Lambert C.A. Van Breemen

• Dr.ir.
• Professor (Assistant) at Eindhoven University of Technology

It is demonstrated that a large number of solid polymers (PMMA, PLLA, iPP, PS) display a pronounced change in kinetics (strain-rate and temperature dependence) after yield. The phenomenon finds its origin in the fact that, in specific ranges of temperature and strain rate, two different molecular processes may contribute to the yield stress. Becaus...

The one-mode EGP (Eindhoven glassy polymer) model captures the plastic flow at yield and post-yield quantitatively, but behaves poor in the non-linear viscoelastic pre-yield region. Since a proper description here is important in cases of complex loading and unloading situations, such as e.g. in indentation and scratching, an extension to non-linea...

Wear j o u r n a l h o m e p a g e : w w w . e l s e v i e r . c o m / l o c a t e / w e a r a b s t r a c t Generally it is understood that friction is additively decomposed into an adhesion-and a deformation-related component, suggesting independence. Experimentally these components cannot be separated and only by combining experiments with simul...

Upon their cooling and solidification, significant thermal residual stresses can develop in short-fiber reinforced thermoplastics due to the mismatch in coefficient of thermal expansion between fiber and matrix. In this study we set out to investigate this effect numerically. The build-up of thermal residual stresses is modeled by expanding a well-...

In this study, we demonstrate that the strength of a short‐fiber reinforced polymer as measured in uniaxial tension is not a good indicator for its strength under multiaxial loading conditions. To illustrate this fact, the influence of physical aging on the strength of a 20 wt% short‐fiber reinforced polycarbonate is studied for a uniaxial and biax...

An out-of-equilibrium simulation method for simulating the time evolution of glassy systems (or any other systems that can be described by hopping dynamics over a network of discrete states) is...

Fiber-reinforced polymer composites are largely employed for their improved strength with respect to unfilled matrices. Considering semi-crystalline materials under relevant processing conditions, the applied pressure and flow induce shear stresses at the fiber–polymer interface. These stresses may strongly enhance the nucleation ability of the fib...

The effects of temperature, pressure, and imposed strain on the structural transition pathways of glassy atactic polystyrene (aPS) are studied for a wide range of conditions. By employing an atomistic description of the system, we systematically explore its free energy landscape, emphasizing connections between local free energy minima. A triplet o...

Investigating and understanding the intrinsic material properties of biogenic materials, which have evolved over millions of years into admirable structures with difficult to mimic hierarchical levels, holds the potential of replacing trial-and-error-based materials optimization in our efforts to make synthetic materials of similarly advanced compl...

Determination of mechanical properties of (silica) thin films is important for the development of new applications. However, a versatile approach for small‐scale sample fabrication and in situ mechanical testing of these materials is currently lacking which can overcome the existing difficulties in conventional testing approaches. Here, it is shown...

The microstructure of products manufactured by selective laser sintering (SLS) is known to be highly dependent on various process and material parameters. The latter thus also affect the final part properties. While most work has focused on ex-situ characterization of the printed parts, little is known about the time-dependent microstructure develo...

Biocomposite structures are difficult to characterize by bulk approaches due to their morphological complexity and compositional heterogeneity. Therefore, a versatile method is required to assess, for example, the mechanical properties of geometrically simple parts of biocomposites at the relevant length scales. Here, it is demonstrated how a combi...

In this work we describe the production of spherical polymer particles from thermoplastic polymers. A simple method is developed to transform rough powders into spherical particles. The polymer particles are molten in heated oil whereafter interfacial tension driven reduction of curvature and shape retraction induce a transformation to the equilibr...

Transition pathways on the energy landscape of atactic polystyrene (aPS) glassy specimens are probed below its glass-transition temperature. Each of these transitions is considered an elementary structural relaxation event, whose corresponding rate constant is calculated by applying multidimensional transition-state theory. Initially, a wide spectr...

The relevant parts of the microstructure participating in the plastic deformation of glassy polystyrene are identified. This is achieved by performing quasi‐static deformation simulations of an atomistic representation of polystyrene, within a thermodynamic framework, under experimentally realistic boundary conditions (controlled compressive strain...

The mechanical properties and network structure of photocurable polymers are strongly dependent on processing conditions. Here it is reported that highly crosslinked acrylate systems undergo unexpected additional post‐curing during DMTA measurements, resulting in an increase in glass‐transition temperature (Tg). A detailed study of the conditions u...

