Standard Compression-After-Impact test devices show a weakening effect on thin-walled specimens due to a free panel edge that is required for compression. As a result, thin-walled undamaged samples ...do not break in the free measuring area but near the free edge and along the supports. They also show a strength reduction due to the free edge which can become potentially relevant for very weakly damaged panels. In order to reduce the free edge influence on the measured strength, a modified Compression-After-Impact test device has been developed. In an experimental investigation with carbon fiber reinforced plastics, the modified device is compared with a standard device. It is shown that thin-walled undamaged specimens investigated with the modified device now mainly break within the free measuring area and no longer at the free edge and along the bearings as it is the case for standard test devices. The modified device does not cause a free edge weakening effect in comparison to standard devices. The modified device is therefore more suitable for determining the compression strengths of undamaged thin-walled composite plates.
Thin-walled fibre reinforced composites like carbon fibre reinforced plastics are very susceptible to strength reductions due to low-velocity impact damages. In aerospace engineering, the dominating ...failure mechanisms of impact damaged composite structures are usually investigated based on the compression after impact (CAI) test procedure. This enables the determination of the influence of impact damages on the static residual compressive strength. CAI testing procedures are typically applicable to composite plates with thicknesses larger than 3–4 mm. If thinner panels are used, they typically fail near one of the loaded edges of the CAI device, in particular the area of the free edge (which is needed for compressing the panel) and not within the free measuring area. As a consequence, the investigated samples cannot be used as valid tests for the evaluation of the residual strength in CAI testing. In order to enable an investigation of the residual strength of thin-walled plates in CAI testing, a CAI testing device is developed based on an available CAI fixture and a standardized one. For comparability reasons, this new device exhibits the same dimensions as standardized fixtures. It shows a significant improvement with respect to standardized devices concerning the measurement of mechanical behaviour during CAI testing.
Abstract
In engineering sciences like mechanical or automotive engineering, pre-knowledge in mathematics is required to follow deeply specific engineering lectures. Mathematical skills are essential ...preconditions to successfully complete engineering lectures. It is necessary that these preconditions are identified for each individual student so that suitable learning opportunities can be provided according to the individual student needs. Within this paper an approach of competence-based learning in engineering mechanics is presented. This approach is assisted by an online learning environment that is adapted and extended by several features in order to enable a competence-oriented learning strategy. Computer-assisted tests are used for measuring mathematical pre-knowledge and pre-skills. Moreover, a mastery learning approach based on exercises is utilized in order to secure a certain skill level before students move forward to learn subsequent competencies. Test results influence the individual learning path by offering different learning elements to each student.
Geometric imperfections are induced in composite structures due to manufacturing and assembly processes as well as due to accidental impacts. These geometric imperfections have an influence on the ...strength of thin-walled composite structures when impact damage is present. Therefore, the influence of the geometric imperfection magnitude on the failure mechanisms of thin-walled laminates with initial internal damage patterns under Compression-After-Impact testing is investigated by creating a finite element model based on different experimental validations. These experiments are a set of tensile tests, low energy impact tests with a pendulum system to induce the internal damage patterns, ultrasonic scanning of the damaged samples to characterize the delaminated areas and, finally, a set of Compression-After-Impact tests combined with digital imaging correlation data using an ARAMIS 3D measuring system (Gom mbH, Braunschweig, Germany). Compression-After-Impact tests are carried out with a frame modified for thin-walled laminates enabling a more reliable measurement of thin laminates. All these data collected during the experiments and damage inspections are used to build up and validate the simulations with the Finite Element code Abaqus (Dassault Systèmes SA, Paris, France). Finally, potential interactions between global and local failure mechanisms in Compression-After-Impact testing are analyzed with different imperfection magnitudes and interface damage idealizations based on these models. The results show an increase of the failure strength with the initial imperfection magnitude.
