Stress analysis of a pinned wood joint by grey-field photoelasticity

Pinned (bolted) joints/connections are a widely used, but difficult to analyze, component. Their bolt/hole interface stresses are typically unknown a priori. Structural failures often initiate at connections and their contact stresses can be the “Achilles’ heel”. Although such connections are extremely prevalent in wood structures, ability to determine the individual stresses in mechanical wood joints is aggravated by the material’s orthotropy. Solutions to such non-linear problems that account for finite geometry, pin/hole friction and clearance are non-trivial. Many mechanical-joint analyses ignore friction for simplicity, but some contact friction is virtually always present. By applying a thin birefringent coating to the wood, the individual stresses and strains in the coating (and hence in the wood) are determined by synergizing grey-field photoelasticity, a stress function and boundary information. Full-field individual stresses are obtained in the wood, including at the contact boundary. Predicted strength based on the determined stresses is compatible with the connection failure.     

Stress distribution modeling for interference-fit area of each individual layer around composite laminates joint

The discussion about nonuniform stress distribution around interference-fit joint is particular significance in the design of composite laminates structures. In order to investigate the stress distribution of interference-fit area around composite laminates joint, an analytical model is developed for stress distribution based on the Lekhnitskii's complex potential theory. The normal and tangential stresses of contact are achieved by the relationship of deformation between pin and hole. The effects of ply orientation and interference percentage on stress components distributions of each individual layer around symmetrical laminates joint are discussed. In order to verify the validity of the analytical model, extensive 3D finite element models are established to simulate the stress components of laminates interference-fit joint. The results show that the analytical model is valid, and the laminate property and ply orientation have a significant effect on stress distribution trend while interference percentage mainly affects stress magnitude.     

Numerical study on tunnel damage subject to blast-induced shock wave in jointed rock masses

In this study, numerical modeling on the damage of existing circular tunnel subject to blast-induced shock wave was carried out with DEM-based code UDEC. The disturbed zones including failure zones, open zones and shear zones around circular tunnel and peak particle velocities (PPVs) at tunnel surface are employed to analyze the damage of tunnel. The effects of joint spatial and mechanical properties, initial stress of rock mass, and magnitude of shock wave amplitude to damage of tunnel were evaluated in this study. The difference of damage between non-supported circular tunnel and bolt-supported circular tunnel subject to the same blast-induced shock wave was also studied. It is found that the orientations of joints in rock mass around the tunnel have great effects on tunnel damage. The initial stress around tunnel has relatively small influence on tunnel damage. The bolt support could greatly increase the stability of tunnel by changing the vibration form of particle velocity rather than the decreasing of PPV.     

Microstructural and mechanical evaluation of a Cu-based active braze alloy to join silicon nitride ceramics

Self-joining of St. Gobain Si₃N₄ (NT-154) using a ductile Cu-Al-Si-Ti active braze (Cu-ABA) was demonstrated. A reaction zone (∼2.5-3.5 μm thick) developed at the interface after 30 min brazing at 1317 K. The interface was enriched in Ti and Si. The room temperature compressive shear strengths of Si₃N₄/Si₃N₄ and Inconel/Inconel joints (the latter created to access baseline data for use with the proposed Si₃N₄/Inconel joints) were 140 ± 49 MPa and 207 ± 12 MPa, respectively. High-temperature shear tests were performed at 1023 K and 1073 K, and the strength of the Si₃N₄/Si₃N₄ and Inconel/Inconel joints were determined. The joints were metallurgically well-bonded for temperatures above 2/3 of the braze solidus. Scanning and transmission electron microscopy studies revealed a fine grain microstructure in the reaction layer, and large grains in the inner part of the joint with interfaces being crack-free. The observed formation of Ti₅Si₃ and AlN at the joint interface during brazing is discussed.     

Fatigue Evaluation of Rib-to-Deck Welded Joints of Orthotropic Steel Bridge Deck

This study reported fatigue test results of 300-mm-wide specimens with three details: 80% partial joint penetration (80%PJP), weld melt-through (WMT), and both. The specimens were cut out from full-scale orthotropic deck specimens of 16-mm-thick deck plate. In the fatigue test, the deck plate was subjected to cyclic bending loading and the rib was free from loading. The fatigue fracture surfaces showed that the presence of WMT may affect the initiation of fatigue cracks. A propensity to root cracking rather than toe cracking was observed. Plotting fatigue test results in an S-N diagram showed that the specimens with WMT seemed to have slightly lower fatigue strengths than the 80%PJP specimens, but the difference is more likely to be within a usual scatter of test data, which means that both details have comparable fatigue strength. The present test results satisfied the S-N curves of JSSC-E (80?MPa at 2×106 cycles) or AASHTO-C (89?MPa at 2×106 cycles).     

Conceptual Design and Analysis of a Deployable Structure with Flexible Joints

The conceptual design of a self-deployable structure with flexible joints is presented in this paper. Joints store elastic energy in the folded, prestressed position and allow deployment until they are stopped by tendons. A study on a wire rope joint is first presented to determine its mechanical behavior with experimental, theoretical, and numerical approaches. An analysis is then performed on a bidimensional structure to propose the specific modeling of introducing prestress to the joints. The method is applied to a spatial system in an analysis that uses static equilibrium and kinematic deployment simulations. The results show good concordance among the different approaches.     

Improved Geometric Design of Bridge Asphalt Plug Joints

Asphalt plug joints (APJs) have several advantages over traditional bridge joints. They are easy and cheap to install and have good surface flatness. However, widespread application of APJs in bridges has been hindered by frequently observed premature failures. Detailed finite-element simulations are conducted to develop a better understanding of the parameters that influence APJ response under traffic and thermal loading conditions. The computational model employs a time and temperature dependent viscoplastic material model and is validated by comparing model results to previously published experimental data. The key parameters investigated are gap plate width, gap plate thickness, gap plate edge geometry, and geometry of the interface between pavement and APJ. The resulting information is synthesized into a proposed alternative APJ design that minimizes local demands deemed to be responsible for the observed early failures.     

Performance of bolted joints in Discontinuous Ceramic Cored Sandwich Structures – Static experimental testing

Thick section composites that consist of discontinuous ceramic tile arrays as a core represent a unique class of sandwich structures. They have been developed to provide a balance of structural, impact, and penetration resistance at minimum weight. Bolted joints are often used to fasten the Discontinuous Ceramic Cored Sandwich Structures (DCCSS) to other structures. Extensive experimental testing has been completed in order to better understand the performance of bolted joints in DCCSS. In this study, pin-loaded specimens are subjected to static in-plane tensile loading to establish the sequence and severity of failure modes and ultimate joint capacity. Static testing was completed on various geometric ratios such as edge distance effects, as well as the influence of tile gaps that exist in the discontinuous tile array. The results from this study establish guidelines for design of bolted joints in DCCSS.     

自走铁矿结构面的赤平极射投影分析

采用国际岩石力学学会推荐的详细线观测法对自走铁矿的节理裂隙进行了调查。用频率分布直方图统计了结构面间距和倾角。认为巷道为节理密集、发育的碎裂岩体。借助理正软件对调查数据进行分析,绘制出节理裂隙赤平极射投影极点等密度图和优势产状的分组表。将用于隧道稳定性判断的方法引入到巷道中,对自走铁矿的岩体稳定性进行了分析,认为节理对巷道的稳定性不利,建议巷道进行锚杆加固或喷砼等措施。