Jānis Andersons

Jānis Andersons
University of Latvia | LU · Institute for Mechanics of Materials

Dr. sc. ing.

About

161
Publications
19,620
Reads
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3,233
Citations
Additional affiliations
January 2016 - present
University of Latvia
Position
  • Senior Researcher
July 2014 - present
Latvian State institute of Wood chemistry
Position
  • Engineer
September 1999 - October 1999

Publications

Publications (161)
Article
Full-text available
Citation: Vevere, L.; Yakushin, V.; Sture-Skela, B.; Andersons, J.; Cabulis, U. Cryogenic Insulation-Towards Environmentally Friendly Polyurethane Foams. Polymers 2024, 16, 2406. https://doi. Abstract: Cryogenics is the science and technology of very low temperatures, typically below 120 K. The most common applications are liquified natural gas car...
Article
Low-density closed-cell polyurethane (PU) foams are widely used in thermal insulation in diverse applications, therefore predicting their thermal aging has a distinct practical importance. Several approaches have been developed allowing forecasting the long-term changes of gas composition in foams, which manifest as the thermal aging. The accelerat...
Article
Low-density brittle foams, although not expected to carry mechanical loads, have to retain structural integrity during service in order to deliver the expected functional characteristics. The fracture toughness of low-density foams exhibits anisotropy when foam cells acquire anisometric shape due to, e.g., the presence of a preferential direction f...
Article
Full-text available
Thin-walled carbon fiber reinforced plastic (CFRP) shells are increasingly used in aerospace industry. Such shells are prone to the loss of stability under compressive loads. Furthermore, the instability onset of monocoque shells exhibits a pronounced imperfection sensitivity. The vibration correlation technique (VCT) is being developed as a nondes...
Article
Full-text available
The characteristics of rigid, nanoclay-filled, medium-density NEOpolyol-380 polyure-thane foams components can be estimated when two conditions are met: (1) the foam blocks are produced in a sealed mould; and (2) the mass of the reacting mixture is kept constant. It was shown that, with an increase in filler concentration, the total mass of the fil...
Data
Supplementary Materials to an article "Characteristics of Components and Density of Rigid Nanoclay-Filled Medium-Density Polyurethane Foams Produced in a Sealed Mould" Ilze Beverte, Ugis Cabulis, Janis Andersons, Mikelis Kirpluks, Vilis Skruls and Peteris Cabulis
Article
Full-text available
Citation: Beverte, I.; Cabulis, U.; Andersons, J.; Kirpluks, M.; Skruls, V.; Cabulis, P. Anisotropy and Mechanical Properties of Nanoclay Filled, Medium-Density Rigid Polyurethane Foams Produced in a Sealed Mold, from Renewable Resources. Polymers 2023, 15, 2582. Abstract: Medium-density rigid polyurethane (PU) foams are often produced in sealed mo...
Patent
Full-text available
„A detachable, reusable polypropylene mould for making Of cylindrical rigid polyurethane foams’ blocks” 1)Field of the invention The present invention relates to a detachable, reusable mold for making of cylindrical blocks of rigid polyurethane foams. 2)Summary The invention relates to a detachable, reusable mold for making of cylindrical blocks...
Article
Full-text available
Abstract: A shortage of research on the impact of atmospheric parameters on the measured dielectric permittivity values of rigid polyurethane (PU) foams was identified. Therefore, the impact of temperature, pressure, and relative humidity of air in the test room on the measured values of dielectric permittivity of rigid PU foams of different densit...
Article
Rigid low-density closed-cell polyurethane foams with different crosslink densities have been produced using biobased polyols derived from tall oil. Mechanical and dilatometric tests reveal that the transverse stiffness and tensile strength of the foams increased with growing crosslink density both at the room and cryogenic temperatures, while the...
Data
Supplementary materials (https:// www.mdpi.com/article/10.3390/polym14061154/s1) to the article Beverte, I.; Cabulis, U.; Andersons, J.; Kirpluks, M.; Skruls, V.; Cabulis, P. Light Microscopy of Medium-Density Rigid Polyurethane Foams Filled with Nanoclay. Polymers 2022, 14, 1154. https://doi.org/ 10.3390/polym14061154
Article
Full-text available
Practical applications and mathematical modelling of the physical and mechanical properties of medium-density rigid polyurethane foams require knowledge of their structure. It is necessary to determine structural characteristics without destroying the foams and measuring each element. A methodology is described for the use of light microscopy on en...
