7%Cu, and Sn–10%Sb (mass %), which are conventional joint materials with different melting points and mechanical properties. Using Ni–Sn SLID results in the generation of high compressive stress (500 MPa) without stress relaxation after the joining process in contrast to the case of solders in which the compressive stresses are low (<300 MPa) and decrease to still lower levels (<250 MPa). In addition, no stress relaxation occurs during thermal cycling when using Ni–Sn SLID, whereas stress relaxation is clearly observed during heating to 200 °C using solders. Different stress behaviors between Ni–Sn SLID and other joint materials are illustrated by their mechanical strength and resistance against plastic and creep deformation. These results suggest that stress relaxation in a chip is key in suppressing crack initiation in highly reliable modules during high-temperature operation.

Non-linear static behaviour of ancient free-standing stone columns

This work investigated the non-linear behaviour of ancient natural stone columns in the Mediterranean region made from multiple blocks or ‘drums’. A two-dimensional custom-made computational model based on the discrete-element method was employed. In the numerical model, the columns were represented as an assemblage of distinct blocks connected together by zero-thickness interfaces, which can open and/or close depending on the magnitude and direction of the stresses applied to them. Through non-linear static analysis, capacity curves and corresponding failure mechanisms of each of the studied models were obtained. The influence of different parameters (the number of drums, geometrical properties and imperfections at columns) was also assessed to observe their influence on the response of drum assemblies. The results of analyses revealed that rigid overturning is the main collapse mechanisms under uniform horizontal forces. A combination of rigid and shear failure mechanisms might also occur, depending on geometric characteristics and the choice of joint material properties. A higher displacement capacity was observed for columns constructed with a larger number of drums. It was also found that imperfections in the ancient free-standing columns have a significant influence on the lateral load resisting capacity. Therefore, structural analysis of undamaged columns may not represent the actual capacity of the columns due to their very sensitive and highly non-linear characteristics.

Optimization of Laser Keyhole Welding Strategies of Dissimilar Metals by FEM Simulation

Laser keyhole welding of dissimilar metals has been simulated to study the effect of welding strategies (laser beam displacements and tilts) and combination of metals to be welded on final quality of the joints. Molten pool geometry and welding penetration have been studied but special attention has been paid to final joint material properties, such as microstructure/phases and hardness, and especially to the residual stress state because it greatly conditions the service life of laser-welded components. For a fixed strategy (laser beam perpendicular to the joint) austenitic to carbon steel laser welding leads to residual stresses at the joint area very similar to those obtained in austenitic to martensitic steel welding, but welding of steel to Inconel 718 results in steeper residual stress gradients and higher area at the joint with detrimental tensile stresses. Therefore, when the difference in thermo-mechanical properties of the metals to be welded is higher, the stress state generated is more detrimental for the service life of the component, and consequently more relevant is the optimization of welding strategy. In laser keyhole welding of austenitic to martensitic stainless steel and austenitic to carbon steel, the optimum welding strategy is displacing the laser beam 1 mm toward the austenitic steel. In the case of austenitic steel to Inconel welding, the optimum welding strategy consists in setting the heat source tilted 45 deg and moved 2 mm toward the austenitic steel.

가상 생체외 사체 실험용 경추 다물체 동역학 모델 개발

In this study, a multibody dynamic model of the cervical spine was developed for a virtual in-vitro cadaveric experiment. The dynamic cervical spine model was reconstructed based on Korean CT images and the material properties of joints and soft tissue obtained from in-vitro experimental literature. The model was validated by comparing the inter-segmental rotation, multi-segmental rotations, load-displacement behavior, ligament force, and facet contact force with the published in-vitro experimental data. The results from the model were similar to published experimental data. The developed dynamic model of the cervical spine can be useful for injury analysis to predict the loads and deformations of the individual soft-tissue elements as well as for virtual in-vitro cadaveric experiments.

Effect of intercostal muscle and costovertebral joint material properties on human ribcage stiffness and kinematics

Current finite element (FE) models of the human thorax are limited by the lack of local-level validation, especially in the ribcage. This study exercised an existing FE ribcage model for a 50th percentile male under quasi-static point loading and dynamic sternal loading. Both force-displacement and kinematic responses of the ribcage were compared against experimental data. The sensitivity of the model response to changes in the material properties of the costovertebral (CV) joints and intercostal muscles was assessed. The simulations found that adjustments to the CV joints tended to change the amount of rib rotation in the sagittal plane, while changes to the elastic modulus and thickness of the intercostal muscles tended to alter both the stiffness and the direction and magnitude of rib motions. This study can lend insight into the role that the material properties of these two thoracic structures play in the dynamics of the ribcage during a frontal loading condition.

