Abstract
One of the primary causes of a decrease in strength in adhesive joints is the presence of stress
concentrations at the ends of the overlap region. To address this issue effectively, the bi-adhesive technique has been
introduced to minimize stress concentrations at the overlap ends. Several research efforts have been devoted to
studying single lap adhesive joints. However, this type of assembly exhibits stress concentrations at the ends of the
joint, in contrast to its inactive core. The aim of this research is to present a numerical analysis of single lap biadhesive
joints using cohesive zone models with four different adhesives. Two adhesives of the same chemical
composition, one rigid and one flexible, were used. The overlap length parameters for each adhesive area were
considered. Thus, the placement of both rigid and flexible adhesives was optimized. The combination of both
adhesives in a single lap adhesive joint, with the more rigid adhesive positioned at the core of the joint, provided
enhanced strength to the assembly with a 37% improvement. The variation in overlap length of the adhesives in the
bi-adhesive joints affected the joint toughness. Among them, the best results were obtained when covering 40% to
60% of the overlap length with the more rigid adhesive at the core of the joint.
Key Words
bi-adhesive joint; cohesive zone models; failure; single lap joint
Address
Mohammed C. Ezzine: Department of Mechanical Engineering, Mustapha Stambouli University of Mascara, 29000 Mascara, Algeria;
Laboratoire Mécanique Physique des Matériaux, Department of Mechanical,
Djillali Liabes University 22000 Sidi Bel Abbes, Algeria
Ilias M.A. Ghermaoui: Laboratoire Mécanique Physique des Matériaux, Department of Mechanical,
Djillali Liabes University 22000 Sidi Bel Abbes, Algeria
Kawther F.Z. Ezzine: Department of physics, Faculty of Exact Sciences, Djillali Liabes University 22000 Sidi Bel Abbes, Algeria
Mohamed Mokhtari: Laboratoire LaRTFM, Ecole Nationale Polytechnique Maurice Audin, 31000 Oran, Algeria
Abstract
This paper investigates the elastic instability behavior of sandwich beams featuring functionally graded
skins and functionally graded porosity distribution of ceramic (Type-A) or metal (Type-B) core. Employing a
high-order quasi-3D beam theory and the principle of virtual work, we derive the governing stability equations. The
analysis considers three distinct porosity distributions (FGP) across the thickness, capturing variations in elastic
modulus. The functionally graded porosity (FGP) distributions in functionally graded material (FGM) sandwich
beams offer significant mechanical advantages over traditional porosity patterns. FGP facilitates the graded
customization of stiffness, strength, and vibration response through the thickness, thereby optimizing weight and
energy absorption while minimizing adverse effects, such as excessive deflection or diminished load capacity. This
methodology enhances the overall structural performance and design. A parametric study evaluates how slenderness
ratio, porosity volume fraction, aspect ratio, power-law grading index, and boundary conditions affect the critical
buckling load (CBL). Numerical solutions are obtained and compared with existing higher-order shear deformation
theories and full 2D/3D models, confirming the accuracy and robustness of the present approach.
Key Words
critical buckling load; elastic instability; functionally graded porosity (FGP); principle of
virtual work; sandwich beams
Address
Aissam Messaoudi, Mourad Chitour: 1Department of Mechanical Engineering, Faculty of Sciences & Technology,
University Abbes Laghrour, Khenchela 40000, Algeria
Abdelhakim Bouhadra, Abderrahmane Menasria: Department of Civil Engineering, Faculty of Sciences & Technology,
University Abbes Laghrour, Khenchela 40000, Algeria;
Materials and Hydrology Laboratory, University of Sidi Bel Abbes, Faculty of Technology, Algeria
Salah Refrafi: Department of Civil Engineering, Faculty of Sciences & Technology,
University Abbes Laghrour, Khenchela 40000, Algeria
Messaoud Bazzouzi: Department of Civil Engineering, Faculty of Sciences & Technology,
University Abbes Laghrour, Khenchela 40000, Algeria;
Civil Engineering Research Laboratory LRGC, Biskra University, 07000 Biskra, Algeria
Nabil Himeur: Department of Mechanical Engineering, Faculty of Sciences & Technology,
University Abbes Laghrour, Khenchela 40000, Algeria;
Laboratory of Engineering and Sciences of Advanced Materials (ISMA),
Abbes Laghrour University Khenchela, 40004, Algeria
Abstract
A sea-skimming unmanned aerial vehicle (UAV) is a specialized type of aircraft capable of performing
tasks at low altitudes above sea level. However, under extreme sea conditions, wave disturbances introduce
significant errors in measuring the relative distance between the UAV and the sea surface, which complicates the
control system and degrades flight performance. While existing research primarily relies on filtering or adaptive
control methods, their effectiveness in handling non-Gaussian disturbances remains limited. In this paper, a
mathematical model for the altitude and pitch motion of a sea-skimming UAV is established, taking into account
external disturbances caused by sea wave height. A control method integrating Backstepping theory with a nonlinear
disturbance observer (NDO) is designed to ensure system stability. The key innovation of this work lies in using the
NDO to estimate and compensate for aggregated disturbances, thereby enabling the Backstepping controller to
achieve exponential stability without a parameter adaptation process. Furthermore, a quasi-adaptive coefficient
function is incorporated into the NDO to adjust its gains in real time, improving estimation performance. The stability
of the proposed method is rigorously proven using Lyapunov theory. Simulation results demonstrate the effectiveness
of the NDO-based Backstepping control scheme, showing that it maintains a tracking accuracy of 98.52% even
under severe level 7 sea condition.