Article
Full-text available
Rigid low-density plastic foams subjected to mechanical loads typically exhibit a nonlinear deformation stage preceding failure. At moderate strains, when the geometrical nonlinearity is negligible, such foam response is predominantly caused by the nonlinearity of deformation of their principal structural elements—foam struts. Orientational averagi...
Article
Rigid low-density polyurethane (PU) foams containing bio-based components are being increasingly considered as a sustainable substitute for petrochemical resources-based foams for thermal insulation in ambient conditions. However, for applications involving high temperature gradients, the thermal expansivity of foams also has to be characterised. W...
Poster
Full-text available
Latvian Council of Science; project Nr. lzp-2020/2-0260 "Impact of the spatial alignment of anisometric nanoclay filler's particles on physical and mechanical properties of low-density rigid polyurethane foams" (Acronym: AnisoFillFoam) The aim of this research is characterisation of relocation and spatial alignment of the anisometric nanoclay fille...
Article
Low-density closed-cell polyurethane (PU) foams are applied as thermal insulation materials due to their low thermal conductivity imparted by that of the physical blowing agent (PBA) used in foam production. However, foam conductivity tends to gradually increase with time, primarily due to changes in the gas composition in foam cells brought about...
Article
Sustainable development of building industry implies increasing usage of green materials. With this aim and for the intended application as a structural thermal break material, rigid high-density polyurethane foams have been manufactured using polyols derived from renewable resources - tall oil fatty acids. Thermal conductivity, compressive strengt...
Article
Full-text available
Rigid low-density closed-cell polyurethane (PU) foams are widely used in both thermal insulation and structural applications. The sustainability of PU foam production can be increased by using bio-based components and fillers that ensure both enhanced mechanical properties and higher renewable material content. Such bio-based foams were produced us...
Article
Full-text available
Rigid low-density closed-cell polyurethane (PU) foams are used primarily as a thermal insulation material. The foams have to possess a sufficient strength and stiffness in order to ensure their mechanical integrity and dimensional stability in service. The mechanical characteristics of foams are enhanced by adding cellulose nanofibers to the polyol...
Conference Paper
Polyols from different sustainable resources have been widely studied as one of the raw materials for polyurethane (PUR) material production in recent years. The renewable materials have been proven as a viable alternative for petrochemical products from their properties perspective. This study describes the development of rigid PUR foam impact abs...
Article
Full-text available
A one-parameter lamina plasticity model is applied to predict the nonlinear deformation of an E-glass / epoxy cross-ply composite laminate under quasi-static uniaxial tensile loading at different angles to the material orthotropy axes. It is shown that the laminate theory yields accurate results within the plastic strain range covered in unidirecti...
Article
Full-text available
Nanocellulose in the form of whiskers and nanofibers has become a promising reinforcement material for polymer composites due to its high mechanical characteristics and sustainability. For optimization of composite properties, efficient means of characterization of the stress transfer between fibrous nanofiller and the polymer matrix are needed. In...
Article
In order to fully realize the efficiency of bast fibers or their yarns as reinforcement of polymer composites, they should be aligned. Tensile strength of such composites in the direction of reinforcement has been found to exhibit size effect commensurable with that of unidirectionally reinforced (UD) composites with inorganic fibers, necessitating...
Article
Due to the high deformability and energy dissipation capacity of polymer foams in compression, they are used in automotive applications to mitigate mechanical impacts. The mechanical response of the foams is strongly affected by their density. Phenomenological relations have been proposed to describe the effect of foam density on their stress-strai...
Article
Full-text available
Applicability of the vibration correlation technique (VCT) for nondestructive evaluation of the axial buckling load is considered. Thin-walled cylindrical shells with and without circular cutouts have been produced by adhesive overlap bonding from a sheet of aluminium alloy. Both mid-surface and bond-line imperfections of initial shell geometry hav...
Article
Full-text available
A structural model of a highly porous cellular plastic reinforced with short fibers is developed for calculating its linearly elastic characteristics. By means of orientationally averaging the stiffness tensors of structural elements, whose dimensions and properties also depend on their spatial orientation, relationships for the stiffness tensor of...
