A unified approach to Fierz identities

We summarize a unified and computationally efficient treatment of Fierz identities for form-valued pinor bilinears in various dimensions and signatures, using concepts and techniques borrowed from a certain approach to spinors known as geometric algebra. Our formulation displays the real, complex and quaternionic structures in a conceptually clear manner, which is moreover amenable to implementation in various symbolic computation systems.Comment: 6 pages, 5 tables, proceedings for TIM-12 Conference of Physic

Geometric algebra techniques in flux compactifications

We study `constrained generalized Killing (s)pinors', which characterize supersymmetric flux compactifications of supergravity theories. Using geometric algebra techniques, we give conceptually clear and computationally effective methods for translating supersymmetry conditions into differential and algebraic constraints on collections of differential forms. In particular, we give a synthetic description of Fierz identities, which are an important ingredient of such problems. As an application, we show how our approach can be used to efficiently recover results pertaining to N=1 compactifications of M-theory on eight-manifolds.Comment: 70 page

Comparative study between 2D and 3D FEM techniques in single bolt, single lap, composite bolted joints for space structures

Two-dimensional and three-dimensional finite element models have been developed to study the effects of bolt-hole clearance on the mechanical behavior of bolted composites (graphite/epoxy) joints in space structures. The type of the studied joint was single bolt, single lap, and the geometry is a standard type for these kind of composite joints space structures. In this study, two approaches, 2D (linear analysis) and 3D (nonlinear analysis) were developed and the results were compared to numerical and experiment results from literature. The contact between the parts affecting the accuracy and efficiency of the models is detailed. The model’s capability to predict the three-dimensional effects such as secondary bending and through-thickness variations of the stress and stain tensor fields is presented

Numerical analysis for the influence of the geometrical and mechanical parameters on the stiffness and strength of the composite bolted joints

The paper deals with the influence of the geometric (joint clearance) and mechanical parameters (bolt preload, axial force applied to the joint) on the stiffness and strength of the single-bolt, single-shear laminated composite joints using epoxy resin and carbon fibers reinforcement. In the first part of the paper, the finite element model is presented, using three-dimensional elements for studding the influence of the geometric and mechanical parameters on the stiffness of the joint. In the second part, the microscopic failure of the constituent layers using the Hashin failure criterion for composite materials is presented, as well as the influence of the studied parameters on the occurrence of the first lamina failure and the progressive failure phenomenon from the microscopic to the macroscopic level of the joint

Thermal Effects on Single - Lap, Single - Bolt, Hybrid Metal – Composite Joint Stiffness

three-dimensional finite element model has been developed to study the temperature effects on stiffness in linear-elastic range of the bolted metal-composite joints. In this study a quasi - symmetric lay - up for CFRP / vinyl ester epoxy laminate is used in conjunction with aluminum alloy (AA 7075 T6), having different thermal expansion coefficients. This generates an uneven load - deformation characteristics and three - dimensional stress field around the hole in single - lap single - bolt joints. The finite element model (FEM) was developed in commercial software PATRAN and the analysis including geometric and full nonlinearity frictional based contact has been performed using NASTRAN SOL 400 solver. The numerical model was calibrated using comparisons of the experimental measurements for surface strains and axial stiffness. The ability of the model to capture the three - dimensional effects such as secondary bending and through - thickness variation of stresses and strains in the presence of temperature variations is highlighted. The numerical and experimental results concluded that the thermal expansion material properties have a strong effect on the stiffness and linear behavior of the single - lap, single - bolt hybrid metal - composite joints

Temperature Effects on Damage Mechanisms of Hybrid Metal – Composite Bolted Joints Using SHM Testing Method

This paper presents the quasi-static thermo-mechanical loading effects on the progressive damage mechanisms and failure modes of the single-bolt, single-shear, hybrid metal-composite, bolted joints in aerospace applications. A three-dimensional finite element method (FEM) technique was used to model the countersunk head bolted joint in details, including geometric and frictional based contact full nonlinearities and using commercial software PATRAN as pre/post-processor. The progressive damage analysis (PDA) in laminated (CFRP/ vinyl ester epoxy) composite material including nonlinear shear behavior, Hashin-type failure criteria and strain-based continuous degradation rules for different values of temperatures was made using SOL 400 NASTRAN solver. In order to validate the numerical results and close investigation of the fracture mechanisms for metal-composite bolted joints by determining ultimate failure loads, experiments were conducted in temperature controlled chamber using SHM (Structural Health Monitoring) technique. The results show that the thermal effects are not negligible on failure mechanism in hybrid aluminum-CFRP bolted joints having strong different thermal expansion coefficients. The complex 3D FEM model using advanced linear continuum solid-shell elements proved computational efficiency and ability to accurately predict the various failure modes as bearing and shear-shear out, including the temperature effects on the failure propagation and damage mechanism of hybrid metal-composite bolted joints