Accurate estimation of mechanical properties of the different atherosclerotic plaque constituents is important in assessing plaque rupture risk. The aim of this study was to develop an experimental set-up to assess material properties of vascular tissue, while applying physiological loading and being able to capture heterogeneity. To do so, a ring-...

Photopolymerization of (meth)acrylates into highly crosslinked networks is in general accompanied by volumetric shrinkage, often leading to premature material failure. In this work, thermoreversible Diels–Alder groups are investigated to explore their effect on material lifetime. A difunctional acrylic monomer containing Diels–Alder moieties is syn...

In the area of polymer crystallization, the most widely used techniques to quantify structure, morphology and molecular orientation are fundamentally based on light or X‐ray scattering and absorption. In particular, synchrotron X‐rays are used for detailed studies on the semicrystalline structure in polymeric materials. The technical requirements f...

The effect of plastic deformation on the molecular dynamics of atactic polystyrene (a-PS) was studied by broadband dielectric relaxation spectroscopy (BDRS), Fourier-transform infrared spectroscopy (FTIR) and above its glass-transition temperature, resulting in thermal rejuvenation. Cold rolling revealed, in addition to the known a- and g (I)-relax...

The response of uniaxial and biaxial anisotropic polypropylene is discussed. A 3D elasto‐viscoplastic constitutive model is developed to account for material anisotropy. The famous Hill’s anisotropic yield criterion is combined with the Eyring relation and implemented in a finite element framework to model the response of the polymer during uniaxia...

Employing mechanofluorophores in polymer fractography to obtain new information on force-induced events when analyzed by confocal laser scanning microscopy.

We present a unique laser sintering setup that allows real time studies of the structural evolution during laser sintering of polymer particles. The device incorporates the main features of classical selective laser sintering machines for 3D printing of polymers and at the same time allows in situ visualization of the sintering dynamics with optica...

In this study, the effect of different process conditions on the material properties of a single UV-cured layer of methacrylate resin, typically used in the stereolithography (SLA) process, is assessed. This simplified approach of the SLA process gives the opportunity to study the link between process conditions and mechanical properties without co...

A rigorous thermodynamic framework is developed for performing free energy calculations of polymer glasses described by classical molecular forcefields. The proper free energy connected to all combinations of imposed external conditions (strain, stress) is derived from a well defined Helmholtz energy calculated from the detailed atomistic configura...

During the lifetime of polycarbonate surfaces, which for example are used as helmets or protective eye visors, friction and abrasive wear may result from scratching or sliding cycles. Previous research showed that it is essential to understand the intrinsic mechanical response of the polymer in order to further investigate its frictional and wear r...

The local and cooperative dynamics of atactic PS (a‐PS) were studied by broadband dielectric relaxation spectroscopy (BDRS) and attenuated total reflectance Fourier transform infrared spectroscopy (ATR‐FTIR). The a‐PS has been subjected to thermal rejuvenation and subsequent quenching, short‐term aging (6 weeks), and long‐term aging (1 year) at amb...

The determination of rheological and mechanical material properties becomes a challenge when the availability of material is limited to a few (milli)grams. This miniaturized testing is hampered by the contradicting requirements of small sample sizes (and thus surface areas) and sufficiently large generated torques and forces. In this paper we provi...

The objective of this work is to investigate the effect of the molecular mobility and resin formulation of UV‐curable acrylate systems on conversion and ultimate mechanical properties. Thin single‐layer films are produced from a series of nine mixtures of bisphenol A ethoxylate diacrylate, having different molecular weights (BisDAn = 2, BisDAn = 4,...

Trajectories of a long‐chain atactic polystyrene system, obtained from long Molecular Dynamics simulations in the glassy state, are mapped onto a time series of inherent structures of the potential energy landscape. The topology of the network of states formed is analyzed by employing graph‐theoretical concepts. It is found that the network of the...

Isotactic polypropylene (iPP) is a low cost semi-crystalline polymer that is easy to process, has a wide variety in properties and is, therefore, used in many applications. Many of these applications require enhanced wear-resistance to prolong the lifetime of the product. Essential is to first investigate the intrinsic response of the material in o...

We present a unique laser sintering setup that allows real time studies of the structural evolution during laser sintering of polymer particles. The device incorporates the main features of classical selective laser sintering machines for 3D printing of polymers and at the same time allows in situ visualization of the sintering dynamics with optica...

