Mechanical Characterization Methods Research Articles

Enhancing fiber/matrix interface adhesion in polymer composites: Mechanical characterization methods and progress in interface modification

The interface between the fiber and polymer matrix is a crucial region that plays a major role in the mechanical performance of fiber reinforced polymer composites (FRPCs) materials. The properties of this zone are recognized to have a significant influence on the fracture and failure of FRPCs. As a result, strong adhesion at the interface is required for effective stress transfer and load distribution within the composite material. In light of this, the aim of this work is to provide an up-to-date review of test methods for assessing fiber/matrix interface adhesion in FRPCs under static and dynamic loadings, along with advancements in interface modification techniques. At the outset, we give an overview of the different modification treatments used thus far, alongside interface testing methods, in order to optimize fiber/matrix compatibility, improve interfacial bonding and scrutinize their impact on interfacial adhesion properties. Particular attention is then focused on the description of the main mechanical characterization techniques used to assess the fiber/matrix interfacial properties. In the final outlook, we highlight the key findings and discuss potential directions for characterization of the fiber/matrix interface.

Coil Formation and Biomimetic Performance Characterization of Twisted Coiled Polymer Artificial Muscles

A biological muscle's force is nonlinearly constrained by its current state (force, length, and speed) and state history. To investigate if artificial muscles can mimic (i.e. biomimetic) the complete mechanical state spectrum of biological muscles, this study uses a novel method to characterize twisted coiled polymer actuators (TCPAs) mechanically. Thus, comprehensive and reproducible test procedures are established to verify artificial muscle biomimetics regarding stress, strain, and strain rate combinations intrinsic to biological muscle. A rheometer performs novel high‐precision mechanical characterization methods to comprehensively verify biomimetic performance. Sample twist level, torque, length, force, and temperature are controlled and measured during twist‐induced coiling, heatsetting/annealing, and mechanical testing. TCPAs are formed from linear low‐density polyethylene monofilament. Linear low‐density polyethylene (LLDPE) TCPAs generate larger stresses than biological muscle through the entire spectrum of strains—contracting more than 40%, exerting more than 0.3 MPa at rest length, and withstanding tension of 8 MPa without damage. Thus, the LLDPE TCPAs attain biological muscle performance statically, but additional tests are required to assess this dynamically. The mechanical performance of LLDPE TCPAs enables biomimetic actuation with an intelligent control and measurement system. Their high‐throughput textile manufacturability positions them for advanced biomechatronic applications—including prosthetics and exoskeletons.

Thermally-assisted magnetization of magnetic composites for enhanced micro actuator performance: a low-cost approach using permanent magnets

A micro actuator based on magnetic composite materials can control its deformation and movement through varying magnetic fields, showcasing significant applications in fields such as soft robotics and biomedicine. However, existing magnetic composite materials still require complex magnetization processes involving sophisticated equipment and demanding external magnetic fields. This paper proposed a low-cost, thermally-assisted magnetization process based on permanent magnets. It was observed that the maximum magnetic induction intensity on the surface of magnetic composites is linearly correlated with the heating temperature. Additionally, magnetically treated materials at elevated temperatures can achieve traditional high-field magnetization effects at lower field strengths. Specifically, we synthesized a magnetic composite with 50%wt NdFeB@PDMS and investigated the conditions of the thermally-assisted magnetization process based on permanent magnets, along with mechanical and magnetic performance characterization methods. Experimental results indicate that below 200 °C, the tensile strength and elastic modulus of the base material increase with rising temperatures, demonstrating a trend of high-temperature hardening. However, when the temperature exceeds 200 °C, the elevated temperature leads to the decomposition of the base material, resulting in a rapid decrease in the tensile strength and elastic modulus of the magnetic composite. Furthermore, high temperatures can disrupt the magnetic domains of the magnetic material, reducing its coercive force and making it more susceptible to external magnetic fields and heat, thereby compromising the stability of the magnetic material. These findings provide new insights into the development of more stable and controllable magnetic composite materials.