Chapter
Rigid closed-cell polyurethane (PUR) foams are used in diverse applications ranging from thermal insulation in buildings and appliances and cryogenic insulation in liquefied gas tankers and airspace vehicles to impact-mitigating components in the automotive industry. To alleviate environmental concerns and enhance the sustainability, polyols derive...
Article
Full-text available
Low-density foams have to possess a sufficient resistance to cracking in order to ensure the mechanical integrity of foam materials in service, even when not intended for load-bearing applications. In this study, mode I fracture toughness in the foam rise direction has been experimentally characterized for anisotropic rigid commercial polyurethane...
Article
Full-text available
In order to enhance the mechanical properties of polymer foams, fillers of different materials and sizes are being applied. Fibrous fillers shorter than the characteristic foam cell dimensions have the potential of efficient reinforcement, due to their high aspect ratio, without detrimentally interfering with foam structure. A theoretical model is...
Article
Full-text available
Carbon fiber-reinforced polymer (CFRP) is an advanced lightweight composite material with high strength and excellent resistance to corrosion and fatigue. Over the past decades, application of fiber-reinforced polymers has been spread from the aerospace to other branches of industry such as automobile and civil engineering. Unidirectional CFRP has...
Article
The cells of polymer foams are usually extended in the foam rise direction, causing a geometrical anisotropy, the degree of which, characterized by the cell aspect ratio R, depends on foam density and production method. Such elongated cell shape translates into anisotropy of the mechanical properties of foams. Rigid low-density closed-cell polyisoc...
Article
The paper deals with an indirect industry-friendly method for identification of the interfacial shear strength (IFSS) in a fully bio-based composite. The IFSS of flax fiber/starch acetate is evaluated by a modified Bowyer and Bader method based on an analysis of the stress¬-strain curve of a short-fiber-reinforced composite in tension. A shear lag...
Article
The interfacial shear strength (IFSS) between nickel-titanium (NiTi) shape memory alloy wires, characterized by a nonlinear stress-strain behavior, and epoxy matrix was determined by pull-out tests. Tests were carried out at several temperatures and levels of pre-strain in the wires, to evaluate the effects of embedded wire length and of crystallin...
Article
In order to elucidate the effect of stress concentration on the tensile strength of rigid polyurethane (PUR) foams, specimens with open circular holes and different ratios of hole diameter to specimen width were tested in tension. The reduction in the net-section strength of the specimens with a center hole ranged from 1 to 18% for neat foams and f...
Chapter
Ecological and economical considerations foster replacement of man-made fibers by natural renewable fibers in various industrial applications. Proper description of the scale effect of fiber strength is important for theoretical estimation of the load-carrying capacity of their products. Bast fibers of such plants as, e.g., flax, hemp, jute etc. ar...
Article
The effect of stress raisers in the form of a slit-like notch and an open circular hole on the tensile strength of a quasi-UD flax-fiber-reinforced composite is studied experimentally. A finite fracture mechanics approach is applied to determine the intralaminar fracture toughness of the composite and to predict the strength in the presence of stre...
Article
In an attempt to fully utilize the mechanical properties of bast fibers in polymer-matrix composites, unidirectional (UD) or quasi-UD flax-fiber-reinforced composites are being developed and characterized. Their response in tension is markedly nonlinear both in on- and off-axis loading. A semiempirical tensor-linear model is applied to describe suc...
Conference Paper
Full-text available
Confinement of concrete structural elements by fiber-reinforced polymer-matrix composite sheets is increasingly being used to strengthen or retrofit a structure. Along with carbon, glass, and basalt fiber reinforcement, natural fibers are being considered for such applications. Utilization of plantderived natural fibers as the reinforcement of poly...
Chapter
The objective of this chapter is to present experimental methods that are suitable for characterization of cellulose fibers. An overview of different techniques to obtain and analyze fiber strength distribution is presented. The differences of internal structure and mechanical behavior between natural and synthetic fibers, applicability and validit...
Article
The biomass represents an abundant, renewable, competitive and low cost resource that can play an alternative role to petrochemical resources. The central topic of the research activity reported is the use of rape seed oil (RO) as a raw material for the production of rigid polyisocyanurate foams (PIR). The content of the renewable resource-derived...