Address
Yunpeng Ji, Maria S. Selezneva: Faculty of automatic systems, Bauman Moscow State Technical University, Moscow,
2nd Baumanskaya str., 5, p. 1, Russia
Abstract
If hot bonding of the composite patch to the cracked plate leads to an improvement in the adhesion
energy between these two protagonists, it is a source of residual stresses in the plate, the adhesive and the patch near
their interfaces. Using FEM, this study aims to improve the performance of hot plate-patch joining and patch-crack
interactions by optimizing the patch shape. Thus, all the patch shapes developed in this study arise from an initially
rectangular shape. This results in six patch shapes: elliptical, orthogonal, star, H, double arrow and butterfly. This
optimization is analyzed in terms of improvement in both the fracture energy gain of the plate (stabilization of the SIF
with the evolution of the crack size K), the mechanical energy gain of the adhesive (reduction of the risk of rupture
of the adhesive by a drop in the level of shear stresses in the adhesive t) and of the mass gain of the patch m
(reduction of the risk of peeling and delamination and of debonding by an improvement of the aerodynamic
resistance of the patch). These three gains, K, t, m, developed for the first time in this study, constitute
characteristic criteria for the performance of composite patch repair. This is where the originality of this work lies.
This study highlights that improving the fracture energy gain alone is not a sufficient condition for the effectiveness of
hot repair. Thus, the simultaneous satisfaction of these three criteria is a necessary condition for the durability and
performance of the repair. This therefore constitutes the originality of this study which lies in the development of
these criteria. It appears from this study that the repair using an optimized double arrow-shaped patch leads to the
satisfaction of these criteria. This shape simultaneously ensures stabilization of the three components of the repair: the
plate by stabilizing the crack, the adhesive by reducing shear stresses, the patch by reducing its mass. The risks of
damage (debonding, peeling, delamination) due to these stresses and the size and thickness of the patch are clearly
minimized. It also emerges from this study that, contrary to previous works, hot bondings of the patch to the cracked
plate doesn't in any way affect the performance of the hot repair using an optimized patch.
Key Words
adhesive; composite patch; crack; energy gain; hot adhesion; interaction; mass gain;
performance criteria; rigidity; shear; stress; wettability
Address
Imene Lariche, Mehadjia Bezzerrouki, Mohammed Amine Bellali,
Mohammed Baghdadi, Boualem Serier: LMPM Laboratory, Djillali Liabes University, Sidi Bel Abbes, Algeria BP 89,
Cité Ben M
Abstract
This study investigates the thermo-mechanical behavior of cracked and porous Al-12Si/Al2O3 metalceramic
composites under varying thermal and mechanical conditions. A predicted model is developed to analyze
stress distribution, Young's modulus, and Poisson's ratio while incorporating the effects of porosity and ceramic
content. The results reveal that higher porosity weakens stress transfer and reduces stiffness, while increased ceramic
content enhances rigidity but also intensifies stress localization. Young' s modulus decreases significantly with
temperature and porosity. Poisson's ratio decreases with rising temperature, confirming reduced lateral deformation
resistance in more porous structures. The proposed model is validated against the Equivalent Constraint Model
(ECM), showing strong agreement in stiffness degradation trends. This study extends previous research by
integrating Knudsen's model into stress distribution analysis, providing a novel approach to quantify porosity effects
in thermo-mechanical behavior. The findings contribute to optimizing metal-ceramic composites for hightemperature
applications in aerospace and automotive industries, ensuring enhanced thermal and mechanical stability.
Key Words
meta/ceramic; porosity; stress distribution; thermal stress; young's modulus
Address
Billel Boukert, Mohamed Khodjet Kesba, A. Benkhedda: Aeronautical Sciences Laboratory, Institute of Aeronautics and Space Studies, University of Blida 1, BP 270
Route de Soumaa, Blida 09000, Algeria
E.A. Adda bedia: Materials and Hydrology Laboratory, University of Sidi Bel Abbes, Algeria
open access