Lunar Rickshaw – A non-Motorized Vehicle Designed for Exploration and Rescue Missions on the Moon’s South Pole

We have designed a simple, lightweight vehicle concept—a Lunar Rickshaw (LR)—engineered to rapidly and safely transport an incapacitated astronaut from a remote location to the Lunar Module (LM). In addition to its primary function for emergency evacuation, the Lunar Rickshaw can also serve as a mobile platform for carrying essential tools during extravehicular activities (EVAs). Key features include a rapid fold/unfold mechanism for quick deployment and stowage, a lightweight design that ensures ease of handling even in bulky spacesuits, and robust encapsulation to prevent lunar dust from affecting moving parts. Additionally, the design incorporates redundant fixing components so that if one fails, another seamlessly assumes the load, ensuring continuous, reliable operation in the harsh lunar environment. Another key aspect of the design is its widened wheel track, which enhances safety, balance, and stability during operation. Additionally, the pulling shaft is initially stored in a folded position for compact stowage. When deployed, it is unfolded and securely locked to the frame using a Lock-and-Walk Mechanism (LWM), ensuring structural rigidity, integrity, and efficient load distribution

Thermal Influence on the Stiffness of Hybrid Metal-Composite Countersunk Bolted Joints

This paper presents the effects of temperature on the axial stiffness of a hybrid metal-composite countersunk bolted joint designed for the bearing failure mode. A detailed 3D finite element model incorporating geometric, material and friction-based full contact nonlinearities is developed to numerically investigate the temperature effects on joint stiffness. In order to validate the temperature effects, experiments were conducted using an Instron testing machine coupled to a temperature controlled chamber. The results showed that the temperature effects on axial joint stiffness were quite accurately predicted by the 3D finite element model, denoting a reduction in the stiffness of the axial joint with an increase in temperature for hybrid metal-composite countersunk bolted joints.</jats:p

The Influence of Temperature on the Strength of Hybrid Metal-Composite Multi-Bolts Joints

This paper presents the temperature influence on the strength of the hybrid metal-composite multi-bolted joints. A detailed 3D finite element model, incorporating all possible nonlinearities as large deformations, in plane nonlinear shear deformations, elastic properties degradation of the composite material and friction-based full contact, is developed to anticipate the temperature changing effects on the progressive damage analysis (PDA) at lamina level and failure modes of metal-composite multi-bolted joints. The PDA material model accounts for lamina nonlinear shear deformation, Hashin-type failure criteria and strain-based continuum degradation rules being developed using the UMAT user subroutine in Nastran commercial software. In order to validate the temperature effects on the failure modes of the joint with protruding and countersunk bolts, experiments were conducted using the SHM (Structural Health Monitoring) technique in the temperature controlled chamber. The results showed that the temperature effects on damage initiation and failure modes have to be taken into account in the design process in order to fructify the high specific strength of the composites. Experimental results were quite accurately predicted by the PDA material model, which proved to be computational efficient and can predict failure propagation and damage mechanism in hybrid metal-composite multi-bolted joints.</jats:p

Static and Dynamic Design Methods for Hybrid Bolted Joints in a Satellite Structure

A detailed analytical design for hybrid (metal-composite) bolted joints in static and dynamic (random vibrations) analysis is presented in this paper. Due to the fact that a space structure must be lighter and stiffened, the joints design represents an important aspect in the overall mass-stiffness optimization process of the structure. The hybrid joint studied represents the attachment between a real space thruster bracket structure made from aluminum alloy and a composite spacecraft platform subjected to quasi-static and dynamic loads. These computing techniques, originally designed for metal joints, were translated to hybrid metal-composite joints using the finite element method (FEM). As a result, using the FEM technique, the design methods proposed have validated the ability to incorporate and describe in detail the effects of important phenomena such as clamping, friction, clearance and secondary bending of the joint, which are complex three-dimensional phenomena of major importance in the design process of a hybrid joint