Compression creep behaviors of GH4169 cylinder entangled wire material at elevated temperatures

As a nickel-based alloy, GH4169 has the properties of excellent corrosion resistance, high temperature oxidation resistance and high creep resistance. In this paper, the compression creep behaviors of cylinder entangled wire materials (CEWMs) made from metal wires (GH4169 nickel-based alloy, 304 stainless steel) were investigated at elevated temperatures (from 400 °C to 500 °C). The performance degradation of the two materials was evaluated by the variation amplitude of four mechanical properties parameters and material characterization methods. The results indicated that both of 304 CEWMs and GH4169 CEWMs suffered a significant performance degradation at elevated temperatures, and both of the two CEWMs showed a much serious performance degradation above 450 °C (tempering temperature). Compared to the 304 CEWMs at the tested temperatures, the GH4169 CEWMs obtained better creep resistance. It is therefore concluded that the GH4169 CEWM is an excellent material that can replace the commonly used 304 CEWM at elevated temperature work conditions.

Structural analysis of small-scale 3D printed composite tidal turbine blades

The existing research literature lacks comprehensive investigations into assessing the structural performance of marine renewable energy conversion devices, particularly 3D printed turbine blades, which often rely solely on computational modelling without experimental validation methods and/or established mechanical characterization techniques. This leads to significant uncertainty regarding the performance of 3D printed turbine blades manufactured by additive manufacturing technology. This study aims to fill this gap by proposing a procedure for evaluating the structural integrity of commercial small-scale tidal turbine blade (5 KW) manufactured using fused filament fabrication 3D printing with a linear infill pattern. This is achieved by developing a combined experimental, hydrodynamic, and finite element approach with the view to inspect the micro-mechanical properties of representative volume elements of 3D printed microstructures using homogenization technique. The results of mechanical testing and hydrodynamic modelling are used to create a finite element model of the 3D printed blade, allowing for stress and failure analysis. Findings indicate that while integrating 3D printed materials into blade design via 3D printing technology is feasible, the choice of materials is limited to high stiffness composite filaments. Finally, experimental validation of numerical results, particularly full field strain distribution maps obtained by digital image correlation technique for flexural testing and laboratory-scale 3D printed blade, confirms the accuracy of the finite element results. Finite element-based homogenization techniques provide valuable insights into potential failure modes in 3D printed tidal turbine blades. However, the expedited calculation of orthotropic properties through finite element analysis proves to be a faster mechanical characterization method compared to experimental approaches. The proposed methodology in this study facilitates quicker iterative design of 3D printed blades, thereby reducing the need for repeated experiments and ultimately lowering manufacturing costs.

Simulation of a synchronized methodology for MR-based electromechanical property imaging during transcranial electrical stimulation

Introduction: Recent investigations into the biomechanics of the brain have unveiled alteration in tissue stiffness triggered by external stimuli. For instance, visual stimulation effects can be measured in elasticity images of the cortex generated by functional magnetic resonance elastography (MRE). Such a mechanical characterization method combined with non-invasive brain stimulation (NIBS), a technique that seeks to selectively modulate particular parts of the brain using weak electrical currents, has the potential to influence research on various neurological disorders. In this in silico study, we aimed to elucidate individual and interdependent aspects related to a synchronized biomechanical imaging and non-invasive brain stimulation methodology. Magnetic resonance electrical impedance tomography (MREIT) was incorporated to the pipeline, providing a promising way of evaluating NIBS-induced electrical current patterns in the brain while leveraging MRE and transcranial alternating current stimulation (tACS) experimental settings.Methods: A mouse head model was assembled using open-access atlases to include five anatomical structures: skin/subcutaneous tissue, skull, cerebrospinal fluid (CSF), brain white and grey matters. MRE, tACS, and MREIT experiments were simulated using Comsol Multiphysics with Matlab Livelink. Synthetic MRE and MREIT data were processed using the subzone non-linear inversion and harmonic Bz algorithm, respectively, to reconstruct images of the distributed complex shear modulus and electrical conductivity.Results and Discussion: Lorentz body forces arising from simultaneous MRE and tACS elicited elastic waves of negligible amplitude compared with the extrinsic actuation levels reported in the literature, which allowed accurate reconstructions of the complex shear modulus. Qualitative electrical conductivity maps retrieved by MREIT accurately delineated anatomical regions of the brain model and could be used to recover reasonably accurate distributions of tACS-induced currents. This multi-physics approach has potential for translation to human brain imaging, and may provide more possibilities for the characterization of brain function together than in isolation.