Article
Full-text available
Polyisocyanurate foams have been developed using a polyol system partially derived from rapeseed oil (RO). The effect of nanofillers with iso-dimensional geometry (zinc oxide), nanofibers (carbon nanotubes), and nanoplatelets (organically modified montmorillonite) on stiffness and strength of the foams has been studied. It was demonstrated that the...
Article
The growing usage of short-flax-fiber-reinforced polymer composites in such applications as automotive industry necessitates the prediction of their mechanical response up to and beyond the limit of elasticity. Due to the imperfect, mechanical interlocking-dominated adhesion of natural fibers to most polymers, both fiber debonding and matrix yieldi...
Article
The principal aim of the present research was to predict the strength of UD basalt fiber/epoxy matrix composites in tension along the reinforcement direction. Tension tests on single basalt fibers were performed to determine the functional form of their strength distribution and to evaluate the parameters of the distribution. Also, microbond tests...
Article
The application of hemp fibers as a reinforcement of composite materials necessitates the characterization of fiber strength scatter and the effect of fiber length on its strength. With this aim, elementary hemp fibers were tested in tension at two different gage lengths. Due to the similar morphology of hemp and flax fibers, the probabilistic stre...
Article
Full-text available
A method for calculating the elastic constants of high-porosity cellular materials is proposed on the assumption that their oriented structure can be considered as a linear transform of some random structure. A simplified procedure to take into account the effect of gas pressure in closed-cell anisotropic solids on their elastic constants is also s...
Article
Full-text available
Polyisocyanurate foams incorporating polyols derived from rapeseed oil are developed, with the polyol system comprising up to 80% of rapeseed oil esters. To enhance the mechanical characteristics and fire resistance of the foams, they are filled with three different types of organically modified clay (organoclay) in the range of loading from 1 to 5...
Conference Paper
Full-text available
The most common semi-rigid roadside barrier system uses a steel w-beam guardrail. Replacement of the steel by a thermoplastic polymer composite as the guardrail material is likely to bring both economic (e.g. utilization of recycled plastic) and functional benefits. With this aim, E-glass fiber/polyethylene composite material, produced by thermofor...
Conference Paper
Full-text available
Application of plant-derived natural fibers as the reinforcement of polymer-matrix composites is driven by economic and environmental reasons. In order to fully exploit the reinforcing effect of the fibers, they have to be aligned in the composite material. When using such UD composites in load-bearing applications, the dependence of strength on th...
Conference Paper
Full-text available
Low-density rigid polyisocyanurate (PIR) foams obtained from renewable resources (with the polyol system comprising up to 80% of rapeseed oil esters) have been produced and tested for strength and fracture toughness in a range of foam density of importance for practical applications. In order to enhance the mechanical characteristics of the foams,...
Conference Paper
Full-text available
Replacement of most common semi-rigid roadside barrier system, based on steel w-beam guardrail, by a thermoplastic polymer composite as the guardrail material is considered. With this aim, production technology of E-glass fiber/low density polyethylene composite by a continuous thermoforming process from glass fiber roving, glass-fiber fabric, and...
Article
Full-text available
Rigid low-density closed-cell polyisocyanurate (PIR) foams are used primarily as a thermal insulation material. Traditionally, they are manufactured from constituents produced by petrochemical industry. Introducing renewable materials in PIR formulation brings definite economical and environmental benefits. Fracture toughness of PIR foams obtained...
Article
An important factor affecting the mechanical characteristics of composite materials is the adhesion of constituents which can be characterized by the interfacial shear strength (IFSS). Most of the experimental methods for the evaluation of IFSS involve model single-fiber composites. By contrast, the method proposed by Bowyer and Bader is based on a...
Article
Full-text available
This paper is a review integrating, amending, and developing the approach applied in authors’ previous works devoted to the tensile and fatigue reliability analysis of unidirectional composite material considered as a series system the links of which are, in general case, complex parallel systems with redistribution of load after failure of some it...
Article
Full-text available
As a development of the model where only one weak microvolume (WMV) and only a pulsating cyclic loading are considered, in the current version of the model, we take into account the presence of several weak sites where fatigue damage can accumulate and a loading with an arbitrary (but positive) stress ratio. The Poisson process of initiation of WMV...