Recently, CLPB deficiency has been shown to cause a genetic syndrome with cataracts, neutropenia, and 3-methylglutaconic aciduria. Surprisingly, the neurological presentation ranges from completely ...unaffected to patients with virtual absence of development. Muscular hypo- and hypertonia, movement disorder and progressive brain atrophy are frequently reported. We present the foetal, peri- and neonatal features of 31 patients, of which five are previously unreported, using a newly developed clinical severity scoring system rating the clinical, metabolic, imaging and other findings weighted by the age of onset. Our data are illustrated by foetal and neonatal videos. The patients were classified as having a mild (
n
= 4), moderate (
n
= 13) or severe (
n
= 14) disease phenotype. The most striking feature of the severe subtype was the neonatal absence of voluntary movements in combination with ventilator dependency and hyperexcitability. The foetal and neonatal presentation mirrored the course of disease with respect to survival (current median age 17.5 years in the mild group, median age of death 35 days in the severe group), severity and age of onset of all findings evaluated. CLPB deficiency should be considered in neonates with absence of voluntary movements, respiratory insufficiency and swallowing problems, especially if associated with 3-methylglutaconic aciduria, neutropenia and cataracts. Being an important differential diagnosis of hyperekplexia (exaggerated startle responses), we advise performing urinary organic acid analysis, blood cell counts and ophthalmological examination in these patients. The neonatal presentation of CLPB deficiency predicts the course of disease in later life, which is extremely important for counselling.
A displacement-based finite element for static and stability analyses of sandwich plates is formulated using a three-layer sandwich model. The face sheets are idealized as classical plate elements ...assuming the Kirchhoff—Love hypothesis. The core displacement field is derived using the solution of the underlying differential equations of the core in the through-thickness direction z and the assumed deflections of the face sheets as boundary conditions. The differential equations are determined based on a three-dimensional material law neglecting the in-plane core stiffnesses. This approach leads to in-plane core deformations uc and vc, which are cubic functions of z, and to an out-of-plane deflection wc, which is a quadratic function of z. Based on the interpolation functions, the linear and geometric stiffness matrix for static and stability problems are derived, whereas the geometric stiffness matrix is set up by considering geometric nonlinearities in the v. Kármán sense in the face sheets.
A finite element for the static and stability analysis of sandwich plates is formulated based on a three-layer sandwich model and its underlying differential equations. The Kirchhoff-Love hypothesis ...is assumed for the face sheets. The core is modelled by a three-dimensional material law neglecting the in-plane core stiffnesses. A stability analysis is performed on the basis of the geometric stiffness matrix considering the membrane prestresses of the face sheets.
Virtual Production Systems Schulz, Wolfgang; Bischof, Christian; Bobzin, Kirsten ...
Integrative Production Technology for High-Wage Countries,
2011, 20111217
Book Chapter
The use of simulation systems is of significant importance for companies in high-wage countries as the requirements of product- and process quality are generally higher than in low-wage countries due ...to conditions of the market. Since the implementation of simulation tools is not value-adding in the first place, the performance of virtual product development chain must therefore be continuously increased in terms of greater planning efficiency. Research in the field of virtual production systems therefore addresses the following issue.
The innate immune system is central for the maintenance of tissue homeostasis and quickly responds to local or systemic perturbations by pathogenic or sterile insults. This rapid response must be ...metabolically supported to allow cell migration and proliferation and to enable efficient production of cytokines and lipid mediators. This Review focuses on the role of mammalian target of rapamycin (mTOR) in controlling and shaping the effector responses of innate immune cells. mTOR reconfigures cellular metabolism and regulates translation, cytokine responses, antigen presentation, macrophage polarization and cell migration. The mTOR network emerges as an integrative rheostat that couples cellular activation to the environmental and intracellular nutritional status to dictate and optimize the inflammatory response. A detailed understanding of how mTOR metabolically coordinates effector responses by myeloid cells will provide important insights into immunity in health and disease.
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