Analysis of the manufacturing of concrete paving blocks with by-products from thermoelectric power plant

The key factor in constructing urban roads applying interlocking concrete block pavement (ICBP) is to employ an appropriate design method for better effectiveness. Concrete paving blocks (CPB) can also be manufactured using industrial by-products. Then, this paper aims to analyze CPB with coal bottom ash (CBA) from a Thermoelectric Power Plant through mechanical characterization and design methods for ICBP. To this end, tests, such as void index, water absorption, compressive strength, and elasticity modulus, were done on CPB for each mixture. Furthermore, empirical and mechanistic-empirical design methods for ICBP were applied. Then, four dry concrete mixtures (two with CBA and two without CBA) were designed with two water/cement ratios (0.63 and 0.73) to produce rectangular CPB measuring 20 cm × 10 cm × 8 cm (length × width × thickness) by a vibro-press machine. Furthermore, ICBP sections were designed, applying six simulations from empirical and mechanistic-empirical design methods. The results showed that the mixtures A73 and B73 with more water, i.e., water/cement ratio of 0.73, presented higher characteristic compressive strength at 28 days (25.34 MPa and 15.88 MPa, respectively) than the other mixes A63 and B63 with less water, i.e., water/cement ratio of 0.63 (these two mixes showed 15.85 MPa). Furthermore, the CPB application for bike paths or parking areas was allowed according to the Australian specification of 15 MPa for compressive strength test. Also, all ICBP sections from the mechanistic-empirical design required approximately 24.9% fewer materials for the sub-base layer than the empirical process. Finally, the CPB application is possible for areas with light traffic, and the ICBP technology was more feasible with the mechanistic-empirical design method.

Tough Hydrogels for Load-Bearing Applications.

Tough hydrogels have emerged as a promising class of materials to target load-bearing applications, where the material has to resist multiple cycles of extreme mechanical impact. A variety of chemical interactions and network architectures are used to enhance the mechanical properties and fracture mechanics of hydrogels making them stiffer and tougher. In recent years, the mechanical properties of tough, high-performance hydrogels have been benchmarked, however, this is often incomplete as important variables like water content are largely ignored. In this review, the aim is to clarify the reported mechanical properties of state-of-the-art tough hydrogels by providing a comprehensive library of fracture and mechanical property data. First, common methods for mechanical characterization of such high-performance hydrogels are introduced. Then, various modes of energy dissipation to obtain tough hydrogels are discussed and used to categorize the individual datasets helping to asses the material's (fracture) mechanical properties. Finally, current applications are considered, tough high-performance hydrogels are compared with existing materials, and promising future opportunities are discussed.

Ultrasonic elastography for the prevention of breast implant rupture: Detection of an increase with stiffness over implantation time

Breast implants are widely used after breast cancer resection and must be changed regularly to avoid a rupture. To date, there are no quantitative criteria to help this decision. The mechanical evolution of the gels and membranes of the implants is still underinvestigated, although it can lead to early rupture. In this study, 35 breast explants having been implanted in patients for up to 17 years were characterized by ex vivo measurements of their mechanical properties. Using Acoustic Radiation Force Impulse (ARFI) ultrasound elastography, an imaging method for non-destructive mechanical characterization, an increase in the stiffness of the explants has been observed. This increase was correlated with the implantation duration, primarily after 8 years of implantation. With an increase of the shear modulus of up to a factor of nearly 3, the loss of flexibility of the implants is likely to lead to a significant increase of their risk of rupture. A complementary analysis of the gel from the explants by mass spectrometry imaging (MSI) and liquid chromatography coupled to high resolution mass spectrometry (LC-HRMS) confirms the presence of metabolites of cholesterol originating from the breast tissues, which most likely crossed the membrane of the implants and most likely degrades the gel. By observing the consequences of the physical–chemical mechanisms at work within patients, this study shows that ultrasound elastography could be used in vivoas a quantitative indicator of the risk of breast implant rupture and help diagnose their replacement.

Regional biomechanical characterization of the spinal cord tissue: dynamic mechanical response.