Conference Paper
Full-text available
With the commercial production of unidirectionally (UD) reinforced flax fiber prepregs, an opportunity to design composite lay-ups tailored for specific applications has arisen. For that, mechanical characteristics of a UD composite need to be known. With this aim, plain and notched UD flax/epoxy composites have been tested in on-and off-axis tensi...
Article
A method of interfacial shear strength evaluation, based on the length distribution of fibers pulled out from the tensile fracture surface of an oriented flax-reinforced composite, is applied to composites with vinyl ester and acrylated epoxidized soy oil resin matrices. Two approaches for characterizing the strength of fibers with modified Weibull...
Conference Paper
Polyurethane and polyisocyanurate foam materials are used in diverse applications including thermal insulation, furniture, packaging, automotive industry etc. In applications demanding specific mechanical characteristics, polymers are filled by fibers or particles before foaming to enhance the stiffness and strength of the foams. Using fillers with...
Article
Ecological and economical considerations foster replacement of man-made fibers by natural renewable fibers in various industrial applications. Bast fibers of such plants as, e.g., flax, hemp, jute etc., are particularly attractive as a reinforcement of polymer-matrix composites due to their high specific stiffness and strength in the axial directio...
Conference Paper
Full-text available
Reliability of a fiber-reinforced composite material in tension along fiber direction is governed by the strength distribution of the fibers and local load redistribution characteristics at broken fibers. Using flax fabric as the reinforcement introduces additional hierarchic level, that of fiber yarns. Such a composite material can be considered a...
Conference Paper
Full-text available
Adhesion of the constituents in fiber-reinforced polymers, frequently characterized by the interfacial shear strength (IFSS), is an important characteristic of the composite material determining to a large extent its strength and toughness. A number of experimental methods have been developed for evaluation of the IFSS. However, it has been argued...
Article
This paper is a review of the authors’ previous work devoted to the analysis of tensile strength of unidirectionally fiber-reinforced composite material, considered as a series of parallel systems with defects. Additionally, a specific model is studied based on an assumption that only failure of the damaged parts of a specimen can take place. A ver...
Article
Adhesion of flax fibers and polymer matrix as well as mutual bonding of elementary fibers in a technical fiber are among the principal factors governing the mechanical response of flax fiber-reinforced polymer–matrix composites. A method for evaluation of adhesion is proposed based on tension tests of impregnated fiber yarns, with subsequent charac...
Article
The competition between two common failure modes of a thin coating under in-plane compression, the surface wrinkling and the buckling-driven delamination, is studied to assess the critical strain when the mechanical instability may occur at given geometrical and material parameters. A buckling map is constructed based on results of a finite element...
Article
Full-text available
Natural-fiber-reinforced short-fiber composites are finding more applications lately, therefore there is a need for estimation of the mechanical properties of such composites based on the properties of the constituents. The fibers themselves also possess complicated internal structure, resulting in anisotropy of their properties. Taking into accoun...
Article
Full-text available
A model is presented for calculating the linear elastic constants of high-porosity cellular plastics by orientationally averaging the rigidity tensor of a structural element consisting of an air sheath and a load-carrying element in the form of a straight strut with a piecewise constant cross section. The load-carrying element can resist the axial...
Article
The development of UD natural fiber composites, considered for application as structural materials, necessitates evaluation of the scale effect of their strength. Alignment of the fibers in flax bast fiber composites can be achieved by employing textile reinforcement, such as yarns and fabrics. Cutting specimens for mechanical tests out of such tex...
Article
Unidirectional orientation of natural fibers in a polymer composite ensures the highest efficiency of reinforcement. Flax fiber reinforcement is discontinuous due to limited fiber length and heterogeneous due to the presence of elementary fibers and their bundles. In order to assess the upper limit of tensile strength of such slightly misoriented,...
Article
To exploit the potential of natural fibers as reinforcement of polymer matrix composites, aligned bast fiber composite materials are being produced and studied. Bast fiber reinforcement is discontinuous due to the limited length of natural fibers, which needs to be reflected in predictive models of mechanical properties of composites. The strength...