The ageing kinetics of amorphous atactic (a-PS), isotactic (i-PS), and syndiotactic (s-PS) polystyrene were studied by means of flash-differential scanning calorimetry. The specimens were aged for up to 2 h at six different ageing temperatures: the optimum ageing temperature, that is, the temperature at which the enthalpy overshoot at the glass tra...

Over the last two decades the study of friction has been an important topic in polymer tribology. The obtained knowledge about friction phenomena enables to take the next step towards understanding wear in polymers. When increasing the amount of local deformation in sliding friction experiments, the onset of failure is obtained, i.e. periodic crack...

Single-asperity scratching is used as a simplified contact problem to investigate the deformation due to two materials touching each other. Coupling the intrinsic polymer characteristics to the scratch response for blends of polystyrene (PS) and poly(2,6-dimethyl-1,4-phenylene oxide) (PPO) with varying composition is the main challenge of this stud...

In this study, the aging‐induced embrittlement of three polymer glasses is investigated using a previously developed hybrid experimental–numerical method. The evolution of yield stress of unnotched tensile bars upon aging is coupled to the evolution of embrittlement of notched tensile bars using a numerical model combined with a critical hydrostati...

Merging of particle pairs during selective laser sintering (SLS) of polymers is vital in defining the final part properties. Depending on the sintering conditions, polymers can undergo full or partial sintering whereby incomplete sintering results in poor mechanical properties. At present, the underlying mechanisms and related conditions leading to...

Epoxy resins represent an important class of thermosetting polymers that are extensively used in demanding applications like in scratch resistant coatings. Usually fillers, either hard (inorganic) or soft (rubbery), are added. Here we test hard and soft particle-filled epoxy systems in single asperity sliding friction experiments, and analyze the r...

This study presents the mechanical characterization of UV-curing acrylate systems. UV-curable polymers are commonly used in the stereolithography (SLA) technique to build multi-layered objects. Typically, the mechanical properties of the 3D-printed product are affected by the intrinsic material heterogeneity along the sample thickness. To understan...

Nowadays, in many applications metal parts are replaced by light-weight polymer products. As a result of the processing history, these polymer fabricates are, more often than not, anisotropic, leading to a direction dependent mechanical performance. Recently we showed the frictional response of isotactic polypropylene is improved by pre-stretching...

The present study describes the methodology to produce micron-sized disks from polymers which are available in small quantities i.e. 10 mg and to characterize them rheologically and mechanically. Relevant information to optimise processing conditions is extracted from the rheological characterization. The intrinsic mechanical behaviour is determine...

Polymers are increasingly used in applications where relative moving parts are in contact. The dissipation of energy due to friction, i.e. heat production, reduces a product's lifetime significantly. Since in processing often an extrusion or injection moulding step is used in product formation, the induced anisotropic microstructure leads to a spat...

Soft-solid foods show a progressive transition from a viscoelastic solid state to a flowing fluid state when subjected to a large load. The engineering properties and sensory texture of soft-solid foods depend strongly on the rheological properties that characterize this fluidization. In this paper we use Large Amplitude Oscillatory Shear (LAOS) rh...

A three-dimensional Representative Volume Element is used to analyze the local heterogeneous stress and strain distributions, and the onset to failure, in a standard epoxy system filled with sub-micron sized hard and soft particles. Computations are compared with experiments performed in lubricated compression tests that reveal the intrinsic materi...

Polymer composites used as protective coatings are important, tribology-critical applications. In this study, hard or soft particle-filled model systems with a polycarbonate matrix are tested in single asperity sliding friction tests against diamond tips. A numerical approach developed to simulate scratching on unfilled polycarbonate was adapted by...

Arrays of microneedles (MNAs) are integrated in an out-of-plane fashion with a base plate and can serve as patches for the release of drugs and vaccines. We used soft-lithography and micromolding to manufacture ceramic nanoporous (np)MNAs. Failure modes of ceramic npMNAs are as yet poorly understood and the question remained: is our npMNA platform...

Since polymers play an increasingly important role in both structural and tribological applications, understanding their intrinsic mechanical response is key. Therefore in the last few decades much effort has been devoted into the development of constitutive models that capture the polymers' intrinsic mechanical response quantitatively. An example...