Characterizing the dynamic mechanical properties of spinal cord tissue is deemed important for developing a comprehensive knowledge of the mechanisms underlying spinal cord injury. However, complex viscoelastic properties are vastly underexplored due to the spinal cord shows heterogeneous properties. To investigate regional differences in the biomechanical properties of spinal cord, we provide a mechanical characterization method (i.e., dynamic mechanical analysis) that facilitates robust measurement of spinal cord ex vivo, at small deformations, in the dynamic regimes. Load-unload cycles were applied to the tissue surface at sinusoidal frequencies of 0.05, 0.10, 0.50 and 1.00Hz ex vivo within 2h post mortem. We report the main response features (e.g., nonlinearities, rate dependencies, hysteresis and conditioning) of spinal cord tissue dependent on anatomical origin, and quantify the viscoelastic properties through the measurement of peak force, moduli, and hysteresis and energy loss. For all three anatomical areas (cervical, thoracic, and lumbar spinal cord tissues), the compound, storage, and loss moduli responded similarly to increasing strain rates. Notably, the complex modulus values of ex vivo spinal cord tissue rose nonlinearly with rising test frequency. Additionally, at every strain rate, it was shown that the tissue in the thoracic spinal cord was significantly more rigid than the tissue in the cervical or lumbar spinal cord, with compound modulus values roughly 1.5-times that of the lumbar region. At strain rates between 0.05 and 0.50Hz, tan δ values for thoracic (that is, 0.26, 0.25, 0.06, respectively) and lumbar (that is, 0.27, 0.25, 0.07, respectively) spinal cord regions were similar, respectively, which were higher than cervical (that is, 0.21, 0.21, 0.04, respectively) region. The conditioning effects tend to be greater at relative higher deformation rates. Interestingly, no marked difference of conditioning ratios is observed among all three anatomical regions, regardless of loading rate. These findings lay a foundation for further comparison between healthy and diseased spinal cord to the future development of spinal cord scaffold and helps to advance our knowledge of neuroscience.

Tension-Induced Localized Wrinkling in a Patched Thin Film Supported by an Elastomer.

The wrinkling behavior of thin films has received great attention for their applications in developing various wrinkle-based novel technologies. Herein, a new wrinkling system: tension-induced wrinkling in an elastomer-supported patched thin film (TW-P&SF) is investigated by using PDMS-supported patched polyimide thin films with different thicknesses and varied length/width ratios. Different from the well-studied compression-induced wrinkling in an elastomer-supported thin film (CW-SF) and tension-induced wrinkling in an edge-clamped free-standing thin film (TW-FF), in the system of TW-P&SF, the wrinkles are localized near the edge of the film with a finite length that follows a center-symmetric distribution. It was found that the wrinkle length lmax and the wrinkle period λ scale with the film thickness h as λ ∼ h0.86 and lmax ∼ h-0.79. With the assistance of the two-dimensional shear lag model and scaling analysis, the underlying mechanism for wrinkle localization is clarified. Furthermore, the promise of the TW-P&SF-enabled wrinkle-based method as a new method for thin film mechanical characterization is demonstrated.

A 3D printed tensile testing system for micro-scale specimens

Mechanical property characterization of micro-scale material systems, such as free-standing films or small diameter wires (<20 µm), often requires expensive, specialized test systems. Conventional tensile test systems are usually designed for millimeter scale specimens with the force sensing capability of >1N while microdevice-based testers are intended for micro-/nano-scale specimens operating within a much smaller force range of <10 mN. This disparity leaves a technology gap in reliable and cost-effective characterization methods for specimens at the intermediate scale. In this research, we introduce the cost-effective and all-in-one tensile testing system with a built-in force sensor, self-aligning mechanisms, and loading frames. Owing to the advantages of 3D printing technologies, the ranges of force measurement (0.001–1 N) and displacement (up to tens of millimeters) of our 3D printed tensile tester can be readily tailored to suit specific material dimension and types. We have conducted a finite element simulation to identify the potential sources of the measurement error during tensile testing and addressed the dominant errors by simply modifying the dimension/design of the loading frames. As a proof-of-concept demonstration, we have characterized fine copper (Cu) wires with 10–25 µm diameters by the 3D printed tensile tester and confirmed that the measured mechanical properties match with the known values of bulk Cu. Our work shows that the proposed 3D printed tensile testing system offers a cost-efficient and easily accessible testing method for accurate mechanical characterization of specimens with cross-sectional dimensions of the order of tens of micrometers.

A Fractional Creep Constitutive Model Considering the Viscoelastic-Viscoplastic Coexistence Mechanism.