Experimental/Numerical Analysis of Thermally Induced Warpage of Ultrathin Chip-on-Flex (UTCOF) Interconnects

Future applications of flexible displays and wearable electronics will need 3-D stacked flexible interconnects. The interconnection of an ultrathin chip-on-flex (UTCOF) that can provide flexibility is one approach that meets this requirement. Therefore, thermally induced warpage of UTCOF interconnects using anisotropic conductive adhesive (ACA) is investigated. In this paper, the effects of the ACA joint material properties, bonding temperature, and chip thickness on warpage of ACA-bonded UTCOF interconnects are examined experimentally and numerically. Two film types of ACA materials, ACA-P and ACA-F, are assembled under different bonding temperatures to study the effects of bonding temperature on warpage via out-of-plane deformation measurements using a micro figure measurement instrument. Micro Au-bump and compliant-bump assemblies in 80-μm-pitch dummy test vehicles are evaluated. Moreover, ultrathin chips with 25-50 μm thickness were assembled onto polyimide flex substrates to study the effects of chip thickness on thermally induced warpage. The 85°C/85% relative humidity thermal humidity storage test (RH THST) was also conducted for 1000 h for the UTCOF assembled with the selected process parameters. The interfaces between the ultrathin silicon chip and substrate are inspected in cross-sectional scanning electron microscopy (SEM) images. To validate the results of the experiments, a rigorous 3-D finite element (FE) analysis model integrating both thermal and thermal-mechanical behaviors of the UTCOF is established and performed using the ANSYS program. Experimental and numerical results indicate that the warpage of the micro compliant-bump assembly is less than that of the micro Au bump. Furthermore, the averaged warpage of the ACA-P-bonded samples with the Au bump using a 50- μm-thick chip is around 50.3 μm at a bonding temperature of 160°C whereas that of the ACA-F-bonded samples is 64.4 μm at 190°C. Additionally, both thermal expansion mismatch and the thermal gradient between the ultrathin silicon chip and substrate strongly affect the thermal-mechanical behaviors of the UTCOF interconnects. As expected, warpage increases as thickness of an ultrathin silicon chip decreases. A strong correlation exists between FE analysis results and experimental results. The manufacturing technology for high-density and flexible UTCOF interconnects with ACA joints is thus established.

A three-level non-deterministic modeling methodology for the NVH behavior of rubber connections

Abstract Complex built-up structures such as vehicles have a variety of joint types, such as spot-welds, bolted joints, rubber joints, etc. Rubber joints highly contribute to the nonlinear level of the structure and are a major source of uncertainties and variability. In the general framework of developing engineering tools for virtual prototyping and product refinement, the modeling of the NVH behavior of rubber joints involve the computational burden of including a detailed nonlinear model of the joint and the uncertainties and variability typical of that joint in a full-scale system model. However, in an engineering design phase the knowledge on the joint rubber material properties is typically poor, and the working conditions a rubber joint will experience are generally not known in detail. This lack of knowledge often do not justify the computational burden and the modeling effort of including detailed nonlinear models of the joint in a full-scale system model. Driven by these issues a non-deterministic numerical methodology based on a three-level modeling approach is being developed. The methodology aims at evaluating directly in the frequency domain the sensitivity of the NVH behavior of a full-scale system model to the rubber joint material properties when nonlinear visco-elastic rubber material behavior is considered. Rather than including directly in the model a representation of the rubber nonlinear visco-elastic behavior, the methodology proposes to model the material nonlinear visco-elastic behavior by using a linear visco-elastic material model defined in an interval sense, from which the scatter on the full-scale system NVH response is evaluated. Furthermore the development of a multi-level solution scheme allows to reduce the computational burden introduced by the non-deterministic approach by allowing the definition of an equivalent linear interval parametric rubber joint model, ready to be assembled in a full-scale system model at a reasonable computational cost. By using a commercial finite element code the developed methodology is illustrated through a numerical case-study: the low-frequency dynamic analysis of automotive door weather-strip seals.

Microstructural evolution and hardness changes in the interface of Cu/316L joint materials under aging and ion irradiation

The effects of aging and ion irradiation on microstructure stability and hardness change in the joint materials of CuNiBe/316L and CuAl25/316L have been investigated in the present study. The aging at 673 K for 1000 h or Ni ion irradiation at 573 and 673 K to 10 dpa did not promote the interdiffusion and void swelling at the interface. The hardness in both Cu alloys and stainless steel was increased by irradiation, however, it was decreased by aging except for CuNiBe alloy. The hardness change in CuNiBe alloy was larger than that in CuAl25 alloy. The hardness changes would have a significant effect on the mechanical properties of joint materials.

Fracture aspects of adhesive joints: material, fatigue, interphase, and stress concentration considerations

—The effects of secondary material phases added or created in the adhesive bulk during processing ; changes in joint material properties due to processing and adhesion (interphase properties) and/or loading, including fatigue loading; and effect of interphase material properties on overlap edge stress concentrations are considered in this paper in relation to the fracture behavior of adhesive joints. A theoretical discussion is provided on each of these issues along with specific examples and experimental and/or calculated data. The experimental data discussed were obtained using bulk specimens (material considerations), independently loaded mixed-mode specimens (ILMMS) (fatigue/fracture considerations), and single fiber fragmentation specimens (interphase considerations and its effect on the overlap edge stress concentration). Cause-effect relations between the above-mentioned fracture issues are highlighted as permitted by the data and the analytical models presented.