Mode Loading Conditions Research Articles

Analysis of peel and shear strains in cracked lap shear specimens subjected to fatigue loading using digital image correlation

Adhesive bonding presents many advantages, such as efficient manufacturing and improved structural performance [1]. However, in structures subjected to fatigue, cracks might initiate and propagate in joints, leading to in-service failure [2]. Most adhesively bonded joints are subjected to combination of peel and shear loads, so mixed I+II mode loading conditions are present [3]. In this work, Cracked Lap Shear specimens, which feature mixed I+II mode loading conditions, were tested under fatigue loading. During tests, crack growth was monitored using Visual Testing and Digital Image Correlation. With Digital Image Correlation, opening and sliding displacements in the bondline were extracted from the substrates’ displacement fields and compared against a Finite Element Model, revealing a highly strained process zone ahead of the crack tip. Results highlight the usefulness of DIC in capturing the deformation behaviour of adhesive joints under mixed mode loading conditions.

Investigation of Drift-based Damage Limit States for Historical Masonry Structures

ABSTRACT Drift-based performance assessment has been a practical tool among the research and engineering community. However, several studies showed that there are several critical issues such as seismic damage definitions and their quantifications related to the displacement-based approach when it is applied not only to modern masonry structures but also to historical ones. The main reason is due to (i) failure mode dependency, (ii) geometry, loading and boundary conditions, (iii) inadequate prediction of the failure modes based on in-plane capacity formulations given in the codes. The present article discusses the reliability of drift limit values proposed by different codes and guidelines by comparing drift values derived in two datasets of masonry piers through considering an application to a real case study. It is observed that performance-based assessment is mainly based on the failure mode of the masonry structure, while the Guideline for Earthquake Risk Management of Historical Structures in Turkey, which is widely used in practice, proposes drift limits that are independent of the masonry behavior. Without consideration of the behavior mode can lead to incorrect assumptions and hence unconservative performance assessment outcomes for the architectural heritage.

Enhanced sliding mode controller performance in DC-DC buck converter using a tan hyperbolic reaching law and constant plus proportional reaching law

This paper presents an enhanced sliding mode controller (SMC) operation, chattering analysis and loading conditions of the SMC DC-DC buck converter. Sliding mode portion, chattering attenuation are analyzed by using a conventional and proposed reaching law in buck converter. A proposed tan hyperbolic reaching law (THRL) is originated to be useful in terms of chattering mitigation and fast convergence. The major drawback of the conventional reaching law viz, it bypasses the main portion of the sliding mode portion to ensure fast reaching. It causes more chattering, more time to reach the steady state on the switching surface. The most significant improvement of SMC is that it guarantees strengthening the sliding mode phase. The proposed tan hyperbolic reaching law is being hit here during an exponential adjustment so that the attributes of it, covers complete sliding mode portion, chattering mitigation and fast reaching time. In turn, cause fewer switching loss in the buck converter. Even external disturbances and uncertainty of the system occurs. The loading conditions are applied to proposed tan hyperbolic reaching law and analyzed. Simulation analysis conducted by MATLAB/Simulink.

Investigation of Mechanical Behaviour of the Bone Cement (PMMA) under Combined Shear and Compression Loading

Generally, implants fixations in orthopedic surgery are insured by bone cement; which is generated mainly from polymer polymethylmethacrylate (PMMA). Since, the cement is identified as the weakest part among bone-cement-prosthesis assembly. Hence, the characterization of mechanical behaviour is of a crucial requirement for orthopaedic surgeon’s success. In this study, we investigates the failure behaviour of bone cement, under combined shear and compression loading, for the aim to determine the strengths of bone cement for different mode loading conditions. Therefore, experimental cylindrical specimens has been tested to assess different shear-compression stresses. Based on the mechanical tests, a finite elements model of cylindrical specimens was developed to evaluate stresses distribution in the bone cement under compression, shear and combined shear-compression loading. Results show that, the load which leading to the failure of the cement decreased with increasing of the specimen angle inclination with respect of loading direction.

On the interfacial constitutive laws of mixed mode fracture with various adhesive thicknesses

Interfacial toughness and interfacial strength, as two critical parameters in an interfacial traction–separation law, have important effect on the fracture behaviors of adhesively bonded joints. In this work, the global and local fracture tests are employed to investigate the effect of adhesive thickness on interfacial energy release rate, interfacial strength, and shapes of the interfacial traction–separation laws under the mixed I/II mode loading condition. Basically, the measured interface laws based on the single leg bending (SLB) specimens reflect the equivalent and lumped interfacial fracture behaviors which include the cohesive fracture, damage and plasticity. Several new and interesting experimental results were obtained. The experimentally determined interfacial traction–separation laws may provide valuable baseline data for the parameter calibrations in numerical models. The current experimental results may also facilitate the understanding of adhesive thickness-dependent interface fracture of bonded SLB joints.

The determination of fatigue crack propagation rates under mixed mode (I+III) loading

Abstract The problems of studying fatigue crack propagation under mixed mode (I+III) conditions are discussed in this paper. A method is proposed, based on the local mode I conditions existing at the crack tip, for predicting crack growth rates under mixed mode (I+III) conditions from pure mode I fatigue test data. Existing models and empirical expressions for mixed mode (I+III) fatigue thresholds and the path of crack propagation in angled crack three point end specimens for two mixed mode (I+III) loading conditions are used to demonstrate the procedure.