In order to improve the accuracy and universality of the nonlinear viscoelastic-plastic mechanical behavior characterization method of asphalt mixture, a new criterion for the division of the creep process of materials was established based on the strain yield characteristics, and the coexistence mechanism of Viscoelastic-Viscoplastic strain was proposed in the subsequent yield phase; then, a viscoelastic element was constructed in the form of a parallel connection of two fractional viscoelastic elements based on fractional calculus theory, and its mathematical equations were derived; with novel viscoelastic elements, a constitutive model characterizing the whole creep process of asphalt mixtures was developed and its analytical expression was derived. The laboratory short-term creep test of Cement and Asphalt Mortar (CA mortar) and the simulation test data of asphalt mixtures from the references were used to verify the constitutive model. The results show that the creep constitutive model of asphalt mixture established in this paper has excellent fitting accuracy for different phases of the creep process of asphalt mixture under different stress levels, where the minimum fitting correlation values R2 for CA mortar, asphalt mixture (applied to pavement engineering), and asphalt sand are 0.9976, 0.981, and 0.979, respectively. Therefore, this model can be used to provide a theoretical reference for the study of the characterization of the mechanical behavior of asphalt materials.

Functional properties of nano-SiO2/pinewood-derived cellulose acetate composite film for packaging application

Petroleum-based plastics are widely used because of their practicable properties and low cost. However, people are equally concerned about the environmental damage generated by non-biodegradable petrochemical plastics. In this study, pinewood was employed as the raw material to prepare cellulose acetate and further synthesize the degradable composite films, which showed potential feasibilities to substitute the traditional petroleum-based plastics. In order to improve the barrier performance, hydrophobic performance, and mechanical properties of the film materials, nano-SiO2 was introduced as functional filler for experimental exploration. The tensile strength, light transmittance, water vapor transmittance, microstructure, and crystalline structure of the nano-SiO2/pinewood-derived cellulose acetate composite films were determined by mechanical analysis, optical analysis, SEM, XRD, FT-IR, and barrier characterization methods, respectively. The results exhibited that the prepared films with the inclusion of nano-SiO2 did not conduct reduction in transparency due to its good dispersion in the composite film. The barrier property, hydrophobic performance, and mechanical properties of cellulose acetate composite film were effectively improved due to the interaction between nano-SiO2 and cellulose acetate molecular chains by the hydrogen bonds formed between hydroxyl groups. It was confirmed that the nano-SiO2/pinewood-derived cellulose acetate composite films exhibit great application potential as an environmentally friendly and efficient material for packaging.

Mechanical characterization of osteoporosis based on x-ray induced acoustic computed tomography

X-ray induced acoustic computed tomography (XACT) utilized the ultrasound generated by the thermoelastic effect to reconstruct the x-ray absorption distribution of tissues. In this Letter, we propose a method for mechanical characterization of osteoporosis based on an XACT technique. The theoretical and simulation studies were performed on the influence of elasticity effect on x-ray induced acoustic (XA) generation. The images of normal and osteoporotic bones reconstructed by the simulated XACT were found to be in good agreement with micro-CT. Furthermore, through XA signal analysis, the rise time of tissue displacement can be obtained to characterize the elasticity of bone tissues. Experimental results demonstrated that this method can provide structural and mechanical information of bone tissues, which has future potentials for assessment of bone in osteoporosis.

Experimental Investigation of Aerospace Grade Composites Porosity Laminates Under Hygro-Thermal Environment Condition

The effect of porosity has been studied by developing different levels of porosity laminates through a new autoclave based manufacturing technique known as Diverse Cure System (DCS). Further assessment of porosity levels by mechanical characterization (Inter-laminar Shear Strength), microscopic studies and acid digestion method have been achieved in Carbon Fiber Epoxy laminates. Correlations are obtained on the different levels for porosity laminates of two different thicknesses. ILSS test results are compared with the literature results. Assessment of porosity effect on ILSS is performed at room temperature and environmentally conditioned specimens. Strength degradation of 20 to 30% has been noticed on porosity laminates. Hygro-thermal specimens are tested at room temperature, elevated temperature and hot wet condition. A large reduction in the range of 45 to 53% in ILSS has been noticed on the moisture conditioned specimens tested at elevated temperature of 150°C.