A novel methodology is presented for pre-conditioning a polymer-coated steel used in food and beverage packaging. Mechanical rejuvenation of the coating via rolling is studied in order to prevent interface damage in subsequent forming operations. The simulations reveal that the thermodynamic state of the polymer coating after rolling depends on the...

We have studied the formation of nanoparticles in lead sulfide (PbS)-doped borosilicate glass subjected to a two-step nucleation and growth heat treatment using in situ small-angle X-ray scattering (SAXS). The microstructure produced was subsequently characterized using X-ray powder diffraction (XRD) and transmission electron microscopy (TEM). Whil...

The response to deformation of a detailed computer model of glassy atactic polystyrene, represented as a collection of basins on its potential energy landscape, has been investigated. The volumetric behaviour of the polymer is calculated via ‘brute force’ molecular dynamics quenching simulations. Results are compared with corresponding estimates ob...

Based on the concept of localized shear transformation zones (STZ), a thermodynamically consistent model for the viscoplastic deformation of amorphous solids is developed. The approach consists of a dynamic description of macroscopic viscoplasticity that is enriched by the evolution of number density and internal structure of the STZ for detailing...

A direct correlation is found between the time evolution of the yield stress in unnotched tensile bars and that of the impact energy measured using notched tensile bars. In both cases a master curve can be constructed with an Arrhenius type of shift function, using the same activation energy. Combining these experimental findings with numerical sim...

The lack of understanding of the mechanical behavior of the human skin layers makes the development of drug delivery using microneedles or microjets a challenging task. In particular, the key mechanical properties of the epidermis composed of stratum corneum and viable epidermis should be better understood. Micro-indentation experiments were applie...

The influence of the thermal history experienced during injection molding on the mechanical properties of polycarbonate is investigated. Distributions of the yield stress as they result from inhomogeneous cooling during processing, predicted by a previously developed modeling approach, are validated and are in good agreement with experiment. Predic...

The outer skin layers are important drug and vaccine delivery targets in the treatment of diseases. These skin layers possess some important characteristics making them favorable sites for pain-free delivery with minimal damage: a rich population of immunologically sensitive cells as well as the lack of blood vessels and sensory nerve endings [1]....

A previously developed model which predicts the yield stress of a polymer glass directly from processing conditions is applied to a system of miscible polymers. The selected system consists of a blend of polycarbonate with polyester and three blend compositions of increasing weight percentages polyester are investigated with respect to their aging...

Flat-tip micro-indentation tests were performed on quenched and annealed polymer glasses at various loading speeds. The results were analyzed using an elasto-viscoplastic constitutive model that captures the intrinsic deformation characteristics of a polymer glass: a strain-rate dependent yield stress, strain softening and strain hardening. The adv...

There are several techniques to probe local mechanical properties of polymer systems. Two frequently used techniques are indentation and scratching, also known as sliding friction. The first is used to determine material parameters such as Young's modulus and yield strength, the later to resolve issues concerning friction and wear properties. Both...

Time-to-failure of polymers, and the actual failure mode, are influenced by stress, temperature, processing history, and molecular weight. We show that long-term ductile failure under constant load is governed by the same process as short term ductile failure at constant rate of deformation. Failure proves to originate from the polymer's intrinsic...

This study deals with the influence of processing induced crystalline orientation on the macroscopic deformation and failure behavior of thin samples of polyethylene and polypropylene. Distribution and structure of flow-induced orientations were characterized by optical microscopy, X-ray diffraction techniques, and transmission electron microscopy....

The stacked lamellar morphology commonly found in extruded semicrystalline materials has a strong influence on the flow direction, with respect to the loading direction, and on the stability and localization phenomena in tensile experiments. A multiscale numerical model was used to simulate the effect on the macroscopic behavior of a stacked lamell...

Our recent work on extracting mechanical properties of polymers from indentation experiments shows that linear viscoelastic behavior, post-yield and crazing properties, and size effects can be characterized using a combined experimental-numerical approach. More research is needed in the field of full constitutive parameter extraction, thin film pro...

In this study an attempt is made to describe the thermorheologically complex deformation behaviour of the glassy polymer PMMA and semi-crystalline polymer iPP, by using a constitutive modelling approach [1]. For both polymers, it is shown that this approach successfully captures the thermorheologically complex behaviour of PMMA and iPP. Moreover, t...