Article
Flax fibres possess high specific strength and stiffness, and thus are competitive in terms of mechanical properties with the traditional reinforcing fibres used in polymer-matrix composite materials. The mechanical properties of fibres have considerable variability that needs to be characterized and allowed for in the analysis of mechanical respon...
Conference Paper
Full-text available
Agrofibers, including bast fibers of flax, are increasingly applied as reinforcement of polymer-matrix composite materials due to environmental and ecological concerns. Unidirectional (UD) alignment of the fibers in a composite is preferable to fully exploit the mechanical properties of the natural fibers. Whereas an elementary rule of mixtures can...
Article
Elementary bast fibers, apart from acceptable specific mechanical properties, possess a marked variability in geometrical and damage characteristics, which affects their axial tensile strength. A strength distribution function is derived that allows for the effect of kink bands and the scatter of fiber diameter. The distribution function is validat...
Article
Fiber-reinforced polymer–matrix composites are known to exhibit loading rate- and time-dependent mechanical response. Their fatigue strength is determined by a complex interaction of damage processes governed by loading duration and cycle number. Apart from mechanistic approaches, a number of empirical models of various sophistication have been pro...
Article
Cross-ply laminate subjected to tensile loading provides a relatively well understood and widely used model system for studying progressive intralaminar cracking. The transverse ply cracking is an inherently stochastic process due to the random variability of local material properties of the plies. The variability affects both crack initiation and...
Article
Natural fibers of plant origin, used as reinforcement in polymer matrix composite materials, exhibit highly anisotropic elastic properties due to their complex internal structure. Mechanical properties can be evaluated not only by tests but also by mechanical models reflecting the principal morphological features of fibers. Such a FEM model is appl...
Article
Full-text available
Natural fibers of plant origin are finding non-traditional applications as reinforcement of composite materials. The mechanical properties of fibers exhibit considerable scatter, being affected by the natural variability in plant as well as the damage accumulated during processing. For bast fibers, the primary damage mode is kink bands – zones of m...
Article
The presence of stress concentrations at holes and notches is known to reduce the strength of composite materials. Due to complexity of the damage processes at a stress raiser in a composite, different modeling approaches have been developed, ranging from empirical point and average stress criteria to involved damage mechanics or cohesive zone-base...
Article
An analysis of the tensile strength of some fiber or fiber bundle specimens is presented. The specimens are modeled as chains of links consisting of longitudinal elements (LEs) with different cumulative distribution functions of strength, corresponding to the presence and absence of defects. Each link is considered as a system of parallel LEs a par...
Article
The influence of internal stress anisotropy resulting from anisotropic loading in a roll-to-roll (R2R) process, and polymer substrate anisotropy on the crack onset strain (COS) of thin oxide coatings was analyzed. Experimental data obtained for R2R processed films were compared with data obtained using an isotropic sheet-to-sheet (S2S) process with...
Article
Evaluation of interfacial toughness of sub-micron-thickness layers deposited on a ductile substrate is a challenging task which has motivated different experimental approaches. Fragmentation testing was used in the present study as a means of interface characterization of a silicon–nitride-coated polyimide substrate. During the test, after an initi...
Article
The criticality of rotor and stator contact in a large-size marine separator is studied by numerical modelling. Two plausible mechanisms leading to such contact, namely rolling of a ship in steady-state motion and a suddenly occurring unbalance in the rotor, are considered. It is found that contact due to sea motion may be tolerable, while sudden d...
Conference Paper
The present study concerns the evaluation of the interfacial adhesion properties of a SiNx coating on a polyimide substrate from the analysis of coating edge delamination during fragmentation test. The extent of the delamination was correlated to the width of a bright interference fringe observed under white light at fragment edges. A two-dimension...
Article
Evaluation of interfacial toughness of sub-micron-thickness layers deposited on a ductile substrate is a challenging task which has motivated different experimental approaches Fragmentation testing was used in the present study as a means of interface characterization of a silicon-nitride-coated polyimide substrate. During the test, after an initia...
Article
Flax fibers possess high specific strength and stiffness, and thus are competitive in terms of mechanical properties with traditional reinforcing fibers used in polymer-matrix composite materials. For environmental and economical benefit, it would be preferable to apply nontextile grade fibers in composites provided their mechanical characteristics...