Beyond Chainmail: Computational Modeling of Discrete Interlocking Materials

We present a method for computational modeling, mechanical characterization, and macro-scale simulation of discrete interlocking materials (DIM)---3D-printed chainmail fabrics made of quasi-rigid interlocking elements. Unlike conventional elastic materials for which deformation and restoring force are directly coupled, the mechanics of DIM are governed by contacts between individual elements that give rise to anisotropic deformation constraints. To model the mechanical behavior of these materials, we propose a computational approach that builds on three key components. ( a ): we explore the space of feasible deformations using native-scale simulations at the per-element level. ( b ): based on this simulation data, we introduce the concept of strain-space boundaries to represent deformation limits for in- and out-of-plane deformations, and ( c ): we use the strain-space boundaries to drive an efficient macro-scale simulation model based on homogenized deformation constraints. We evaluate our method on a set of representative discrete interlocking materials and validate our findings against measurements on physical prototypes.

Machine learning based dual flat-spherical indentation approach for rough metallic surfaces

Instrumented indentation test (IIT) is regarded as one of the non-destructive test methods for mechanical characterization and safety assessment of engineering components. However, indentation test is very sensitive to surface topography i.e surface roughness, requiring specimens with ideally flat and smooth surface for producing reliable and reproducible test results. Recently, a dual flat-spherical indentation (DFSI) technique was proposed to extract material properties directly from rough metallic surface via indentation tests. Integration of DFSI technique with machine learning (ML) approach can facilitate reliable and fast characterization of rough metallic surfaces. Here, ML models including artificial neural network (ANN) and physics-informed artificial neural network (PI-ANN) are established, and then trained by using a database of indentation parameters generated via DFSI simulations. Spherical indentation techniques available in the literature are used to calculate the physics-informed loss in the PI-ANN model. The performances of trained ANN and PI-ANN models are compared, and an optimal ML model with hyperparameters is suggested based on validation study; PI-ANN model with sigmoid activation function shows a better performance than the ANN model and baseline model. The model performances are evaluated by performing DFSI experiments with SM45C and SS304. The applicability of ML based-DFSI method is demonstrated for extracting the mechanical properties from the rough surface of general metals.

Pressure-induced nonlinear resonance frequency changes for extracting Young’s modulus of nanodrums

The resonance frequency of ultra-thin layered nanomaterials changes nonlinearly with the tension induced by the pressure from the surrounding gas. Although the dynamics of pressurized nanomaterial membranes have been extensively explored, recent experimental observations show significant deviations from analytical predictions. Here, we present a multi-mode continuum model that captures the nonlinear pressure-frequency response of pre-tensioned membranes undergoing large deflections. We validate the model using experiments conducted on polysilicon nanodrums excited opto-thermally and subjected to pressure changes in the surrounding medium. We demonstrate that considering the effect of pressure on the nanodrum tension is not sufficient for determining the resonance frequencies. In fact, it is essential to also account for the change in the membrane’s shape in the pressurized configuration, the mid-plane stretching, and the contributions of higher modes to the mode shapes. Finally, we show how the presented high-frequency mechanical characterization method can serve as a fast and contactless method for determining Young’s modulus of ultra-thin membranes.

Degradation of PET – Quantitative estimation of changes in molar mass using mechanical and thermal characterization methods

Polyethylene terephthalate (PET) films are used when mechanical strength, thermal and chemical stability, and barrier properties to atmospheric gases are required in combination with good processability. Hydrolysis leading to embrittlement of the material is a major concern as PET is used in a variety of applications with expected lifetimes of up to decades (e.g., for use in buildings, textiles, or photovoltaic backsheets). Therefore, a comprehensive understanding of the degradation processes and the effects on the molecular mass distribution is of great importance.Usually, the direct determination of molar mass and molar mass distribution involves high effort and sophisticated equipment. Therefore, the main objective of this work is to quantify molar mass changes due to accelerated aging using thermal and mechanical methods. Two stabilized PET films were subjected to seven different accelerated aging conditions (heat; combined heat-humidity). The samples were then characterized by size exclusion chromatography (SEC), tensile tests and differential scanning calorimetry (DSC).A linear correlation was found between crystallization temperature and average molar mass. The values of fracture stress from tensile tests indicate a ductile-brittle transition at a molar mass of 15 000 g mol−1. The study concludes that the crystallization temperature obtained from DSC measurements can be used to estimate changes in the average molar mass of PET after hydrolysis. Crystallization temperatures between 208 °C and 211 °C correspond to a critical reduction in molar mass and severe embrittlement.